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/*
* FFv1 codec
*
* Copyright (c) 2024 Lynne <dev@lynne.ee>
*
* 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
*/
#define VLC_STATE_SIZE 8
layout(buffer_reference, buffer_reference_align = VLC_STATE_SIZE) buffer VlcState {
uint32_t error_sum;
int16_t drift;
int8_t bias;
uint8_t count;
};
void update_vlc_state(inout VlcState state, const int v)
{
int drift = state.drift;
int count = state.count;
int bias = state.bias;
state.error_sum += uint16_t(abs(v));
drift += v;
if (count == 128) { // FIXME: variable
count >>= 1;
drift >>= 1;
state.error_sum >>= 1;
}
count++;
if (drift <= -count) {
bias = max(bias - 1, -128);
drift = max(drift + count, -count + 1);
} else if (drift > 0) {
bias = min(bias + 1, 127);
drift = min(drift - count, 0);
}
state.bias = int8_t(bias);
state.drift = int16_t(drift);
state.count = uint8_t(count);
}
struct Symbol {
uint32_t bits;
uint32_t val;
};
Symbol set_ur_golomb(int i, int k, int limit, int esc_len)
{
int e;
Symbol sym;
#ifdef DEBUG
if (i < 0)
debugPrintfEXT("Error: i is zero!");
#endif
e = i >> k;
if (e < limit) {
sym.bits = e + k + 1;
sym.val = (1 << k) + zero_extend(i, k);
} else {
sym.bits = limit + esc_len;
sym.val = i - limit + 1;
}
return sym;
}
/**
* write signed golomb rice code (ffv1).
*/
Symbol set_sr_golomb(int i, int k, int limit, int esc_len)
{
int v;
v = -2 * i - 1;
v ^= (v >> 31);
return set_ur_golomb(v, k, limit, esc_len);
}
Symbol get_vlc_symbol(inout VlcState state, int v, int bits)
{
int i, k, code;
Symbol sym;
v = fold(v - int(state.bias), bits);
i = state.count;
k = 0;
while (i < state.error_sum) { // FIXME: optimize
k++;
i += i;
}
#ifdef DEBUG
if (k > 16)
debugPrintfEXT("Error: k > 16!");
#endif
code = v ^ ((2 * state.drift + state.count) >> 31);
update_vlc_state(state, v);
return set_sr_golomb(code, k, 12, bits);
}
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