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ffmpeg/libavcodec/bitstream_template.h

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/*
* Copyright (c) 2016 Alexandra Hájková
*
* 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
*/
#ifdef BITSTREAM_TEMPLATE_LE
# define BS_SUFFIX_LOWER _le
# define BS_SUFFIX_UPPER LE
#else
# define BS_SUFFIX_LOWER _be
# define BS_SUFFIX_UPPER BE
#endif
#define BS_JOIN(x, y, z) x ## y ## z
#define BS_JOIN3(x, y, z) BS_JOIN(x, y, z)
#define BS_FUNC(x) BS_JOIN3(bits_, x, BS_SUFFIX_LOWER)
#define BSCTX BS_JOIN3(Bitstream, Context, BS_SUFFIX_UPPER)
typedef struct BSCTX {
uint64_t bits; // stores bits read from the buffer
const uint8_t *buffer, *buffer_end;
const uint8_t *ptr; // pointer to the position inside a buffer
unsigned bits_valid; // number of bits left in bits field
unsigned size_in_bits;
} BSCTX;
/**
* @return
* - 0 on successful refill
* - a negative number when bitstream end is hit
*
* Always succeeds when UNCHECKED_BITSTREAM_READER is enabled.
*/
static inline int BS_FUNC(priv_refill_64)(BSCTX *bc)
{
#if !UNCHECKED_BITSTREAM_READER
if (bc->ptr >= bc->buffer_end)
return -1;
#endif
#ifdef BITSTREAM_TEMPLATE_LE
bc->bits = AV_RL64(bc->ptr);
#else
bc->bits = AV_RB64(bc->ptr);
#endif
bc->ptr += 8;
bc->bits_valid = 64;
return 0;
}
/**
* @return
* - 0 on successful refill
* - a negative number when bitstream end is hit
*
* Always succeeds when UNCHECKED_BITSTREAM_READER is enabled.
*/
static inline int BS_FUNC(priv_refill_32)(BSCTX *bc)
{
#if !UNCHECKED_BITSTREAM_READER
if (bc->ptr >= bc->buffer_end)
return -1;
#endif
#ifdef BITSTREAM_TEMPLATE_LE
bc->bits |= (uint64_t)AV_RL32(bc->ptr) << bc->bits_valid;
#else
bc->bits |= (uint64_t)AV_RB32(bc->ptr) << (32 - bc->bits_valid);
#endif
bc->ptr += 4;
bc->bits_valid += 32;
return 0;
}
/**
* Initialize BitstreamContext.
* @param buffer bitstream buffer, must be AV_INPUT_BUFFER_PADDING_SIZE bytes
* larger than the actual read bits because some optimized bitstream
* readers read 32 or 64 bits at once and could read over the end
* @param bit_size the size of the buffer in bits
* @return 0 on success, AVERROR_INVALIDDATA if the buffer_size would overflow.
*/
static inline int BS_FUNC(init)(BSCTX *bc, const uint8_t *buffer,
unsigned int bit_size)
{
unsigned int buffer_size;
if (bit_size > INT_MAX - 7 || !buffer) {
bc->buffer = NULL;
bc->ptr = NULL;
bc->bits_valid = 0;
return AVERROR_INVALIDDATA;
}
buffer_size = (bit_size + 7) >> 3;
bc->buffer = buffer;
bc->buffer_end = buffer + buffer_size;
bc->ptr = bc->buffer;
bc->size_in_bits = bit_size;
bc->bits_valid = 0;
bc->bits = 0;
BS_FUNC(priv_refill_64)(bc);
return 0;
}
/**
* Initialize BitstreamContext.
* @param buffer bitstream buffer, must be AV_INPUT_BUFFER_PADDING_SIZE bytes
* larger than the actual read bits because some optimized bitstream
* readers read 32 or 64 bits at once and could read over the end
* @param byte_size the size of the buffer in bytes
* @return 0 on success, AVERROR_INVALIDDATA if the buffer_size would overflow
*/
static inline int BS_FUNC(init8)(BSCTX *bc, const uint8_t *buffer,
unsigned int byte_size)
{
if (byte_size > INT_MAX / 8)
return AVERROR_INVALIDDATA;
return BS_FUNC(init)(bc, buffer, byte_size * 8);
}
/**
* Return number of bits already read.
*/
static inline int BS_FUNC(tell)(const BSCTX *bc)
{
return (bc->ptr - bc->buffer) * 8 - bc->bits_valid;
}
/**
* Return buffer size in bits.
*/
static inline int BS_FUNC(size)(const BSCTX *bc)
{
return bc->size_in_bits;
}
/**
* Return the number of the bits left in a buffer.
*/
static inline int BS_FUNC(left)(const BSCTX *bc)
{
return (bc->buffer - bc->ptr) * 8 + bc->size_in_bits + bc->bits_valid;
}
static inline uint64_t BS_FUNC(priv_val_show)(BSCTX *bc, unsigned int n)
{
av_assert2(n > 0 && n <= 64);
#ifdef BITSTREAM_TEMPLATE_LE
return bc->bits & (UINT64_MAX >> (64 - n));
#else
return bc->bits >> (64 - n);
#endif
}
static inline void BS_FUNC(priv_skip_remaining)(BSCTX *bc, unsigned int n)
{
#ifdef BITSTREAM_TEMPLATE_LE
bc->bits >>= n;
#else
bc->bits <<= n;
#endif
bc->bits_valid -= n;
}
static inline uint64_t BS_FUNC(priv_val_get)(BSCTX *bc, unsigned int n)
{
uint64_t ret;
av_assert2(n > 0 && n < 64);
ret = BS_FUNC(priv_val_show)(bc, n);
BS_FUNC(priv_skip_remaining)(bc, n);
return ret;
}
/**
* Return one bit from the buffer.
*/
static inline unsigned int BS_FUNC(read_bit)(BSCTX *bc)
{
if (!bc->bits_valid && BS_FUNC(priv_refill_64)(bc) < 0)
return 0;
return BS_FUNC(priv_val_get)(bc, 1);
}
/**
* Return n bits from the buffer, n has to be in the 1-32 range.
* May be faster than bits_read() when n is not a compile-time constant and is
* known to be non-zero;
*/
static inline uint32_t BS_FUNC(read_nz)(BSCTX *bc, unsigned int n)
{
av_assert2(n > 0 && n <= 32);
if (n > bc->bits_valid) {
if (BS_FUNC(priv_refill_32)(bc) < 0)
bc->bits_valid = n;
}
return BS_FUNC(priv_val_get)(bc, n);
}
/**
* Return n bits from the buffer, n has to be in the 0-32 range.
*/
static inline uint32_t BS_FUNC(read)(BSCTX *bc, unsigned int n)
{
av_assert2(n <= 32);
if (!n)
return 0;
return BS_FUNC(read_nz)(bc, n);
}
/**
* Return n bits from the buffer, n has to be in the 0-63 range.
*/
static inline uint64_t BS_FUNC(read_63)(BSCTX *bc, unsigned int n)
{
uint64_t ret = 0;
unsigned left = 0;
av_assert2(n <= 63);
if (!n)
return 0;
if (n > bc->bits_valid) {
left = bc->bits_valid;
n -= left;
if (left)
ret = BS_FUNC(priv_val_get)(bc, left);
if (BS_FUNC(priv_refill_64)(bc) < 0)
bc->bits_valid = n;
}
#ifdef BITSTREAM_TEMPLATE_LE
ret = BS_FUNC(priv_val_get)(bc, n) << left | ret;
#else
ret = BS_FUNC(priv_val_get)(bc, n) | ret << n;
#endif
return ret;
}
/**
* Return n bits from the buffer, n has to be in the 0-64 range.
*/
static inline uint64_t BS_FUNC(read_64)(BSCTX *bc, unsigned int n)
{
av_assert2(n <= 64);
if (n == 64) {
uint64_t ret = BS_FUNC(read_63)(bc, 63);
#ifdef BITSTREAM_TEMPLATE_LE
return ret | ((uint64_t)BS_FUNC(read_bit)(bc) << 63);
#else
return (ret << 1) | (uint64_t)BS_FUNC(read_bit)(bc);
#endif
}
return BS_FUNC(read_63)(bc, n);
}
/**
* Return n bits from the buffer as a signed integer, n has to be in the 1-32
* range. May be faster than bits_read_signed() when n is not a compile-time
* constant and is known to be non-zero;
*/
static inline int32_t BS_FUNC(read_signed_nz)(BSCTX *bc, unsigned int n)
{
av_assert2(n > 0 && n <= 32);
return sign_extend(BS_FUNC(read_nz)(bc, n), n);
}
/**
* Return n bits from the buffer as a signed integer.
* n has to be in the 0-32 range.
*/
static inline int32_t BS_FUNC(read_signed)(BSCTX *bc, unsigned int n)
{
av_assert2(n <= 32);
if (!n)
return 0;
return BS_FUNC(read_signed_nz)(bc, n);
}
/**
* Return n bits from the buffer but do not change the buffer state.
* n has to be in the 1-32 range. May
*/
static inline uint32_t BS_FUNC(peek_nz)(BSCTX *bc, unsigned int n)
{
av_assert2(n > 0 && n <= 32);
if (n > bc->bits_valid)
BS_FUNC(priv_refill_32)(bc);
return BS_FUNC(priv_val_show)(bc, n);
}
/**
* Return n bits from the buffer but do not change the buffer state.
* n has to be in the 0-32 range.
*/
static inline uint32_t BS_FUNC(peek)(BSCTX *bc, unsigned int n)
{
av_assert2(n <= 32);
if (!n)
return 0;
return BS_FUNC(peek_nz)(bc, n);
}
/**
* Return n bits from the buffer as a signed integer, do not change the buffer
* state. n has to be in the 1-32 range. May be faster than bits_peek_signed()
* when n is not a compile-time constant and is known to be non-zero;
*/
static inline int BS_FUNC(peek_signed_nz)(BSCTX *bc, unsigned int n)
{
av_assert2(n > 0 && n <= 32);
return sign_extend(BS_FUNC(peek_nz)(bc, n), n);
}
/**
* Return n bits from the buffer as a signed integer,
* do not change the buffer state.
* n has to be in the 0-32 range.
*/
static inline int BS_FUNC(peek_signed)(BSCTX *bc, unsigned int n)
{
av_assert2(n <= 32);
if (!n)
return 0;
return BS_FUNC(peek_signed_nz)(bc, n);
}
/**
* Skip n bits in the buffer.
*/
static inline void BS_FUNC(skip)(BSCTX *bc, unsigned int n)
{
if (n < bc->bits_valid)
BS_FUNC(priv_skip_remaining)(bc, n);
else {
n -= bc->bits_valid;
bc->bits = 0;
bc->bits_valid = 0;
if (n >= 64) {
unsigned int skip = n / 8;
n -= skip * 8;
bc->ptr += skip;
}
BS_FUNC(priv_refill_64)(bc);
if (n)
BS_FUNC(priv_skip_remaining)(bc, n);
}
}
/**
* Seek to the given bit position.
*/
static inline void BS_FUNC(seek)(BSCTX *bc, unsigned pos)
{
bc->ptr = bc->buffer;
bc->bits = 0;
bc->bits_valid = 0;
BS_FUNC(skip)(bc, pos);
}
/**
* Skip bits to a byte boundary.
*/
static inline const uint8_t *BS_FUNC(align)(BSCTX *bc)
{
unsigned int n = -BS_FUNC(tell)(bc) & 7;
if (n)
BS_FUNC(skip)(bc, n);
return bc->buffer + (BS_FUNC(tell)(bc) >> 3);
}
/**
* Read MPEG-1 dc-style VLC (sign bit + mantissa with no MSB).
* If MSB not set it is negative.
* @param n length in bits
*/
static inline int BS_FUNC(read_xbits)(BSCTX *bc, unsigned int n)
{
int32_t cache = BS_FUNC(peek)(bc, 32);
int sign = ~cache >> 31;
BS_FUNC(priv_skip_remaining)(bc, n);
return ((((uint32_t)(sign ^ cache)) >> (32 - n)) ^ sign) - sign;
}
/**
* Return decoded truncated unary code for the values 0, 1, 2.
*/
static inline int BS_FUNC(decode012)(BSCTX *bc)
{
if (!BS_FUNC(read_bit)(bc))
return 0;
else
return BS_FUNC(read_bit)(bc) + 1;
}
/**
* Return decoded truncated unary code for the values 2, 1, 0.
*/
static inline int BS_FUNC(decode210)(BSCTX *bc)
{
if (BS_FUNC(read_bit)(bc))
return 0;
else
return 2 - BS_FUNC(read_bit)(bc);
}
/* Read sign bit and flip the sign of the provided value accordingly. */
static inline int BS_FUNC(apply_sign)(BSCTX *bc, int val)
{
int sign = BS_FUNC(read_signed)(bc, 1);
return (val ^ sign) - sign;
}
static inline int BS_FUNC(skip_1stop_8data)(BSCTX *s)
{
if (BS_FUNC(left)(s) <= 0)
return AVERROR_INVALIDDATA;
while (BS_FUNC(read_bit)(s)) {
BS_FUNC(skip)(s, 8);
if (BS_FUNC(left)(s) <= 0)
return AVERROR_INVALIDDATA;
}
return 0;
}
/**
* Return the LUT element for the given bitstream configuration.
*/
static inline int BS_FUNC(priv_set_idx)(BSCTX *bc, int code, int *n,
int *nb_bits, const VLCElem *table)
{
unsigned idx;
*nb_bits = -*n;
idx = BS_FUNC(peek)(bc, *nb_bits) + code;
*n = table[idx].len;
return table[idx].sym;
}
/**
* Parse a vlc code.
* @param bits is the number of bits which will be read at once, must be
* identical to nb_bits in init_vlc()
* @param max_depth is the number of times bits bits must be read to completely
* read the longest vlc code
* = (max_vlc_length + bits - 1) / bits
* If the vlc code is invalid and max_depth=1, then no bits will be removed.
* If the vlc code is invalid and max_depth>1, then the number of bits removed
* is undefined.
*/
static inline int BS_FUNC(read_vlc)(BSCTX *bc, const VLCElem *table,
int bits, int max_depth)
{
int nb_bits;
unsigned idx = BS_FUNC(peek)(bc, bits);
int code = table[idx].sym;
int n = table[idx].len;
if (max_depth > 1 && n < 0) {
BS_FUNC(priv_skip_remaining)(bc, bits);
code = BS_FUNC(priv_set_idx)(bc, code, &n, &nb_bits, table);
if (max_depth > 2 && n < 0) {
BS_FUNC(priv_skip_remaining)(bc, nb_bits);
code = BS_FUNC(priv_set_idx)(bc, code, &n, &nb_bits, table);
}
}
BS_FUNC(priv_skip_remaining)(bc, n);
return code;
}
#undef BSCTX
#undef BS_FUNC
#undef BS_JOIN3
#undef BS_JOIN
#undef BS_SUFFIX_UPPER
#undef BS_SUFFIX_LOWER
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