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130 lines
2.2 KiB
C
130 lines
2.2 KiB
C
#ifndef __GOLOMB_H
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#define __GOLOMB_H
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#include "bitcoder.h"
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static inline unsigned int
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required_bits (unsigned int x)
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{
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int bits = 31;
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while ((x & (1 << bits)) == 0 && bits)
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bits--;
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return bits;
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}
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static inline void
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write_number_binary (BitCoderState * b, unsigned int x, int bits, int u)
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{
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/*printf ("wrote %i with %i bits (%i+%i)\n", x, u+bits, u, bits); */
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while (bits) {
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bits--;
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bitcoder_write_bit (b, (x >> bits) & 1);
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}
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}
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static inline unsigned int
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read_number_binary (BitCoderState * b, int bits)
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{
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unsigned int x = 0;
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while (bits) {
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bits--;
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x |= bitcoder_read_bit (b) << bits;
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}
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return x;
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}
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static inline void
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golomb_write_number (BitCoderState * b, unsigned int x, int bits)
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{
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unsigned int q, r;
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int i = 0;
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assert (x > 0);
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while ((q = (x - 1) >> bits) > 0) {
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bitcoder_write_bit (b, 1); /* fast temporary adaption, write */
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bits++; /* unary representation of q */
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i++;
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};
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bitcoder_write_bit (b, 0);
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r = x - 1 - (q << bits);
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write_number_binary (b, r, bits, i + 1);
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}
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static inline unsigned int
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golomb_read_number (BitCoderState * b, int bits)
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{
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unsigned int q = 0, r, x;
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while (bitcoder_read_bit (b) != 0) {
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bits++;
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}
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r = read_number_binary (b, bits);
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x = (q << bits) + r + 1;
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return x;
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}
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typedef struct
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{
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uint8_t count;
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uint8_t bits; /* a 5.3 fixed point integer */
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} GolombAdaptiveCoderState;
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#define GOLOMB_ADAPTIVE_CODER_STATE_INITIALIZER { 8<<3, 0 }
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static const int golomb_w_tab[] = { 256, 128, 64 };
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static inline void
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golombcoder_encode_number (GolombAdaptiveCoderState * g,
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BitCoderState * b, unsigned int x)
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{
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golomb_write_number (b, x, g->bits >> 3);
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g->bits = ((256 - golomb_w_tab[g->count]) * (int) g->bits +
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golomb_w_tab[g->count] * (required_bits (x) << 3)) / 256;
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g->count++;
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if (g->count > 2)
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g->count = 2;
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}
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static inline unsigned int
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golombcoder_decode_number (GolombAdaptiveCoderState * g, BitCoderState * b)
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{
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unsigned int x;
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x = golomb_read_number (b, g->bits >> 3);
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g->bits = ((256 - golomb_w_tab[g->count]) * g->bits +
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golomb_w_tab[g->count] * (required_bits (x) << 3)) / 256;
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g->count++;
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if (g->count > 2)
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g->count = 2;
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return x;
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}
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#endif
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