yading@10: /*
yading@10:  * Range coder
yading@10:  * Copyright (c) 2004 Michael Niedermayer <michaelni@gmx.at>
yading@10:  *
yading@10:  * This file is part of FFmpeg.
yading@10:  *
yading@10:  * FFmpeg is free software; you can redistribute it and/or
yading@10:  * modify it under the terms of the GNU Lesser General Public
yading@10:  * License as published by the Free Software Foundation; either
yading@10:  * version 2.1 of the License, or (at your option) any later version.
yading@10:  *
yading@10:  * FFmpeg is distributed in the hope that it will be useful,
yading@10:  * but WITHOUT ANY WARRANTY; without even the implied warranty of
yading@10:  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
yading@10:  * Lesser General Public License for more details.
yading@10:  *
yading@10:  * You should have received a copy of the GNU Lesser General Public
yading@10:  * License along with FFmpeg; if not, write to the Free Software
yading@10:  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
yading@10:  */
yading@10: 
yading@10: /**
yading@10:  * @file
yading@10:  * Range coder.
yading@10:  * based upon
yading@10:  *    "Range encoding: an algorithm for removing redundancy from a digitised
yading@10:  *                     message.
yading@10:  *     G. N. N. Martin                  Presented in March 1979 to the Video &
yading@10:  *                                      Data Recording Conference,
yading@10:  *     IBM UK Scientific Center         held in Southampton July 24-27 1979."
yading@10:  *
yading@10:  */
yading@10: 
yading@10: #include <string.h>
yading@10: 
yading@10: #include "libavutil/avassert.h"
yading@10: #include "avcodec.h"
yading@10: #include "rangecoder.h"
yading@10: #include "bytestream.h"
yading@10: 
yading@10: void ff_init_range_encoder(RangeCoder *c, uint8_t *buf, int buf_size)
yading@10: {
yading@10:     c->bytestream_start  =
yading@10:     c->bytestream        = buf;
yading@10:     c->bytestream_end    = buf + buf_size;
yading@10:     c->low               = 0;
yading@10:     c->range             = 0xFF00;
yading@10:     c->outstanding_count = 0;
yading@10:     c->outstanding_byte  = -1;
yading@10: }
yading@10: 
yading@10: void ff_init_range_decoder(RangeCoder *c, const uint8_t *buf, int buf_size)
yading@10: {
yading@10:     /* cast to avoid compiler warning */
yading@10:     ff_init_range_encoder(c, (uint8_t *)buf, buf_size);
yading@10: 
yading@10:     c->low = bytestream_get_be16((const uint8_t **)&c->bytestream);
yading@10: }
yading@10: 
yading@10: void ff_build_rac_states(RangeCoder *c, int factor, int max_p)
yading@10: {
yading@10:     const int64_t one = 1LL << 32;
yading@10:     int64_t p;
yading@10:     int last_p8, p8, i;
yading@10: 
yading@10:     memset(c->zero_state, 0, sizeof(c->zero_state));
yading@10:     memset(c->one_state, 0, sizeof(c->one_state));
yading@10: 
yading@10:     last_p8 = 0;
yading@10:     p       = one / 2;
yading@10:     for (i = 0; i < 128; i++) {
yading@10:         p8 = (256 * p + one / 2) >> 32; // FIXME: try without the one
yading@10:         if (p8 <= last_p8)
yading@10:             p8 = last_p8 + 1;
yading@10:         if (last_p8 && last_p8 < 256 && p8 <= max_p)
yading@10:             c->one_state[last_p8] = p8;
yading@10: 
yading@10:         p      += ((one - p) * factor + one / 2) >> 32;
yading@10:         last_p8 = p8;
yading@10:     }
yading@10: 
yading@10:     for (i = 256 - max_p; i <= max_p; i++) {
yading@10:         if (c->one_state[i])
yading@10:             continue;
yading@10: 
yading@10:         p  = (i * one + 128) >> 8;
yading@10:         p += ((one - p) * factor + one / 2) >> 32;
yading@10:         p8 = (256 * p + one / 2) >> 32; // FIXME: try without the one
yading@10:         if (p8 <= i)
yading@10:             p8 = i + 1;
yading@10:         if (p8 > max_p)
yading@10:             p8 = max_p;
yading@10:         c->one_state[i] = p8;
yading@10:     }
yading@10: 
yading@10:     for (i = 1; i < 255; i++)
yading@10:         c->zero_state[i] = 256 - c->one_state[256 - i];
yading@10: }
yading@10: 
yading@10: /* Return the number of bytes written. */
yading@10: int ff_rac_terminate(RangeCoder *c)
yading@10: {
yading@10:     c->range = 0xFF;
yading@10:     c->low  += 0xFF;
yading@10:     renorm_encoder(c);
yading@10:     c->range = 0xFF;
yading@10:     renorm_encoder(c);
yading@10: 
yading@10:     av_assert1(c->low   == 0);
yading@10:     av_assert1(c->range >= 0x100);
yading@10: 
yading@10:     return c->bytestream - c->bytestream_start;
yading@10: }
yading@10: 
yading@10: #ifdef TEST
yading@10: #define SIZE 10240
yading@10: 
yading@10: #include "libavutil/lfg.h"
yading@10: #include "libavutil/log.h"
yading@10: 
yading@10: int main(void)
yading@10: {
yading@10:     RangeCoder c;
yading@10:     uint8_t b[9 * SIZE];
yading@10:     uint8_t r[9 * SIZE];
yading@10:     int i;
yading@10:     uint8_t state[10];
yading@10:     AVLFG prng;
yading@10: 
yading@10:     av_lfg_init(&prng, 1);
yading@10: 
yading@10:     ff_init_range_encoder(&c, b, SIZE);
yading@10:     ff_build_rac_states(&c, 0.05 * (1LL << 32), 128 + 64 + 32 + 16);
yading@10: 
yading@10:     memset(state, 128, sizeof(state));
yading@10: 
yading@10:     for (i = 0; i < SIZE; i++)
yading@10:         r[i] = av_lfg_get(&prng) % 7;
yading@10: 
yading@10:     for (i = 0; i < SIZE; i++)
yading@10:         put_rac(&c, state, r[i] & 1);
yading@10: 
yading@10:     ff_rac_terminate(&c);
yading@10: 
yading@10:     ff_init_range_decoder(&c, b, SIZE);
yading@10: 
yading@10:     memset(state, 128, sizeof(state));
yading@10: 
yading@10:     for (i = 0; i < SIZE; i++)
yading@10:         if ((r[i] & 1) != get_rac(&c, state)) {
yading@10:             av_log(NULL, AV_LOG_ERROR, "rac failure at %d\n", i);
yading@10:             return 1;
yading@10:         }
yading@10: 
yading@10:     return 0;
yading@10: }
yading@10: #endif /* TEST */