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/*
* Extracted 2009 from mplayer 2009-02-10 libavcodec/bitstream.h.
*
* copyright (c) 2004 Michael Niedermayer <michaelni@gmx.at>
*
* Licensed under the GNU Lesser General Public License, see file COPYING.LIB.
*/
/** \file bitstream.h Bitstream structures and inline functions. */
/** Structure for bistream I/O. */
struct getbit_context {
/** Start of the internal buffer. */
const uint8_t *buffer;
/** Length of buffer in bits (always a multiple of 8). */
uint32_t num_bits;
/** Bit counter. */
int index;
};
/** A variable length code table. */
struct vlc {
/** Number of bits of the table. */
int bits;
/** The code and the bits table. */
int16_t (*table)[2];
/** The size of the table. */
int table_size;
/** Amount of memory allocated so far. */
int table_allocated;
};
static inline uint32_t show_bits(struct getbit_context *gbc, int num)
{
int idx = gbc->index;
const char *p;
uint32_t x;
assert(idx + num <= gbc->num_bits);
p = (const char *)gbc->buffer + (idx >> 3);
x = read_u32_be(p);
return (x << (idx & 7)) >> (32 - num);
}
static inline int get_bits_count(struct getbit_context *gbc)
{
return gbc->index;
}
static inline void skip_bits(struct getbit_context *gbc, int n)
{
assert(gbc->index + n <= gbc->num_bits);
gbc->index += n;
}
static inline unsigned int get_bits(struct getbit_context *gbc, int n)
{
unsigned int ret = show_bits(gbc, n); /* checks n */
skip_bits(gbc, n);
return ret;
}
/* This is rather hot, we can do better than get_bits(gbc, 1). */
static inline unsigned int get_bit(struct getbit_context *gbc)
{
int idx;
uint8_t tmp, mask;
assert(gbc->index < gbc->num_bits);
idx = gbc->index++;
tmp = gbc->buffer[idx >> 3];
mask = 1 << (7 - (idx & 7));
return !!(tmp & mask);
}
/**
* Initialize a getbit_context structure.
*
* \param gbc The structure to initialize.
* \param buffer The bitstream buffer.
* \param size The size of the buffer in bytes.
*
* The bitstream buffer must be 4 bytes larger then the actual read bits
* because the bitstream reader might read 32 bits at once and could read over
* the end.
*/
static inline void init_get_bits(struct getbit_context *gbc,
const uint8_t *buffer, int size)
{
gbc->buffer = buffer;
gbc->num_bits = size * 8;
gbc->index = 0;
}
void init_vlc(struct vlc *vlc, int nb_bits, int nb_codes, const void *bits,
const void *codes, int codes_size);
void free_vlc(struct vlc *vlc);
int get_vlc(struct getbit_context *gbc, const struct vlc *vlc);
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