/* * Range coder * Copyright (c) 2004 Michael Niedermayer <michaelni@gmx.at> * * This file is part of FFmpeg. * * FFmpeg 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 2.1 of the License, or (at your option) any later version. * * FFmpeg 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 FFmpeg; if not, write to the Free Software * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA */ /** * @file * Range coder. * based upon * "Range encoding: an algorithm for removing redundancy from a digitised * message. * G. N. N. Martin Presented in March 1979 to the Video & * Data Recording Conference, * IBM UK Scientific Center held in Southampton July 24-27 1979." */ #include <string.h> #include "libavutil/attributes.h" #include "libavutil/avassert.h" #include "libavutil/intreadwrite.h" #include "avcodec.h" #include "rangecoder.h" av_cold void ff_init_range_encoder(RangeCoder *c, uint8_t *buf, int buf_size) { c->bytestream_start = c->bytestream = buf; c->bytestream_end = buf + buf_size; c->low = 0; c->range = 0xFF00; c->outstanding_count = 0; c->outstanding_byte = -1; } av_cold void ff_init_range_decoder(RangeCoder *c, const uint8_t *buf, int buf_size) { /* cast to avoid compiler warning */ ff_init_range_encoder(c, (uint8_t *)buf, buf_size); c->low = AV_RB16(c->bytestream); c->bytestream += 2; c->overread = 0; if (c->low >= 0xFF00) { c->low = 0xFF00; c->bytestream_end = c->bytestream; } } void ff_build_rac_states(RangeCoder *c, int factor, int max_p) { const int64_t one = 1LL << 32; int64_t p; int last_p8, p8, i; memset(c->zero_state, 0, sizeof(c->zero_state)); memset(c->one_state, 0, sizeof(c->one_state)); last_p8 = 0; p = one / 2; for (i = 0; i < 128; i++) { p8 = (256 * p + one / 2) >> 32; // FIXME: try without the one if (p8 <= last_p8) p8 = last_p8 + 1; if (last_p8 && last_p8 < 256 && p8 <= max_p) c->one_state[last_p8] = p8; p += ((one - p) * factor + one / 2) >> 32; last_p8 = p8; } for (i = 256 - max_p; i <= max_p; i++) { if (c->one_state[i]) continue; p = (i * one + 128) >> 8; p += ((one - p) * factor + one / 2) >> 32; p8 = (256 * p + one / 2) >> 32; // FIXME: try without the one if (p8 <= i) p8 = i + 1; if (p8 > max_p) p8 = max_p; c->one_state[i] = p8; } for (i = 1; i < 255; i++) c->zero_state[i] = 256 - c->one_state[256 - i]; } /* Return the number of bytes written. */ int ff_rac_terminate(RangeCoder *c) { c->range = 0xFF; c->low += 0xFF; renorm_encoder(c); c->range = 0xFF; renorm_encoder(c); av_assert1(c->low == 0); av_assert1(c->range >= 0x100); return c->bytestream - c->bytestream_start; }