rockbox/apps/plugins/jpeg.c

/***************************************************************************
*             __________               __   ___.
*   Open      \______   \ ____   ____ |  | _\_ |__   _______  ___
*   Source     |       _//  _ \_/ ___\|  |/ /| __ \ /  _ \  \/  /
*   Jukebox    |    |   (  <_> )  \___|    < | \_\ (  <_> > <  <
*   Firmware   |____|_  /\____/ \___  >__|_ \|___  /\____/__/\_ \
*                     \/            \/     \/    \/            \/
* $Id$
*
* JPEG image viewer
* (This is a real mess if it has to be coded in one single C file)
*
* Copyright (C) 2004 J<EFBFBD>rg Hohensohn aka [IDC]Dragon
* Grayscale framework (c) 2004 Jens Arnold
* Heavily borrowed from the IJG implementation (c) Thomas G. Lane
* Small & fast downscaling IDCT (c) 2002 by Guido Vollbeding  JPEGclub.org
*
* All files in this archive are subject to the GNU General Public License.
* See the file COPYING in the source tree root for full license agreement.
*
* This software is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY
* KIND, either express or implied.
*
****************************************************************************/

#ifndef SIMULATOR /* not for simulator by now */
#include "plugin.h"

#ifdef HAVE_LCD_BITMAP /* and also not for the Player */
#include "gray.h"

/******************************* Globals ***********************************/

static struct plugin_api* rb;

/* for portability of below JPEG code */
#define MEMSET(p,v,c) rb->memset(p,v,c)
#define INLINE static inline
#define ENDIAN_SWAP16(n) n /* only for poor little endian machines */



/**************** begin JPEG code ********************/

/* LUT for IDCT, this could also be used for gamma correction */
const unsigned char range_limit[1024] =
{
    128,129,130,131,132,133,134,135,136,137,138,139,140,141,142,143,
    144,145,146,147,148,149,150,151,152,153,154,155,156,157,158,159,
    160,161,162,163,164,165,166,167,168,169,170,171,172,173,174,175,
    176,177,178,179,180,181,182,183,184,185,186,187,188,189,190,191,
    192,193,194,195,196,197,198,199,200,201,202,203,204,205,206,207,
    208,209,210,211,212,213,214,215,216,217,218,219,220,221,222,223,
    224,225,226,227,228,229,230,231,232,233,234,235,236,237,238,239,
    240,241,242,243,244,245,246,247,248,249,250,251,252,253,254,255,

    255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,
    255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,
    255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,
    255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,
    255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,
    255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,
    255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,
    255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,
    255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,
    255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,
    255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,
    255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,
    255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,
    255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,
    255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,
    255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,
    255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,
    255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,
    255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,
    255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,
    255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,
    255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,
    255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,
    255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,

    0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
    0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
    0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
    0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
    0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
    0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
    0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
    0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
    0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
    0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
    0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
    0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
    0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
    0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
    0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
    0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
    0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
    0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
    0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
    0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
    0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
    0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
    0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
    0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,

    0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,
    16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,
    32,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,
    48,49,50,51,52,53,54,55,56,57,58,59,60,61,62,63,
    64,65,66,67,68,69,70,71,72,73,74,75,76,77,78,79,
    80,81,82,83,84,85,86,87,88,89,90,91,92,93,94,95,
    96,97,98,99,100,101,102,103,104,105,106,107,108,109,110,111,
    112,113,114,115,116,117,118,119,120,121,122,123,124,125,126,127
};


/* IDCT implementation */


#define CONST_BITS 13
#define PASS1_BITS 2


/* Some C compilers fail to reduce "FIX(constant)" at compile time, thus
* causing a lot of useless floating-point operations at run time.
* To get around this we use the following pre-calculated constants.
* If you change CONST_BITS you may want to add appropriate values.
* (With a reasonable C compiler, you can just rely on the FIX() macro...)
*/
#define FIX_0_298631336  2446 /* FIX(0.298631336) */
#define FIX_0_390180644  3196 /* FIX(0.390180644) */
#define FIX_0_541196100  4433 /* FIX(0.541196100) */
#define FIX_0_765366865  6270 /* FIX(0.765366865) */
#define FIX_0_899976223  7373 /* FIX(0.899976223) */
#define FIX_1_175875602  9633 /* FIX(1.175875602) */
#define FIX_1_501321110 12299 /* FIX(1.501321110) */
#define FIX_1_847759065 15137 /* FIX(1.847759065) */
#define FIX_1_961570560 16069 /* FIX(1.961570560) */
#define FIX_2_053119869 16819 /* FIX(2.053119869) */
#define FIX_2_562915447 20995 /* FIX(2.562915447) */
#define FIX_3_072711026 25172 /* FIX(3.072711026) */



/* Multiply an long variable by an long constant to yield an long result.
* For 8-bit samples with the recommended scaling, all the variable
* and constant values involved are no more than 16 bits wide, so a
* 16x16->32 bit multiply can be used instead of a full 32x32 multiply.
* For 12-bit samples, a full 32-bit multiplication will be needed.
*/
#define MULTIPLY16(var,const)  (((short) (var)) * ((short) (const)))


/* Dequantize a coefficient by multiplying it by the multiplier-table
* entry; produce an int result.  In this module, both inputs and result
* are 16 bits or less, so either int or short multiply will work.
*/
/* #define DEQUANTIZE(coef,quantval)  (((int) (coef)) * (quantval)) */
#define DEQUANTIZE MULTIPLY16

/* Descale and correctly round an int value that's scaled by N bits.
* We assume RIGHT_SHIFT rounds towards minus infinity, so adding
* the fudge factor is correct for either sign of X.
*/
#define DESCALE(x,n) (((x) + (1l << ((n)-1))) >> (n))

#define RANGE_MASK (255 * 4 + 3) /* 2 bits wider than legal samples */



/*
* Perform dequantization and inverse DCT on one block of coefficients,
* producing a reduced-size 1x1 output block.
*/
void idct1x1(unsigned char* p_byte, int* inptr, int* quantptr, int skip_line)
{
    (void)skip_line; /* unused */
    *p_byte = range_limit[(inptr[0] * quantptr[0] >> 3) & RANGE_MASK];
}



/*
* Perform dequantization and inverse DCT on one block of coefficients,
* producing a reduced-size 2x2 output block.
*/
void idct2x2(unsigned char* p_byte, int* inptr, int* quantptr, int skip_line)
{
    int tmp0, tmp1, tmp2, tmp3, tmp4, tmp5;
    unsigned char* outptr;

    /* Pass 1: process columns from input, store into work array. */

    /* Column 0 */
    tmp4 = DEQUANTIZE(inptr[8*0], quantptr[8*0]);
    tmp5 = DEQUANTIZE(inptr[8*1], quantptr[8*1]);

    tmp0 = tmp4 + tmp5;
    tmp2 = tmp4 - tmp5;

    /* Column 1 */
    tmp4 = DEQUANTIZE(inptr[8*0+1], quantptr[8*0+1]);
    tmp5 = DEQUANTIZE(inptr[8*1+1], quantptr[8*1+1]);

    tmp1 = tmp4 + tmp5;
    tmp3 = tmp4 - tmp5;

    /* Pass 2: process 2 rows, store into output array. */

    /* Row 0 */
    outptr = p_byte;

    outptr[0] = range_limit[(int) DESCALE(tmp0 + tmp1, 3)
        & RANGE_MASK];
    outptr[1] = range_limit[(int) DESCALE(tmp0 - tmp1, 3)
        & RANGE_MASK];

    /* Row 1 */
    outptr = p_byte + skip_line;

    outptr[0] = range_limit[(int) DESCALE(tmp2 + tmp3, 3)
        & RANGE_MASK];
    outptr[1] = range_limit[(int) DESCALE(tmp2 - tmp3, 3)
        & RANGE_MASK];
}



/*
* Perform dequantization and inverse DCT on one block of coefficients,
* producing a reduced-size 4x4 output block.
*/
void idct4x4(unsigned char* p_byte, int* inptr, int* quantptr, int skip_line)
{
    int tmp0, tmp2, tmp10, tmp12;
    int z1, z2, z3;
    int * wsptr;
    unsigned char* outptr;
    int ctr;
    int workspace[4*4]; /* buffers data between passes */

    /* Pass 1: process columns from input, store into work array. */

    wsptr = workspace;
    for (ctr = 0; ctr < 4; ctr++, inptr++, quantptr++, wsptr++)
    {
        /* Even part */

        tmp0 = DEQUANTIZE(inptr[8*0], quantptr[8*0]);
        tmp2 = DEQUANTIZE(inptr[8*2], quantptr[8*2]);

        tmp10 = (tmp0 + tmp2) << PASS1_BITS;
        tmp12 = (tmp0 - tmp2) << PASS1_BITS;

        /* Odd part */
        /* Same rotation as in the even part of the 8x8 LL&M IDCT */

        z2 = DEQUANTIZE(inptr[8*1], quantptr[8*1]);
        z3 = DEQUANTIZE(inptr[8*3], quantptr[8*3]);

        z1 = MULTIPLY16(z2 + z3, FIX_0_541196100);
        tmp0 = DESCALE(z1 + MULTIPLY16(z3, - FIX_1_847759065), CONST_BITS-PASS1_BITS);
        tmp2 = DESCALE(z1 + MULTIPLY16(z2, FIX_0_765366865), CONST_BITS-PASS1_BITS);

        /* Final output stage */

        wsptr[4*0] = (int) (tmp10 + tmp2);
        wsptr[4*3] = (int) (tmp10 - tmp2);
        wsptr[4*1] = (int) (tmp12 + tmp0);
        wsptr[4*2] = (int) (tmp12 - tmp0);
    }

    /* Pass 2: process 4 rows from work array, store into output array. */

    wsptr = workspace;
    for (ctr = 0; ctr < 4; ctr++)
    {
        outptr = p_byte + (ctr*skip_line);
        /* Even part */

        tmp0 = (int) wsptr[0];
        tmp2 = (int) wsptr[2];

        tmp10 = (tmp0 + tmp2) << CONST_BITS;
        tmp12 = (tmp0 - tmp2) << CONST_BITS;

        /* Odd part */
        /* Same rotation as in the even part of the 8x8 LL&M IDCT */

        z2 = (int) wsptr[1];
        z3 = (int) wsptr[3];

        z1 = MULTIPLY16(z2 + z3, FIX_0_541196100);
        tmp0 = z1 + MULTIPLY16(z3, - FIX_1_847759065);
        tmp2 = z1 + MULTIPLY16(z2, FIX_0_765366865);

        /* Final output stage */

        outptr[0] = range_limit[(int) DESCALE(tmp10 + tmp2,
            CONST_BITS+PASS1_BITS+3)
            & RANGE_MASK];
        outptr[3] = range_limit[(int) DESCALE(tmp10 - tmp2,
            CONST_BITS+PASS1_BITS+3)
            & RANGE_MASK];
        outptr[1] = range_limit[(int) DESCALE(tmp12 + tmp0,
            CONST_BITS+PASS1_BITS+3)
            & RANGE_MASK];
        outptr[2] = range_limit[(int) DESCALE(tmp12 - tmp0,
            CONST_BITS+PASS1_BITS+3)
            & RANGE_MASK];

        wsptr += 4;     /* advance pointer to next row */
    }
}



/*
* Perform dequantization and inverse DCT on one block of coefficients.
*/
void idct8x8(unsigned char* p_byte, int* inptr, int* quantptr, int skip_line)
{
    long tmp0, tmp1, tmp2, tmp3;
    long tmp10, tmp11, tmp12, tmp13;
    long z1, z2, z3, z4, z5;
    int * wsptr;
    unsigned char* outptr;
    int ctr;
    static int workspace[64];  /* buffers data between passes */

    /* Pass 1: process columns from input, store into work array. */
    /* Note results are scaled up by sqrt(8) compared to a true IDCT; */
    /* furthermore, we scale the results by 2**PASS1_BITS. */

    wsptr = workspace;
    for (ctr = 8; ctr > 0; ctr--)
    {
    /* Due to quantization, we will usually find that many of the input
    * coefficients are zero, especially the AC terms.  We can exploit this
    * by short-circuiting the IDCT calculation for any column in which all
    * the AC terms are zero.  In that case each output is equal to the
    * DC coefficient (with scale factor as needed).
    * With typical images and quantization tables, half or more of the
    * column DCT calculations can be simplified this way.
    */

        if ((inptr[8*1] | inptr[8*2] | inptr[8*3]
           | inptr[8*4] | inptr[8*5] | inptr[8*6] | inptr[8*7]) == 0)
        {
            /* AC terms all zero */
            int dcval = DEQUANTIZE(inptr[8*0], quantptr[8*0]) << PASS1_BITS;

            wsptr[8*0] = wsptr[8*1] = wsptr[8*2] = wsptr[8*3] = wsptr[8*4]
                       = wsptr[8*5] = wsptr[8*6] = wsptr[8*7] = dcval;
            inptr++;      /* advance pointers to next column */
            quantptr++;
            wsptr++;
            continue;
        }

        /* Even part: reverse the even part of the forward DCT. */
        /* The rotator is sqrt(2)*c(-6). */

        z2 = DEQUANTIZE(inptr[8*2], quantptr[8*2]);
        z3 = DEQUANTIZE(inptr[8*6], quantptr[8*6]);

        z1 = MULTIPLY16(z2 + z3, FIX_0_541196100);
        tmp2 = z1 + MULTIPLY16(z3, - FIX_1_847759065);
        tmp3 = z1 + MULTIPLY16(z2, FIX_0_765366865);

        z2 = DEQUANTIZE(inptr[8*0], quantptr[8*0]);
        z3 = DEQUANTIZE(inptr[8*4], quantptr[8*4]);

        tmp0 = (z2 + z3) << CONST_BITS;
        tmp1 = (z2 - z3) << CONST_BITS;

        tmp10 = tmp0 + tmp3;
        tmp13 = tmp0 - tmp3;
        tmp11 = tmp1 + tmp2;
        tmp12 = tmp1 - tmp2;

        /* Odd part per figure 8; the matrix is unitary and hence its
           transpose is its inverse.  i0..i3 are y7,y5,y3,y1 respectively. */

        tmp0 = DEQUANTIZE(inptr[8*7], quantptr[8*7]);
        tmp1 = DEQUANTIZE(inptr[8*5], quantptr[8*5]);
        tmp2 = DEQUANTIZE(inptr[8*3], quantptr[8*3]);
        tmp3 = DEQUANTIZE(inptr[8*1], quantptr[8*1]);

        z1 = tmp0 + tmp3;
        z2 = tmp1 + tmp2;
        z3 = tmp0 + tmp2;
        z4 = tmp1 + tmp3;
        z5 = MULTIPLY16(z3 + z4, FIX_1_175875602); /* sqrt(2) * c3 */

        tmp0 = MULTIPLY16(tmp0, FIX_0_298631336); /* sqrt(2) * (-c1+c3+c5-c7) */
        tmp1 = MULTIPLY16(tmp1, FIX_2_053119869); /* sqrt(2) * ( c1+c3-c5+c7) */
        tmp2 = MULTIPLY16(tmp2, FIX_3_072711026); /* sqrt(2) * ( c1+c3+c5-c7) */
        tmp3 = MULTIPLY16(tmp3, FIX_1_501321110); /* sqrt(2) * ( c1+c3-c5-c7) */
        z1 = MULTIPLY16(z1, - FIX_0_899976223); /* sqrt(2) * (c7-c3) */
        z2 = MULTIPLY16(z2, - FIX_2_562915447); /* sqrt(2) * (-c1-c3) */
        z3 = MULTIPLY16(z3, - FIX_1_961570560); /* sqrt(2) * (-c3-c5) */
        z4 = MULTIPLY16(z4, - FIX_0_390180644); /* sqrt(2) * (c5-c3) */

        z3 += z5;
        z4 += z5;

        tmp0 += z1 + z3;
        tmp1 += z2 + z4;
        tmp2 += z2 + z3;
        tmp3 += z1 + z4;

        /* Final output stage: inputs are tmp10..tmp13, tmp0..tmp3 */

        wsptr[8*0] = (int) DESCALE(tmp10 + tmp3, CONST_BITS-PASS1_BITS);
        wsptr[8*7] = (int) DESCALE(tmp10 - tmp3, CONST_BITS-PASS1_BITS);
        wsptr[8*1] = (int) DESCALE(tmp11 + tmp2, CONST_BITS-PASS1_BITS);
        wsptr[8*6] = (int) DESCALE(tmp11 - tmp2, CONST_BITS-PASS1_BITS);
        wsptr[8*2] = (int) DESCALE(tmp12 + tmp1, CONST_BITS-PASS1_BITS);
        wsptr[8*5] = (int) DESCALE(tmp12 - tmp1, CONST_BITS-PASS1_BITS);
        wsptr[8*3] = (int) DESCALE(tmp13 + tmp0, CONST_BITS-PASS1_BITS);
        wsptr[8*4] = (int) DESCALE(tmp13 - tmp0, CONST_BITS-PASS1_BITS);

        inptr++; /* advance pointers to next column */
        quantptr++;
        wsptr++;
    }

    /* Pass 2: process rows from work array, store into output array. */
    /* Note that we must descale the results by a factor of 8 == 2**3, */
    /* and also undo the PASS1_BITS scaling. */

    wsptr = workspace;
    for (ctr = 0; ctr < 8; ctr++)
    {
        outptr = p_byte + (ctr*skip_line);
        /* Rows of zeroes can be exploited in the same way as we did with columns.
        * However, the column calculation has created many nonzero AC terms, so
        * the simplification applies less often (typically 5% to 10% of the time).
        * On machines with very fast multiplication, it's possible that the
        * test takes more time than it's worth.  In that case this section
        * may be commented out.
        */

#ifndef NO_ZERO_ROW_TEST
        if ((wsptr[1] | wsptr[2] | wsptr[3]
           | wsptr[4] | wsptr[5] | wsptr[6] | wsptr[7]) == 0)
        {
            /* AC terms all zero */
            unsigned char dcval = range_limit[(int) DESCALE((long) wsptr[0],
                PASS1_BITS+3) & RANGE_MASK];

            outptr[0] = dcval;
            outptr[1] = dcval;
            outptr[2] = dcval;
            outptr[3] = dcval;
            outptr[4] = dcval;
            outptr[5] = dcval;
            outptr[6] = dcval;
            outptr[7] = dcval;

            wsptr += 8; /* advance pointer to next row */
            continue;
        }
#endif

        /* Even part: reverse the even part of the forward DCT. */
        /* The rotator is sqrt(2)*c(-6). */

        z2 = (long) wsptr[2];
        z3 = (long) wsptr[6];

        z1 = MULTIPLY16(z2 + z3, FIX_0_541196100);
        tmp2 = z1 + MULTIPLY16(z3, - FIX_1_847759065);
        tmp3 = z1 + MULTIPLY16(z2, FIX_0_765366865);

        tmp0 = ((long) wsptr[0] + (long) wsptr[4]) << CONST_BITS;
        tmp1 = ((long) wsptr[0] - (long) wsptr[4]) << CONST_BITS;

        tmp10 = tmp0 + tmp3;
        tmp13 = tmp0 - tmp3;
        tmp11 = tmp1 + tmp2;
        tmp12 = tmp1 - tmp2;

        /* Odd part per figure 8; the matrix is unitary and hence its
        * transpose is its inverse. i0..i3 are y7,y5,y3,y1 respectively. */

        tmp0 = (long) wsptr[7];
        tmp1 = (long) wsptr[5];
        tmp2 = (long) wsptr[3];
        tmp3 = (long) wsptr[1];

        z1 = tmp0 + tmp3;
        z2 = tmp1 + tmp2;
        z3 = tmp0 + tmp2;
        z4 = tmp1 + tmp3;
        z5 = MULTIPLY16(z3 + z4, FIX_1_175875602); /* sqrt(2) * c3 */

        tmp0 = MULTIPLY16(tmp0, FIX_0_298631336); /* sqrt(2) * (-c1+c3+c5-c7) */
        tmp1 = MULTIPLY16(tmp1, FIX_2_053119869); /* sqrt(2) * ( c1+c3-c5+c7) */
        tmp2 = MULTIPLY16(tmp2, FIX_3_072711026); /* sqrt(2) * ( c1+c3+c5-c7) */
        tmp3 = MULTIPLY16(tmp3, FIX_1_501321110); /* sqrt(2) * ( c1+c3-c5-c7) */
        z1 = MULTIPLY16(z1, - FIX_0_899976223); /* sqrt(2) * (c7-c3) */
        z2 = MULTIPLY16(z2, - FIX_2_562915447); /* sqrt(2) * (-c1-c3) */
        z3 = MULTIPLY16(z3, - FIX_1_961570560); /* sqrt(2) * (-c3-c5) */
        z4 = MULTIPLY16(z4, - FIX_0_390180644); /* sqrt(2) * (c5-c3) */

        z3 += z5;
        z4 += z5;

        tmp0 += z1 + z3;
        tmp1 += z2 + z4;
        tmp2 += z2 + z3;
        tmp3 += z1 + z4;

        /* Final output stage: inputs are tmp10..tmp13, tmp0..tmp3 */

        outptr[0] = range_limit[(int) DESCALE(tmp10 + tmp3,
            CONST_BITS+PASS1_BITS+3) & RANGE_MASK];
        outptr[7] = range_limit[(int) DESCALE(tmp10 - tmp3,
            CONST_BITS+PASS1_BITS+3) & RANGE_MASK];
        outptr[1] = range_limit[(int) DESCALE(tmp11 + tmp2,
            CONST_BITS+PASS1_BITS+3) & RANGE_MASK];
        outptr[6] = range_limit[(int) DESCALE(tmp11 - tmp2,
            CONST_BITS+PASS1_BITS+3) & RANGE_MASK];
        outptr[2] = range_limit[(int) DESCALE(tmp12 + tmp1,
            CONST_BITS+PASS1_BITS+3) & RANGE_MASK];
        outptr[5] = range_limit[(int) DESCALE(tmp12 - tmp1,
            CONST_BITS+PASS1_BITS+3) & RANGE_MASK];
        outptr[3] = range_limit[(int) DESCALE(tmp13 + tmp0,
            CONST_BITS+PASS1_BITS+3) & RANGE_MASK];
        outptr[4] = range_limit[(int) DESCALE(tmp13 - tmp0,
            CONST_BITS+PASS1_BITS+3) & RANGE_MASK];

        wsptr += 8; /* advance pointer to next row */
    }
}



/* JPEG decoder implementation */


#define HUFF_LOOKAHEAD 8 /* # of bits of lookahead */

struct derived_tbl
{
    /* Basic tables: (element [0] of each array is unused) */
    long mincode[17]; /* smallest code of length k */
    long maxcode[18]; /* largest code of length k (-1 if none) */
    /* (maxcode[17] is a sentinel to ensure huff_DECODE terminates) */
    int valptr[17]; /* huffval[] index of 1st symbol of length k */

    /* Back link to public Huffman table (needed only in slow_DECODE) */
    int* pub;

    /* Lookahead tables: indexed by the next HUFF_LOOKAHEAD bits of
    the input data stream.  If the next Huffman code is no more
    than HUFF_LOOKAHEAD bits long, we can obtain its length and
    the corresponding symbol directly from these tables. */
    int look_nbits[1<<HUFF_LOOKAHEAD]; /* # bits, or 0 if too long */
    unsigned char look_sym[1<<HUFF_LOOKAHEAD]; /* symbol, or unused */
};

#define QUANT_TABLE_LENGTH  64

/* for type of Huffman table */
#define DC_LEN 28
#define AC_LEN 178

struct huffman_table
{   /* length and code according to JFIF format */
    int huffmancodes_dc[DC_LEN];
    int huffmancodes_ac[AC_LEN];
};

struct frame_component
{
    int ID;
    int horizontal_sampling;
    int vertical_sampling;
    int quanttable_select;
};

struct scan_component
{
    int ID;
    int DC_select;
    int AC_select;
};

struct bitstream
{
    unsigned long get_buffer; /* current bit-extraction buffer */
    int bits_left; /* # of unused bits in it */
    unsigned char* next_input_byte;
    unsigned char* input_end; /* upper limit +1 */
};

struct jpeg
{
    int x_size, y_size; /* size of image (can be less than block boundary) */
    int x_phys, y_phys; /* physical size, block aligned */
    int x_mbl; /* x dimension of MBL */
    int y_mbl; /* y dimension of MBL */
    int blocks; /* blocks per MBL */
    int restart_interval; /* number of MCUs between RSTm markers */
    int store_pos[4]; /* for Y block ordering */

    unsigned char* p_entropy_data;
    unsigned char* p_entropy_end;

    int quanttable[4][QUANT_TABLE_LENGTH]; /* raw quantization tables 0-3 */
    int qt_idct[2][QUANT_TABLE_LENGTH]; /* quantization tables for IDCT */

    struct huffman_table hufftable[2]; /* Huffman tables  */
    struct derived_tbl dc_derived_tbls[2]; /* Huffman-LUTs */
    struct derived_tbl ac_derived_tbls[2];

    struct frame_component frameheader[3]; /* Component descriptor */
    struct scan_component scanheader[3]; /* currently not used */

    int mcu_membership[6]; /* info per block */
    int tab_membership[6];
};


/* possible return flags for process_markers() */
#define HUFFTAB   0x0001 /* with huffman table */
#define QUANTTAB  0x0002 /* with quantization table */
#define APP0_JFIF 0x0004 /* with APP0 segment following JFIF standard */
#define FILL_FF   0x0008 /* with 0xFF padding bytes at begin/end */
#define SOF0      0x0010 /* with SOF0-Segment */
#define DHT       0x0020 /* with Definition of huffman tables */
#define SOS       0x0040 /* with Start-of-Scan segment */
#define DQT       0x0080 /* with definition of quantization table */

/* Preprocess the JPEG JFIF file */
int process_markers(unsigned char* p_src, long size, struct jpeg* p_jpeg)
{
    unsigned char* p_bytes = p_src;
    int marker_size; /* variable length of marker segment */
    int i, j, n;
    int ret = 0; /* returned flags */

    p_jpeg->p_entropy_end = p_src + size;

    while (p_src < p_bytes + size)
    {
        if (*p_src++ != 0xFF) /* no marker? */
        {
            p_src--; /* it's image data, put it back */
            p_jpeg->p_entropy_data = p_src;
            break; /* exit marker processing */
        }

        switch (*p_src++)
        {
        case 0xFF: /* Fill byte */
            ret |= FILL_FF;
        case 0x00: /* Zero stuffed byte - entropy data */
            p_src--; /* put it back */
            continue;

        case 0xC0: /* SOF Huff  - Baseline DCT */
            {
                ret |= SOF0;
                marker_size = *p_src++ << 8; /* Highbyte */
                marker_size |= *p_src++; /* Lowbyte */
                n = *p_src++; /* sample precision (= 8 or 12) */
                if (n != 8)
                {
                    return(-1); /* Unsupported sample precision */
                }
                p_jpeg->y_size = *p_src++ << 8; /* Highbyte */
                p_jpeg->y_size |= *p_src++; /* Lowbyte */
                p_jpeg->x_size = *p_src++ << 8; /* Highbyte */
                p_jpeg->x_size |= *p_src++; /* Lowbyte */

                n = (marker_size-2-6)/3;
                if (*p_src++ != n || (n != 1 && n != 3))
                {
                    return(-2); /* Unsupported SOF0 component specification */
                }
                for (i=0; i<n; i++)
                {
                    p_jpeg->frameheader[i].ID = *p_src++; /* Component info */
                    p_jpeg->frameheader[i].horizontal_sampling = *p_src >> 4;
                    p_jpeg->frameheader[i].vertical_sampling = *p_src++ & 0x0F;
                    p_jpeg->frameheader[i].quanttable_select = *p_src++;
                    if (p_jpeg->frameheader[i].horizontal_sampling > 2
                     || p_jpeg->frameheader[i].vertical_sampling > 2)
                    return -3; /* Unsupported SOF0 subsampling */
                }
                p_jpeg->blocks = n;
            }
            break;

        case 0xC1: /* SOF Huff  - Extended sequential DCT*/
        case 0xC2: /* SOF Huff  - Progressive DCT*/
        case 0xC3: /* SOF Huff  - Spatial (sequential) lossless*/
        case 0xC5: /* SOF Huff  - Differential sequential DCT*/
        case 0xC6: /* SOF Huff  - Differential progressive DCT*/
        case 0xC7: /* SOF Huff  - Differential spatial*/
        case 0xC8: /* SOF Arith - Reserved for JPEG extensions*/
        case 0xC9: /* SOF Arith - Extended sequential DCT*/
        case 0xCA: /* SOF Arith - Progressive DCT*/
        case 0xCB: /* SOF Arith - Spatial (sequential) lossless*/
        case 0xCD: /* SOF Arith - Differential sequential DCT*/
        case 0xCE: /* SOF Arith - Differential progressive DCT*/
        case 0xCF: /* SOF Arith - Differential spatial*/
            {
                return (-4); /* other DCT model than baseline not implemented */
            }

        case 0xC4: /* Define Huffman Table(s) */
            {
                unsigned char* p_temp;

                ret |= DHT;
                marker_size = *p_src++ << 8; /* Highbyte */
                marker_size |= *p_src++; /* Lowbyte */

                p_temp = p_src;
                while (p_src < p_temp+marker_size-2-17) /* another table */
                {
                    int sum = 0;
                    i = *p_src & 0x0F; /* table index */
                    if (i > 1)
                    {
                        return (-5); /* Huffman table index out of range */
                    }
                    else if (*p_src++ & 0xF0) /* AC table */
                    {
                        for (j=0; j<16; j++)
                        {
                            sum += *p_src;
                            p_jpeg->hufftable[i].huffmancodes_ac[j] = *p_src++;
                        }
                        if(16 + sum > AC_LEN)
                            return -10; /* longer than allowed */

                        for (; j < 16 + sum; j++)
                            p_jpeg->hufftable[i].huffmancodes_ac[j] = *p_src++;
                    }
                    else /* DC table */
                    {
                        for (j=0; j<16; j++)
                        {
                            sum += *p_src;
                            p_jpeg->hufftable[i].huffmancodes_dc[j] = *p_src++;
                        }
                        if(16 + sum > DC_LEN)
                            return -11; /* longer than allowed */

                        for (; j < 16 + sum; j++)
                            p_jpeg->hufftable[i].huffmancodes_dc[j] = *p_src++;
                    }
                } /* while */
                p_src = p_temp+marker_size - 2; // skip possible residue
            }
            break;

        case 0xCC: /* Define Arithmetic coding conditioning(s) */
            return(-6); /* Arithmetic coding not supported */

        case 0xD8: /* Start of Image */
        case 0xD9: /* End of Image */
        case 0x01: /* for temp private use arith code */
            break; /* skip parameterless marker */


        case 0xDA: /* Start of Scan */
            {
                ret |= SOS;
                marker_size = *p_src++ << 8; /* Highbyte */
                marker_size |= *p_src++; /* Lowbyte */

                n = (marker_size-2-1-3)/2;
                if (*p_src++ != n || (n != 1 && n != 3))
                {
                    return (-7); /* Unsupported SOS component specification */
                }
                for (i=0; i<n; i++)
                {
                    p_jpeg->scanheader[i].ID = *p_src++;
                    p_jpeg->scanheader[i].DC_select = *p_src >> 4;
                    p_jpeg->scanheader[i].AC_select = *p_src++ & 0x0F;
                }
                p_src += 3; /* skip spectral information */
            }
            break;

        case 0xDB: /* Define quantization Table(s) */
            {
                ret |= DQT;
                marker_size = *p_src++ << 8; /* Highbyte */
                marker_size |= *p_src++; /* Lowbyte */
                n = (marker_size-2)/(QUANT_TABLE_LENGTH+1); /* # of tables */
                for (i=0; i<n; i++)
                {
                    int id = *p_src++; /* ID */
                    if (id >= 4)
                    {
                        return (-8); /* Unsupported quantization table */
                    }
                    /* Read Quantisation table: */
                    for (j=0; j<QUANT_TABLE_LENGTH; j++)
                        p_jpeg->quanttable[id][j] = *p_src++;
                }
            }
            break;

        case 0xDD: /* Define Restart Interval */
            {
                marker_size = *p_src++ << 8; /* Highbyte */
                marker_size |= *p_src++; /* Lowbyte */
                p_jpeg->restart_interval = *p_src++ << 8; /* Highbyte */
                p_jpeg->restart_interval |= *p_src++; /* Lowbyte */
                p_src += marker_size-4; /* skip segment */
            }
            break;

        case 0xDC: /* Define Number of Lines */
        case 0xDE: /* Define Hierarchical progression */
        case 0xDF: /* Expand Reference Component(s) */
        case 0xE0: /* Application Field 0*/
        case 0xE1: /* Application Field 1*/
        case 0xE2: /* Application Field 2*/
        case 0xE3: /* Application Field 3*/
        case 0xE4: /* Application Field 4*/
        case 0xE5: /* Application Field 5*/
        case 0xE6: /* Application Field 6*/
        case 0xE7: /* Application Field 7*/
        case 0xE8: /* Application Field 8*/
        case 0xE9: /* Application Field 9*/
        case 0xEA: /* Application Field 10*/
        case 0xEB: /* Application Field 11*/
        case 0xEC: /* Application Field 12*/
        case 0xED: /* Application Field 13*/
        case 0xEE: /* Application Field 14*/
        case 0xEF: /* Application Field 15*/
        case 0xFE: /* Comment */
            {
                marker_size = *p_src++ << 8; /* Highbyte */
                marker_size |= *p_src++; /* Lowbyte */
                p_src += marker_size-2; /* skip segment */
            }
            break;

        case 0xF0: /* Reserved for JPEG extensions */
        case 0xF1: /* Reserved for JPEG extensions */
        case 0xF2: /* Reserved for JPEG extensions */
        case 0xF3: /* Reserved for JPEG extensions */
        case 0xF4: /* Reserved for JPEG extensions */
        case 0xF5: /* Reserved for JPEG extensions */
        case 0xF6: /* Reserved for JPEG extensions */
        case 0xF7: /* Reserved for JPEG extensions */
        case 0xF8: /* Reserved for JPEG extensions */
        case 0xF9: /* Reserved for JPEG extensions */
        case 0xFA: /* Reserved for JPEG extensions */
        case 0xFB: /* Reserved for JPEG extensions */
        case 0xFC: /* Reserved for JPEG extensions */
        case 0xFD: /* Reserved for JPEG extensions */
        case 0x02: /* Reserved */
        default:
            return (-9); /* Unknown marker */
        } /* switch */
    } /* while */

    return (ret); /* return flags with seen markers */
}


void default_huff_tbl(struct jpeg* p_jpeg)
{
    static const struct huffman_table luma_table =
    {
        {
            0x00,0x01,0x05,0x01,0x01,0x01,0x01,0x01,0x01,0x00,0x00,0x00,0x00,0x00,
            0x00,0x00,0x00,0x01,0x02,0x03,0x04,0x05,0x06,0x07,0x08,0x09,0x0A,0x0B
        },
        {
            0x00,0x02,0x01,0x03,0x03,0x02,0x04,0x03,0x05,0x05,0x04,0x04,0x00,0x00,0x01,0x7D,
            0x01,0x02,0x03,0x00,0x04,0x11,0x05,0x12,0x21,0x31,0x41,0x06,0x13,0x51,0x61,0x07,
            0x22,0x71,0x14,0x32,0x81,0x91,0xA1,0x08,0x23,0x42,0xB1,0xC1,0x15,0x52,0xD1,0xF0,
            0x24,0x33,0x62,0x72,0x82,0x09,0x0A,0x16,0x17,0x18,0x19,0x1A,0x25,0x26,0x27,0x28,
            0x29,0x2A,0x34,0x35,0x36,0x37,0x38,0x39,0x3A,0x43,0x44,0x45,0x46,0x47,0x48,0x49,
            0x4A,0x53,0x54,0x55,0x56,0x57,0x58,0x59,0x5A,0x63,0x64,0x65,0x66,0x67,0x68,0x69,
            0x6A,0x73,0x74,0x75,0x76,0x77,0x78,0x79,0x7A,0x83,0x84,0x85,0x86,0x87,0x88,0x89,
            0x8A,0x92,0x93,0x94,0x95,0x96,0x97,0x98,0x99,0x9A,0xA2,0xA3,0xA4,0xA5,0xA6,0xA7,
            0xA8,0xA9,0xAA,0xB2,0xB3,0xB4,0xB5,0xB6,0xB7,0xB8,0xB9,0xBA,0xC2,0xC3,0xC4,0xC5,
            0xC6,0xC7,0xC8,0xC9,0xCA,0xD2,0xD3,0xD4,0xD5,0xD6,0xD7,0xD8,0xD9,0xDA,0xE1,0xE2,
            0xE3,0xE4,0xE5,0xE6,0xE7,0xE8,0xE9,0xEA,0xF1,0xF2,0xF3,0xF4,0xF5,0xF6,0xF7,0xF8,
            0xF9,0xFA
        }
    };

    static const struct huffman_table chroma_table =
    {
        {
            0x00,0x03,0x01,0x01,0x01,0x01,0x01,0x01,0x01,0x01,0x01,0x00,0x00,0x00,
            0x00,0x00,0x00,0x01,0x02,0x03,0x04,0x05,0x06,0x07,0x08,0x09,0x0A,0x0B
        },
        {
            0x00,0x02,0x01,0x02,0x04,0x04,0x03,0x04,0x07,0x05,0x04,0x04,0x00,0x01,0x02,0x77,
            0x00,0x01,0x02,0x03,0x11,0x04,0x05,0x21,0x31,0x06,0x12,0x41,0x51,0x07,0x61,0x71,
            0x13,0x22,0x32,0x81,0x08,0x14,0x42,0x91,0xA1,0xB1,0xC1,0x09,0x23,0x33,0x52,0xF0,
            0x15,0x62,0x72,0xD1,0x0A,0x16,0x24,0x34,0xE1,0x25,0xF1,0x17,0x18,0x19,0x1A,0x26,
            0x27,0x28,0x29,0x2A,0x35,0x36,0x37,0x38,0x39,0x3A,0x43,0x44,0x45,0x46,0x47,0x48,
            0x49,0x4A,0x53,0x54,0x55,0x56,0x57,0x58,0x59,0x5A,0x63,0x64,0x65,0x66,0x67,0x68,
            0x69,0x6A,0x73,0x74,0x75,0x76,0x77,0x78,0x79,0x7A,0x82,0x83,0x84,0x85,0x86,0x87,
            0x88,0x89,0x8A,0x92,0x93,0x94,0x95,0x96,0x97,0x98,0x99,0x9A,0xA2,0xA3,0xA4,0xA5,
            0xA6,0xA7,0xA8,0xA9,0xAA,0xB2,0xB3,0xB4,0xB5,0xB6,0xB7,0xB8,0xB9,0xBA,0xC2,0xC3,
            0xC4,0xC5,0xC6,0xC7,0xC8,0xC9,0xCA,0xD2,0xD3,0xD4,0xD5,0xD6,0xD7,0xD8,0xD9,0xDA,
            0xE2,0xE3,0xE4,0xE5,0xE6,0xE7,0xE8,0xE9,0xEA,0xF2,0xF3,0xF4,0xF5,0xF6,0xF7,0xF8,
            0xF9,0xFA
        }
    };

    p_jpeg->hufftable[0] = luma_table;
    p_jpeg->hufftable[1] = chroma_table;

    return;
}

/* Compute the derived values for a Huffman table */
void fix_huff_tbl(int* htbl, struct derived_tbl* dtbl)
{
    int p, i, l, si;
    int lookbits, ctr;
    char huffsize[257];
    unsigned int huffcode[257];
    unsigned int code;

    dtbl->pub = htbl; /* fill in back link */

    /* Figure C.1: make table of Huffman code length for each symbol */
    /* Note that this is in code-length order. */

    p = 0;
    for (l = 1; l <= 16; l++)
    {    /* all possible code length */
        for (i = 1; i <= (int) htbl[l-1]; i++)  /* all codes per length */
            huffsize[p++] = (char) l;
    }
    huffsize[p] = 0;

    /* Figure C.2: generate the codes themselves */
    /* Note that this is in code-length order. */

    code = 0;
    si = huffsize[0];
    p = 0;
    while (huffsize[p])
    {
        while (((int) huffsize[p]) == si)
        {
            huffcode[p++] = code;
            code++;
        }
        code <<= 1;
        si++;
    }

    /* Figure F.15: generate decoding tables for bit-sequential decoding */

    p = 0;
    for (l = 1; l <= 16; l++)
    {
        if (htbl[l-1])
        {
            dtbl->valptr[l] = p; /* huffval[] index of 1st symbol of code length l */
            dtbl->mincode[l] = huffcode[p]; /* minimum code of length l */
            p += htbl[l-1];
            dtbl->maxcode[l] = huffcode[p-1]; /* maximum code of length l */
        }
        else
        {
            dtbl->maxcode[l] = -1;  /* -1 if no codes of this length */
        }
    }
    dtbl->maxcode[17] = 0xFFFFFL; /* ensures huff_DECODE terminates */

    /* Compute lookahead tables to speed up decoding.
    * First we set all the table entries to 0, indicating "too long";
    * then we iterate through the Huffman codes that are short enough and
    * fill in all the entries that correspond to bit sequences starting
    * with that code.
    */

    MEMSET(dtbl->look_nbits, 0, sizeof(dtbl->look_nbits));

    p = 0;
    for (l = 1; l <= HUFF_LOOKAHEAD; l++)
    {
        for (i = 1; i <= (int) htbl[l-1]; i++, p++)
        {
            /* l = current code's length, p = its index in huffcode[] & huffval[]. */
            /* Generate left-justified code followed by all possible bit sequences */
            lookbits = huffcode[p] << (HUFF_LOOKAHEAD-l);
            for (ctr = 1 << (HUFF_LOOKAHEAD-l); ctr > 0; ctr--)
            {
                dtbl->look_nbits[lookbits] = l;
                dtbl->look_sym[lookbits] = htbl[16+p];
                lookbits++;
            }
        }
    }
}


/* zag[i] is the natural-order position of the i'th element of zigzag order.
 * If the incoming data is corrupted, decode_mcu could attempt to
 * reference values beyond the end of the array.  To avoid a wild store,
 * we put some extra zeroes after the real entries.
 */
static const int zag[] =
{
     0,  1,  8, 16,  9,  2,  3, 10,
    17, 24, 32, 25, 18, 11,  4,  5,
    12, 19, 26, 33, 40, 48, 41, 34,
    27, 20, 13,  6,  7, 14, 21, 28,
    35, 42, 49, 56, 57, 50, 43, 36,
    29, 22, 15, 23, 30, 37, 44, 51,
    58, 59, 52, 45, 38, 31, 39, 46,
    53, 60, 61, 54, 47, 55, 62, 63,
     0,  0,  0,  0,  0,  0,  0,  0, /* extra entries in case k>63 below */
     0,  0,  0,  0,  0,  0,  0,  0
};

void build_lut(struct jpeg* p_jpeg)
{
    int i;
    fix_huff_tbl(p_jpeg->hufftable[0].huffmancodes_dc,
        &p_jpeg->dc_derived_tbls[0]);
    fix_huff_tbl(p_jpeg->hufftable[0].huffmancodes_ac,
        &p_jpeg->ac_derived_tbls[0]);
    fix_huff_tbl(p_jpeg->hufftable[1].huffmancodes_dc,
        &p_jpeg->dc_derived_tbls[1]);
    fix_huff_tbl(p_jpeg->hufftable[1].huffmancodes_ac,
        &p_jpeg->ac_derived_tbls[1]);

    /* build the dequantization tables for the IDCT (De-ZiZagged) */
    for (i=0; i<64; i++)
    {
        p_jpeg->qt_idct[0][zag[i]] = p_jpeg->quanttable[0][i];
        p_jpeg->qt_idct[1][zag[i]] = p_jpeg->quanttable[1][i];
    }

    for (i=0; i<4; i++)
        p_jpeg->store_pos[i] = i; /* default ordering */
    
    /* assignments for the decoding of blocks */
    if (p_jpeg->frameheader[0].horizontal_sampling == 2
        && p_jpeg->frameheader[0].vertical_sampling == 1)
    {   /* 4:2:2 */
        p_jpeg->blocks = 4;
        p_jpeg->x_mbl = (p_jpeg->x_size+15) / 16;
        p_jpeg->x_phys = p_jpeg->x_mbl * 16;
        p_jpeg->y_mbl = (p_jpeg->y_size+7) / 8;
        p_jpeg->y_phys = p_jpeg->y_mbl * 8;
        p_jpeg->mcu_membership[0] = 0; /* Y1=Y2=0, U=2, V=3 */
        p_jpeg->mcu_membership[1] = 0;
        p_jpeg->mcu_membership[2] = 2;
        p_jpeg->mcu_membership[3] = 3;
        p_jpeg->tab_membership[0] = 0; /* DC, DC, AC, AC */
        p_jpeg->tab_membership[1] = 0;
        p_jpeg->tab_membership[2] = 1;
        p_jpeg->tab_membership[3] = 1;
    }
    if (p_jpeg->frameheader[0].horizontal_sampling == 1
        && p_jpeg->frameheader[0].vertical_sampling == 2)
    {   /* 4:2:2 vertically subsampled */
        p_jpeg->store_pos[1] = 2; /* block positions are mirrored */
        p_jpeg->store_pos[2] = 1;
        p_jpeg->blocks = 4;
        p_jpeg->x_mbl = (p_jpeg->x_size+7) / 8;
        p_jpeg->x_phys = p_jpeg->x_mbl * 8;
        p_jpeg->y_mbl = (p_jpeg->y_size+15) / 16;
        p_jpeg->y_phys = p_jpeg->y_mbl * 16;
        p_jpeg->mcu_membership[0] = 0; /* Y1=Y2=0, U=2, V=3 */
        p_jpeg->mcu_membership[1] = 0;
        p_jpeg->mcu_membership[2] = 2;
        p_jpeg->mcu_membership[3] = 3;
        p_jpeg->tab_membership[0] = 0; /* DC, DC, AC, AC */
        p_jpeg->tab_membership[1] = 0;
        p_jpeg->tab_membership[2] = 1;
        p_jpeg->tab_membership[3] = 1;
    }
    else if (p_jpeg->frameheader[0].horizontal_sampling == 2
        && p_jpeg->frameheader[0].vertical_sampling == 2)
    {   /* 4:2:0 */
        p_jpeg->blocks = 6;
        p_jpeg->x_mbl = (p_jpeg->x_size+15) / 16;
        p_jpeg->x_phys = p_jpeg->x_mbl * 16;
        p_jpeg->y_mbl = (p_jpeg->y_size+15) / 16;
        p_jpeg->y_phys = p_jpeg->y_mbl * 16;
        p_jpeg->mcu_membership[0] = 0;
        p_jpeg->mcu_membership[1] = 0;
        p_jpeg->mcu_membership[2] = 0;
        p_jpeg->mcu_membership[3] = 0;
        p_jpeg->mcu_membership[4] = 2;
        p_jpeg->mcu_membership[5] = 3;
        p_jpeg->tab_membership[0] = 0;
        p_jpeg->tab_membership[1] = 0;
        p_jpeg->tab_membership[2] = 0;
        p_jpeg->tab_membership[3] = 0;
        p_jpeg->tab_membership[4] = 1;
        p_jpeg->tab_membership[5] = 1;
    }
    else if (p_jpeg->frameheader[0].horizontal_sampling == 1
        && p_jpeg->frameheader[0].vertical_sampling == 1)
    {   /* 4:4:4 */
        /* don't overwrite p_jpeg->blocks */
        p_jpeg->x_mbl = (p_jpeg->x_size+7) / 8;
        p_jpeg->x_phys = p_jpeg->x_mbl * 8;
        p_jpeg->y_mbl = (p_jpeg->y_size+7) / 8;
        p_jpeg->y_phys = p_jpeg->y_mbl * 8;
        p_jpeg->mcu_membership[0] = 0;
        p_jpeg->mcu_membership[1] = 2;
        p_jpeg->mcu_membership[2] = 3;
        p_jpeg->tab_membership[0] = 0;
        p_jpeg->tab_membership[1] = 1;
        p_jpeg->tab_membership[2] = 1;
    }

}


/*
* These functions/macros provide the in-line portion of bit fetching.
* Use check_bit_buffer to ensure there are N bits in get_buffer
* before using get_bits, peek_bits, or drop_bits.
*  check_bit_buffer(state,n,action);
*    Ensure there are N bits in get_buffer; if suspend, take action.
*  val = get_bits(n);
*    Fetch next N bits.
*  val = peek_bits(n);
*    Fetch next N bits without removing them from the buffer.
*  drop_bits(n);
*    Discard next N bits.
* The value N should be a simple variable, not an expression, because it
* is evaluated multiple times.
*/

INLINE void check_bit_buffer(struct bitstream* pb, int nbits)
{
    if (pb->bits_left < nbits)
    {   /* nbits is <= 16, so I can always refill 2 bytes in this case */
        unsigned char byte;

        byte = *pb->next_input_byte++;
        if (byte == 0xFF) /* legal marker can be byte stuffing or RSTm */
        {   /* simplification: just skip the (one-byte) marker code */
            pb->next_input_byte++;
        }
        pb->get_buffer = (pb->get_buffer << 8) | byte;

        byte = *pb->next_input_byte++;
        if (byte == 0xFF) /* legal marker can be byte stuffing or RSTm */
        {   /* simplification: just skip the (one-byte) marker code */
            pb->next_input_byte++;
        }
        pb->get_buffer = (pb->get_buffer << 8) | byte;
        
        pb->bits_left += 16;
    }
}

INLINE int get_bits(struct bitstream* pb, int nbits)
{
    return ((int) (pb->get_buffer >> (pb->bits_left -= nbits))) & ((1<<nbits)-1);
}

INLINE int peek_bits(struct bitstream* pb, int nbits)
{
    return ((int) (pb->get_buffer >> (pb->bits_left - nbits))) & ((1<<nbits)-1);
}

INLINE void drop_bits(struct bitstream* pb, int nbits)
{
    pb->bits_left -= nbits;
}

/* re-synchronize to entropy data (skip restart marker) */
void search_restart(struct bitstream* pb)
{
    pb->next_input_byte--; /* we may have overread it, taking 2 bytes */
    /* search for a non-byte-padding marker, has to be RSTm or EOS */
    while (pb->next_input_byte < pb->input_end &&
        (pb->next_input_byte[-2] != 0xFF || pb->next_input_byte[-1] == 0x00))
    {
        pb->next_input_byte++;
    }
    pb->bits_left = 0;
}

/* Figure F.12: extend sign bit. */
#define HUFF_EXTEND(x,s)  ((x) < extend_test[s] ? (x) + extend_offset[s] : (x))

static const int extend_test[16] =   /* entry n is 2**(n-1) */
{
    0, 0x0001, 0x0002, 0x0004, 0x0008, 0x0010, 0x0020, 0x0040, 0x0080,
    0x0100, 0x0200, 0x0400, 0x0800, 0x1000, 0x2000, 0x4000
};

static const int extend_offset[16] = /* entry n is (-1 << n) + 1 */
{
    0, ((-1)<<1) + 1, ((-1)<<2) + 1, ((-1)<<3) + 1, ((-1)<<4) + 1,
    ((-1)<<5) + 1, ((-1)<<6) + 1, ((-1)<<7) + 1, ((-1)<<8) + 1,
    ((-1)<<9) + 1, ((-1)<<10) + 1, ((-1)<<11) + 1, ((-1)<<12) + 1,
    ((-1)<<13) + 1, ((-1)<<14) + 1, ((-1)<<15) + 1
};

/* Decode a single value */
INLINE int huff_decode_dc(struct bitstream* bs, struct derived_tbl* tbl)
{
    int nb, look, s, r;

    check_bit_buffer(bs, HUFF_LOOKAHEAD);
    look = peek_bits(bs, HUFF_LOOKAHEAD);
    if ((nb = tbl->look_nbits[look]) != 0)
    {
        drop_bits(bs, nb);
        s = tbl->look_sym[look];
        check_bit_buffer(bs, s);
        r = get_bits(bs, s);
        s = HUFF_EXTEND(r, s);
    }
    else
    {   /*  slow_DECODE(s, HUFF_LOOKAHEAD+1)) < 0); */
        long code;
        nb=HUFF_LOOKAHEAD+1;
        check_bit_buffer(bs, nb);
        code = get_bits(bs, nb);
        while (code > tbl->maxcode[nb])
        {
            code <<= 1;
            check_bit_buffer(bs, 1);
            code |= get_bits(bs, 1);
            nb++;
        }
        if (nb > 16) /* error in Huffman */
        {
            s=0; /* fake a zero, this is most safe */
        }
        else
        {
            s = tbl->pub[16 + tbl->valptr[nb] + ((int) (code - tbl->mincode[nb])) ];
            check_bit_buffer(bs, s);
            r = get_bits(bs, s);
            s = HUFF_EXTEND(r, s);
        }
    } /* end slow decode */
    return s;
}

INLINE int huff_decode_ac(struct bitstream* bs, struct derived_tbl* tbl)
{
    int nb, look, s;

    check_bit_buffer(bs, HUFF_LOOKAHEAD);
    look = peek_bits(bs, HUFF_LOOKAHEAD);
    if ((nb = tbl->look_nbits[look]) != 0)
    {
        drop_bits(bs, nb);
        s = tbl->look_sym[look];
    }
    else
    {   /*  slow_DECODE(s, HUFF_LOOKAHEAD+1)) < 0); */
        long code;
        nb=HUFF_LOOKAHEAD+1;
        check_bit_buffer(bs, nb);
        code = get_bits(bs, nb);
        while (code > tbl->maxcode[nb])
        {
            code <<= 1;
            check_bit_buffer(bs, 1);
            code |= get_bits(bs, 1);
            nb++;
        }
        if (nb > 16) /* error in Huffman */
        {
            s=0; /* fake a zero, this is most safe */
        }
        else
        {
            s = tbl->pub[16 + tbl->valptr[nb] + ((int) (code - tbl->mincode[nb])) ];
        }
    } /* end slow decode */
    return s;
}


/* a JPEG decoder specialized in decoding only the luminance (b&w) */
int jpeg_decode(struct jpeg* p_jpeg, unsigned char* p_pixel, int downscale,
                void (*pf_progress)(int current, int total))
{
    struct bitstream bs; /* bitstream "object" */
    static int block[64]; /* decoded DCT coefficients */

    int width, height;
    int skip_line; /* bytes from one line to the next (skip_line) */
    int skip_strip, skip_mcu; /* bytes to next DCT row / column */

    int x, y; /* loop counter */

    unsigned char* p_byte; /* bitmap pointer */

    void (*pf_idct)(unsigned char*, int*, int*, int); /* selected IDCT */
    int k_need; /* AC coefficients needed up to here */
    int zero_need; /* init the block with this many zeros */

    int last_dc_val = 0;
    int store_offs[4]; /* memory offsets: order of Y11 Y12 Y21 Y22 U V */
    int restart = p_jpeg->restart_interval; /* MCUs until restart marker */

    /* pick the IDCT we want, determine how to work with coefs */
    if (downscale == 1)
    {
        pf_idct = idct8x8;
        k_need = 64; /* all */
        zero_need = 63; /* all */
    }
    else if (downscale == 2)
    {
        pf_idct = idct4x4;
        k_need = 25; /* this far in zig-zag to cover 4*4 */
        zero_need = 27; /* clear this far in linear order */
    }
    else if (downscale == 4)
    {
        pf_idct = idct2x2;
        k_need = 5; /* this far in zig-zag to cover 2*2 */
        zero_need = 9; /* clear this far in linear order */
    }
    else if (downscale == 8)
    {
        pf_idct = idct1x1;
        k_need = 0; /* no AC, not needed */
        zero_need = 0; /* no AC, not needed */
    }
    else return -1; /* not supported */

    /* init bitstream, fake a restart to make it start */
    bs.next_input_byte = p_jpeg->p_entropy_data;
    bs.bits_left = 0;
    bs.input_end = p_jpeg->p_entropy_end;

    width  = p_jpeg->x_phys / downscale;
    height = p_jpeg->y_phys / downscale;
    skip_line = width;
    skip_strip = skip_line * (height / p_jpeg->y_mbl);
    skip_mcu = (width/p_jpeg->x_mbl);

    /* prepare offsets about where to store the different blocks */
    store_offs[p_jpeg->store_pos[0]] = 0;
    store_offs[p_jpeg->store_pos[1]] = 8 / downscale; /* to the right */
    store_offs[p_jpeg->store_pos[2]] = width * 8 / downscale; /* below */
    store_offs[p_jpeg->store_pos[3]] = store_offs[1] + store_offs[2]; /* r+b */

    for(y=0; y<p_jpeg->y_mbl && bs.next_input_byte <= bs.input_end; y++)
    {
        p_byte = p_pixel;
        p_pixel += skip_strip;
        for (x=0; x<p_jpeg->x_mbl; x++)
        {
            int blkn;

            /* Outer loop handles each block in the MCU */
            for (blkn = 0; blkn < p_jpeg->blocks; blkn++)
            {   /* Decode a single block's worth of coefficients */
                int k = 1; /* coefficient index */
                int s, r; /* huffman values */
                int ci = p_jpeg->mcu_membership[blkn]; /* component index */
                int ti = p_jpeg->tab_membership[blkn]; /* table index */
                struct derived_tbl* dctbl = &p_jpeg->dc_derived_tbls[ti];
                struct derived_tbl* actbl = &p_jpeg->ac_derived_tbls[ti];

                /* Section F.2.2.1: decode the DC coefficient difference */
                s = huff_decode_dc(&bs, dctbl);

                if (ci == 0) /* only for Y component */
                {
                    last_dc_val += s;
                    block[0] = last_dc_val; /* output it (assumes zag[0] = 0) */

                    /* coefficient buffer must be cleared */
                    MEMSET(block+1, 0, zero_need*sizeof(block[0]));

                    /* Section F.2.2.2: decode the AC coefficients */
                    for (; k < k_need; k++)
                    {
                        s = huff_decode_ac(&bs, actbl);
                        r = s >> 4;
                        s &= 15;

                        if (s)
                        {
                            k += r;
                            check_bit_buffer(&bs, s);
                            r = get_bits(&bs, s);
                            block[zag[k]] = HUFF_EXTEND(r, s);
                        }
                        else
                        {
                            if (r != 15)
                            {
                                k = 64;
                                break;
                            }
                            k += r;
                        }
                    }  /* for k */
                }
                /* In this path we just discard the values */
                for (; k < 64; k++)
                {
                    s = huff_decode_ac(&bs, actbl);
                    r = s >> 4;
                    s &= 15;

                    if (s)
                    {
                        k += r;
                        check_bit_buffer(&bs, s);
                        drop_bits(&bs, s);
                    }
                    else
                    {
                        if (r != 15)
                            break;
                        k += r;
                    }
                }  /* for k */

                if (ci == 0)
                {   /* only for Y component */
                    pf_idct(p_byte+store_offs[blkn], block, p_jpeg->qt_idct[ti], 
                        skip_line);
                }
            } /* for blkn */
            p_byte += skip_mcu;
            if (p_jpeg->restart_interval && --restart == 0) 
            {   /* if a restart marker is due: */
                restart = p_jpeg->restart_interval; /* count again */
                search_restart(&bs); /* align the bitstream */
                last_dc_val = 0; /* reset decoder */
            }
        } /* for x */
        if (pf_progress != NULL)
            pf_progress(y, p_jpeg->y_mbl-1); /* notify about decoding progress */
    } /* for y */

    return 0; /* success */
}


/**************** end JPEG code ********************/



/**************** begin Application ********************/


/************************* Types ***************************/

struct t_disp
{
    unsigned char* bitmap;
    int width;
    int height;
    int stride;
    int x, y;
};


/************************* Globals ***************************/

/* decompressed image in the possible sizes (1,2,4,8), wasting the other */
struct t_disp disp[9];

/* my memory pool (from the mp3 buffer) */
char print[32]; /* use a common snprintf() buffer */
unsigned char* buf; /* up to here currently used by image(s) */
int buf_size;
unsigned char* buf_root; /* the root of the images */
int root_size;

/************************* Implementation ***************************/

#define ZOOM_IN  100 // return codes for below function
#define ZOOM_OUT 101

/* interactively scroll around the image */
int scroll_bmp(struct t_disp* pdisp)
{
    /*empty the button queue first, to avoid unwanted scrolling */
    while(rb->button_get(false) != BUTTON_NONE);

    while (true)
    {
        int button;
        int move;

        button = rb->button_get(true);

        if (button == SYS_USB_CONNECTED)
            return PLUGIN_USB_CONNECTED;

        switch(button & ~(BUTTON_REPEAT))
        {
        case BUTTON_LEFT:
            move = MIN(10, pdisp->x);
            if (move > 0)
            {
                gray_scroll_right(move, false); /* scroll right */
                pdisp->x -= move;
                gray_drawgraymap(
                    pdisp->bitmap + pdisp->y * pdisp->stride + pdisp->x,
                    0, MAX(0, (LCD_HEIGHT-pdisp->height)/2), // x, y
                    move, MIN(LCD_HEIGHT, pdisp->height), // w, h
                    pdisp->stride);
            }
            break;

        case BUTTON_RIGHT:
            move = MIN(10, pdisp->width - pdisp->x - LCD_WIDTH);
            if (move > 0)
            {
                gray_scroll_left(move, false); /* scroll left */
                pdisp->x += move;
                gray_drawgraymap(
                    pdisp->bitmap + pdisp->y * pdisp->stride + pdisp->x + LCD_WIDTH - move,
                    LCD_WIDTH - move, MAX(0, (LCD_HEIGHT-pdisp->height)/2), /* x, y */
                    move, MIN(LCD_HEIGHT, pdisp->height), /* w, h */
                    pdisp->stride);
            }
            break;

        case BUTTON_UP:
            move = MIN(8, pdisp->y);
            if (move > 0)
            {
                if (move == 8)
                    gray_scroll_down8(false); /* scroll down by 8 pixel */
                else
                    gray_scroll_down(move, false); /* scroll down 1..7 pixel */
                pdisp->y -= move;
                gray_drawgraymap(
                    pdisp->bitmap + pdisp->y * pdisp->stride + pdisp->x,
                    MAX(0, (LCD_WIDTH-pdisp->width)/2), 0, /* x, y */
                    MIN(LCD_WIDTH, pdisp->width), move, /* w, h */
                    pdisp->stride);
            }
            break;

        case BUTTON_DOWN:
            move = MIN(8, pdisp->height - pdisp->y - LCD_HEIGHT);
            if (move > 0)
            {
                if (move == 8)
                    gray_scroll_up8(false); /* scroll up by 8 pixel */
                else
                    gray_scroll_up(move, false); /* scroll up 1..7 pixel */
                pdisp->y += move;
                gray_drawgraymap(
                    pdisp->bitmap + (pdisp->y + LCD_HEIGHT - move) * pdisp->stride + pdisp->x,
                    MAX(0, (LCD_WIDTH-pdisp->width)/2), LCD_HEIGHT - move, /* x, y */
                    MIN(LCD_WIDTH, pdisp->width), move, /* w, h */
                    pdisp->stride);
            }
            break;

        case BUTTON_PLAY:
            return ZOOM_IN;
            break;

        case BUTTON_ON:
            return ZOOM_OUT;
            break;

        case BUTTON_OFF:
            return PLUGIN_OK;
        } /* switch */
    } /* while (true) */
}

/********************* main function *************************/

/* debug function */
int wait_for_button(void)
{
    int button;

    do
    {
        button = rb->button_get(true);
    } while ((button & BUTTON_REL) && button != SYS_USB_CONNECTED);

    return button;
}

/* callback updating a progress meter while JPEG decoding */
void cb_progess(int current, int total)
{
    rb->yield(); /* be nice to the other threads */
    rb->scrollbar(0, LCD_HEIGHT-8, LCD_WIDTH, 8, total, 0,
                  current, HORIZONTAL);
    rb->lcd_update_rect(0, LCD_HEIGHT-8, LCD_WIDTH, 8);
}

/* helper to align a buffer to a given power of two */
void align(unsigned char** ppbuf, int* plen, int align)
{
    unsigned int orig = (unsigned int)*ppbuf;
    unsigned int aligned = (orig + (align-1)) & ~(align-1);

    *plen -= aligned - orig;
    *ppbuf = (unsigned char*)aligned;
}


/* how far can we zoom in without running out of memory */
int min_downscale(int x, int y, int bufsize)
{
    int downscale = 8;

    if ((x/8) * (y/8) > bufsize)
        return 0; /* error, too large, even 1:8 doesn't fit */

    while ((x*2/downscale) * (y*2/downscale) < bufsize
        && downscale > 1)
    {
        downscale /= 2;
    }
    return downscale;
}


/* how far can we zoom out, to fit image into the LCD */
int max_downscale(int x, int y)
{
    int downscale = 1;

    while ((x/downscale > LCD_WIDTH || y/downscale > LCD_HEIGHT)
        && downscale < 8)
    {
        downscale *= 2;
    }

    return downscale;
}


/* return decoded or cached image */
struct t_disp* get_image(struct jpeg* p_jpg, int ds)
{
    int w, h; /* used to center output */
    int size; /* decompressed image size */
    long time; /* measured ticks */
    int status;

    struct t_disp* p_disp = &disp[ds]; /* short cut */

    if (p_disp->bitmap != NULL)
    {
        return p_disp; /* we still have it */
    }

    /* assign image buffer */

     /* physical size needed for decoding */
    size = (p_jpg->x_phys/ds) * (p_jpg->y_phys / ds);
    if (buf_size <= size)
    {   /* have to discard the current */
        int i;
        for (i=1; i<=8; i++)
            disp[i].bitmap = NULL; /* invalidate all bitmaps */
        buf = buf_root; /* start again from the beginning of the buffer */
        buf_size = root_size;
    }

    /* size may be less when decoded (if height is not block aligned) */
    size = (p_jpg->x_phys/ds) * (p_jpg->y_size / ds);
    p_disp->bitmap = buf;
    buf += size;
    buf_size -= size;

    rb->snprintf(print, sizeof(print), "decoding %d*%d",
        p_jpg->x_size/ds, p_jpg->y_size/ds);
    rb->lcd_puts(0, 3, print);
    rb->lcd_update();

    /* update image properties */
    p_disp->width = p_jpg->x_size/ds;
    p_disp->stride = p_jpg->x_phys / ds; /* use physical size for stride */
    p_disp->height = p_jpg->y_size/ds;

    /* the actual decoding */
    time = *rb->current_tick;
    status = jpeg_decode(p_jpg, p_disp->bitmap, ds, cb_progess);
    if (status)
    {
        rb->splash(HZ*2, true, "decode error %d", status);
        return NULL;
    }
    time = *rb->current_tick - time;
    rb->snprintf(print, sizeof(print), " %d.%02d sec ", time/HZ, time%HZ);
    rb->lcd_getstringsize(print, &w, &h); /* centered in progress bar */
    rb->lcd_putsxy((LCD_WIDTH - w)/2, LCD_HEIGHT - h, print);
    rb->lcd_update();

    return p_disp;
}


/* set the view to the given center point, limit if necessary */
void set_view (struct t_disp* p_disp, int cx, int cy)
{
    int x, y;

    /* plain center to available width/height */
    x = cx - MIN(LCD_WIDTH, p_disp->width) / 2;
    y = cy - MIN(LCD_HEIGHT, p_disp->height) / 2;

    /* limit against upper image size */
    x = MIN(p_disp->width - LCD_WIDTH, x);
    y = MIN(p_disp->height - LCD_HEIGHT, y);

    /* limit against negative side */
    x = MAX(0, x);
    y = MAX(0, y);

    p_disp->x = x; /* set the values */
    p_disp->y = y;
}


/* calculate the view center based on the bitmap position */
void get_view(struct t_disp* p_disp, int* p_cx, int* p_cy)
{
    *p_cx = p_disp->x + MIN(LCD_WIDTH, p_disp->width) / 2;
    *p_cy = p_disp->y + MIN(LCD_HEIGHT, p_disp->height) / 2;
}


/* load, decode, display the image */
int main(char* filename)
{
    int fd;
    int filesize;
    int grayscales;
    int graysize; // helper
    unsigned char* buf_jpeg; /* compressed JPEG image */
    static struct jpeg jpg; /* too large for stack */
    int status;
    int ds, ds_min, ds_max; /* scaling and limits */
    struct t_disp* p_disp; /* currenly displayed image */
    int cx, cy; /* view center */

    fd = rb->open(filename, O_RDONLY);
    if (fd < 0)
    {
        rb->splash(HZ*2, true, "fopen err");
        return PLUGIN_ERROR;
    }
    filesize = rb->filesize(fd);

    rb->memset(&disp, 0, sizeof(disp));

    buf = rb->plugin_get_mp3_buffer(&buf_size); /* start munching memory */


    /* initialize the grayscale buffer:
     * 112 pixels wide, 8 rows (64 pixels) high, (try to) reserve
     * 32 bitplanes for 33 shades of gray. (uses 28856 bytes)*/
    grayscales = gray_init_buffer(buf, buf_size, 112, 8, 32, &graysize) + 1;
    buf += graysize;
    buf_size -= graysize;
    if (grayscales < 33 || buf_size <= 0)
    {
        rb->splash(HZ*2, true, "gray buf error");
        return PLUGIN_ERROR;
    }


    /* allocate JPEG buffer */
    align(&buf, &buf_size, 2); /* 16 bit align */
    buf_jpeg = (unsigned char*)(((int)buf + 1) & ~1);
    buf += filesize;
    buf_size -= filesize;
    buf_root = buf; /* we can start the decompressed images behind it */
    root_size = buf_size;
    if (buf_size <= 0)
    {
        rb->splash(HZ*2, true, "out of memory");
        rb->close(fd);
        return PLUGIN_ERROR;
    }

    rb->snprintf(print, sizeof(print), "loading %d bytes", filesize);
    rb->lcd_puts(0, 0, print);
    rb->lcd_update();

    rb->read(fd, buf_jpeg, filesize);
    rb->close(fd);

    rb->snprintf(print, sizeof(print), "decoding markers");
    rb->lcd_puts(0, 1, print);
    rb->lcd_update();

    rb->memset(&jpg, 0, sizeof(jpg)); /* clear info struct */
    /* process markers, unstuffing */
    status = process_markers(buf_jpeg, filesize, &jpg);
    if (status < 0 || (status & (DQT | SOF0)) != (DQT | SOF0))
    {   /* bad format or minimum components not contained */
        rb->splash(HZ*2, true, "unsupported %d", status);
        return PLUGIN_ERROR;
    }
    if (!(status & DHT)) /* if no Huffman table present: */
        default_huff_tbl(&jpg); /* use default */
    build_lut(&jpg); /* derive Huffman and other lookup-tables */

    rb->snprintf(print, sizeof(print), "image %d*%d", jpg.x_size, jpg.y_size);
    rb->lcd_puts(0, 2, print);
    rb->lcd_update();

    /* check display constraint */
    ds_max = max_downscale(jpg.x_size, jpg.y_size);
    /* check memory constraint */
    ds_min = min_downscale(jpg.x_phys, jpg.y_phys, buf_size);
    if (ds_min == 0)
    {
        rb->splash(HZ*2, true, "too large");
        return PLUGIN_ERROR;
    }
    ds = ds_max; /* initials setting */
    cx = jpg.x_size/ds/2; /* center the view */
    cy = jpg.y_size/ds/2;

    do  /* loop the image prepare and decoding when zoomed */
    {
        p_disp = get_image(&jpg, ds); /* decode or fetch from cache */
        if (p_disp == NULL)
            return PLUGIN_ERROR;

        set_view(p_disp, cx, cy);

        rb->snprintf(print, sizeof(print), "showing %d*%d",
            p_disp->width, p_disp->height);
        rb->lcd_puts(0, 3, print);
        rb->lcd_update();

        gray_clear_display();
        gray_drawgraymap(
            p_disp->bitmap + p_disp->y * p_disp->stride + p_disp->x,
            MAX(0, (LCD_WIDTH - p_disp->width) / 2),
            MAX(0, (LCD_HEIGHT - p_disp->height) / 2),
            MIN(LCD_WIDTH, p_disp->width),
            MIN(LCD_HEIGHT, p_disp->height),
            p_disp->stride);

        gray_show_display(true); /* switch on grayscale overlay */

        /* drawing is now finished, play around with scrolling
         * until you press OFF or connect USB
         */
        while (1)
        {
            status = scroll_bmp(p_disp);
            if (status == ZOOM_IN)
            {
                if (ds > ds_min)
                {
                    ds /= 2; /* reduce downscaling to zoom in */
                    get_view(p_disp, &cx, &cy);
                    cx *= 2; /* prepare the position in the new image */
                    cy *= 2;
                }
                else
                    continue;
            }

            if (status == ZOOM_OUT)
            {
                if (ds < ds_max)
                {
                    ds *= 2; /* increase downscaling to zoom out */
                    get_view(p_disp, &cx, &cy);
                    cx /= 2; /* prepare the position in the new image */
                    cy /= 2;
                }
                else
                    continue;
            }
            break;
        }

        gray_show_display(false); /* switch off overlay */

    }
    while (status != PLUGIN_OK && status != PLUGIN_USB_CONNECTED);

    gray_release_buffer(); /* deinitialize */

    return status;
}

/******************** Plugin entry point *********************/

enum plugin_status plugin_start(struct plugin_api* api, void* parameter)
{
    int ret;
    /* this macro should be called as the first thing you do in the plugin.
    it test that the api version and model the plugin was compiled for
    matches the machine it is running on */
    TEST_PLUGIN_API(api);

    rb = api; /* copy to global api pointer */

    /* This plugin uses the grayscale framework, so initialize */
    gray_init(api);
    ret = main((char*)parameter);

    if (ret == PLUGIN_USB_CONNECTED)
        rb->usb_screen();
    return ret;
}

#endif /* #ifdef HAVE_LCD_BITMAP */
#endif /* #ifndef SIMULATOR */