rockbox/apps/codecs/libffmpegFLAC/golomb.h

/*
 * exp golomb vlc stuff
 * Copyright (c) 2003 Michael Niedermayer <michaelni@gmx.at>
 * Copyright (c) 2004 Alex Beregszaszi
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2 of the License, or (at your option) any later version.
 *
 * This library is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 *
 */

#include <limits.h>

/* From libavutil/common.h */
extern const uint8_t ff_log2_tab[256];

static inline int av_log2(unsigned int v)
{
    int n;

    n = 0;
    if (v & 0xffff0000) {
        v >>= 16;
        n += 16;
    }
    if (v & 0xff00) {
        v >>= 8;
        n += 8;
    }
    n += ff_log2_tab[v];

    return n;
}

/**
 * @file golomb.h
 * @brief 
 *     exp golomb vlc stuff
 * @author Michael Niedermayer <michaelni@gmx.at> and Alex Beregszaszi
 */

 
/**
 * read unsigned golomb rice code (jpegls).
 */
static inline int get_ur_golomb_jpegls(GetBitContext *gb, int k, int limit, int esc_len){
    unsigned int buf;
    int log;
    
    OPEN_READER(re, gb);
    UPDATE_CACHE(re, gb);
    buf=GET_CACHE(re, gb);

    log= av_log2(buf);
    
    if(log > 31-11){
        buf >>= log - k;
        buf += (30-log)<<k;
        LAST_SKIP_BITS(re, gb, 32 + k - log);
        CLOSE_READER(re, gb);
    
        return buf;
    }else{
        int i;
        for(i=0; SHOW_UBITS(re, gb, 1) == 0; i++){
            LAST_SKIP_BITS(re, gb, 1);
            UPDATE_CACHE(re, gb);
        }
        SKIP_BITS(re, gb, 1);

        if(i < limit - 1){
            if(k){
                buf = SHOW_UBITS(re, gb, k);
                LAST_SKIP_BITS(re, gb, k);
            }else{
                buf=0;
            }

            CLOSE_READER(re, gb);
            return buf + (i<<k);
        }else if(i == limit - 1){
            buf = SHOW_UBITS(re, gb, esc_len);
            LAST_SKIP_BITS(re, gb, esc_len);
            CLOSE_READER(re, gb);
    
            return buf + 1;
        }else
            return -1;
    }
}

/**
 * read signed golomb rice code (flac).
 */
static inline int get_sr_golomb_flac(GetBitContext *gb, int k, int limit, int esc_len){
    int v= get_ur_golomb_jpegls(gb, k, limit, esc_len);
    return (v>>1) ^ -(v&1);
}

/**
 * read unsigned golomb rice code (shorten).
 */
#define get_ur_golomb_shorten(gb, k) get_ur_golomb_jpegls(gb, k, INT_MAX, 0)
/*
static inline unsigned int get_ur_golomb_shorten(GetBitContext *gb, int k){
	return get_ur_golomb_jpegls(gb, k, INT_MAX, 0);
}
*/

/**
 * read signed golomb rice code (shorten).
 */
static inline int get_sr_golomb_shorten(GetBitContext* gb, int k)
{
    int uvar = get_ur_golomb_jpegls(gb, k + 1, INT_MAX, 0);
    if (uvar & 1)
        return ~(uvar >> 1);
    else
        return uvar >> 1;
}