5ba289bc27
git-svn-id: svn://svn.rockbox.org/rockbox/trunk@12204 a1c6a512-1295-4272-9138-f99709370657
138 lines
4.2 KiB
C
138 lines
4.2 KiB
C
/***************************************************************************
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* __________ __ ___.
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* Open \______ \ ____ ____ | | _\_ |__ _______ ___
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* Source | _// _ \_/ ___\| |/ /| __ \ / _ \ \/ /
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* Jukebox | | ( <_> ) \___| < | \_\ ( <_> > < <
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* Firmware |____|_ /\____/ \___ >__|_ \|___ /\____/__/\_ \
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* \/ \/ \/ \/ \/
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* $Id$
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*
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* Copyright (C) 2006 Jens Arnold
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*
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* Fixed point library for plugins
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*
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* All files in this archive are subject to the GNU General Public License.
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* See the file COPYING in the source tree root for full license agreement.
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*
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* This software is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY
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* KIND, either express or implied.
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*
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****************************************************************************/
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#include <inttypes.h>
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/* Inverse gain of circular cordic rotation in s0.31 format. */
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static const long cordic_circular_gain = 0xb2458939; /* 0.607252929 */
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/* Table of values of atan(2^-i) in 0.32 format fractions of pi where pi = 0xffffffff / 2 */
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static const unsigned long atan_table[] = {
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0x1fffffff, /* +0.785398163 (or pi/4) */
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0x12e4051d, /* +0.463647609 */
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0x09fb385b, /* +0.244978663 */
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0x051111d4, /* +0.124354995 */
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0x028b0d43, /* +0.062418810 */
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0x0145d7e1, /* +0.031239833 */
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0x00a2f61e, /* +0.015623729 */
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0x00517c55, /* +0.007812341 */
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0x0028be53, /* +0.003906230 */
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0x00145f2e, /* +0.001953123 */
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0x000a2f98, /* +0.000976562 */
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0x000517cc, /* +0.000488281 */
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0x00028be6, /* +0.000244141 */
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0x000145f3, /* +0.000122070 */
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0x0000a2f9, /* +0.000061035 */
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0x0000517c, /* +0.000030518 */
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0x000028be, /* +0.000015259 */
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0x0000145f, /* +0.000007629 */
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0x00000a2f, /* +0.000003815 */
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0x00000517, /* +0.000001907 */
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0x0000028b, /* +0.000000954 */
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0x00000145, /* +0.000000477 */
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0x000000a2, /* +0.000000238 */
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0x00000051, /* +0.000000119 */
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0x00000028, /* +0.000000060 */
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0x00000014, /* +0.000000030 */
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0x0000000a, /* +0.000000015 */
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0x00000005, /* +0.000000007 */
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0x00000002, /* +0.000000004 */
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0x00000001, /* +0.000000002 */
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0x00000000, /* +0.000000001 */
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0x00000000, /* +0.000000000 */
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};
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/**
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* Implements sin and cos using CORDIC rotation.
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*
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* @param phase has range from 0 to 0xffffffff, representing 0 and
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* 2*pi respectively.
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* @param cos return address for cos
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* @return sin of phase, value is a signed value from LONG_MIN to LONG_MAX,
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* representing -1 and 1 respectively.
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*/
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long fsincos(unsigned long phase, long *cos)
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{
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int32_t x, x1, y, y1;
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unsigned long z, z1;
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int i;
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/* Setup initial vector */
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x = cordic_circular_gain;
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y = 0;
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z = phase;
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/* The phase has to be somewhere between 0..pi for this to work right */
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if (z < 0xffffffff / 4) {
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/* z in first quadrant, z += pi/2 to correct */
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x = -x;
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z += 0xffffffff / 4;
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} else if (z < 3 * (0xffffffff / 4)) {
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/* z in third quadrant, z -= pi/2 to correct */
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z -= 0xffffffff / 4;
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} else {
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/* z in fourth quadrant, z -= 3pi/2 to correct */
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x = -x;
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z -= 3 * (0xffffffff / 4);
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}
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/* Each iteration adds roughly 1-bit of extra precision */
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for (i = 0; i < 31; i++) {
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x1 = x >> i;
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y1 = y >> i;
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z1 = atan_table[i];
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/* Decided which direction to rotate vector. Pivot point is pi/2 */
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if (z >= 0xffffffff / 4) {
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x -= y1;
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y += x1;
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z -= z1;
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} else {
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x += y1;
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y -= x1;
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z += z1;
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}
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}
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if (cos)
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*cos = x;
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return y;
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}
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/**
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* Fixed point square root via Newton-Raphson.
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* @param a square root argument.
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* @param fracbits specifies number of fractional bits in argument.
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* @return Square root of argument in same fixed point format as input.
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*/
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long fsqrt(long a, unsigned int fracbits)
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{
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long b = a/2 + (1 << fracbits); /* initial approximation */
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unsigned n;
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const unsigned iterations = 4;
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for (n = 0; n < iterations; ++n)
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b = (b + (long)(((long long)(a) << fracbits)/b))/2;
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return b;
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}
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