path: root/libavcodec/bitstream_template.h

/*
 * 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_LE
#   define BS_SUFFIX le
#else
#   define BS_SUFFIX be
#endif

#define BS_JOIN(x, y) x ## _ ## y
#define BS_FUNC2(x, y) BS_JOIN(x, y)
#define BS_FUNC(x) BS_FUNC2(x, BS_SUFFIX)

static inline void BS_FUNC(refill_64)(BitstreamContext *bc)
{
#if !UNCHECKED_BITSTREAM_READER
    if (bc->ptr >= bc->buffer_end)
        return;
#endif

#ifdef BITSTREAM_LE
    bc->bits       = AV_RL64(bc->ptr);
#else
    bc->bits       = AV_RB64(bc->ptr);
#endif
    bc->ptr       += 8;
    bc->bits_left  = 64;
}

static inline void BS_FUNC(refill_32)(BitstreamContext *bc)
{
#if !UNCHECKED_BITSTREAM_READER
    if (bc->ptr >= bc->buffer_end)
        return;
#endif

#ifdef BITSTREAM_LE
    bc->bits       = (uint64_t)AV_RL32(bc->ptr) << bc->bits_left | bc->bits;
#else
    bc->bits       = bc->bits | (uint64_t)AV_RB32(bc->ptr) << (32 - bc->bits_left);
#endif
    bc->ptr       += 4;
    bc->bits_left += 32;
}

/**
 * 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(bitstream_init)(BitstreamContext *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_left = 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_left    = 0;
    bc->bits         = 0;

    BS_FUNC(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(bitstream_init8)(BitstreamContext *bc, const uint8_t *buffer,
                                           unsigned int byte_size)
{
    if (byte_size > INT_MAX / 8)
        return AVERROR_INVALIDDATA;
    return BS_FUNC(bitstream_init)(bc, buffer, byte_size * 8);
}

static inline uint64_t BS_FUNC(get_val)(BitstreamContext *bc, unsigned int n)
{
    uint64_t ret;

#ifdef BITSTREAM_LE
    ret = bc->bits & ((UINT64_C(1) << n) - 1);
    bc->bits >>= n;
#else
    ret = bc->bits >> (64 - n);
    bc->bits <<= n;
#endif
    bc->bits_left -= n;

    return ret;
}

/**
 * Return one bit from the buffer.
 */
static inline unsigned int BS_FUNC(bitstream_read_bit)(BitstreamContext *bc)
{
    if (!bc->bits_left)
        BS_FUNC(refill_64)(bc);

    return BS_FUNC(get_val)(bc, 1);
}

/**
 * Return n bits from the buffer, n has to be in the 0-63 range.
 */
static inline uint64_t BS_FUNC(bitstream_read_63)(BitstreamContext *bc, unsigned int n)
{
    uint64_t ret = 0;
#ifdef BITSTREAM_LE
    uint64_t left = 0;
#endif

    if (!n)
        return 0;

    if (n > bc->bits_left) {
        n -= bc->bits_left;
#ifdef BITSTREAM_LE
        left = bc->bits_left;
#endif
        ret = BS_FUNC(get_val)(bc, bc->bits_left);
        BS_FUNC(refill_64)(bc);
    }

#ifdef BITSTREAM_LE
    ret = get_val_le(bc, n) << left | ret;
#else
    ret = get_val_be(bc, n) | ret << n;
#endif

    return ret;
}

/**
 * Return n bits from the buffer, n has to be in the 0-32  range.
 */
static inline uint32_t BS_FUNC(bitstream_read)(BitstreamContext *bc, unsigned int n)
{
    if (!n)
        return 0;

    if (n > bc->bits_left) {
        BS_FUNC(refill_32)(bc);
        if (bc->bits_left < 32)
            bc->bits_left = n;
    }

    return BS_FUNC(get_val)(bc, 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(bitstream_read_signed)(BitstreamContext *bc, unsigned int n)
{
    return sign_extend(BS_FUNC(bitstream_read)(bc, n), n);
}

static inline unsigned int BS_FUNC(show_val)(BitstreamContext *bc, unsigned int n)
{
#ifdef BITSTREAM_LE
    return bc->bits & ((UINT64_C(1) << n) - 1);
#else
    return bc->bits >> (64 - n);
#endif
}

/**
 * Return n bits from the buffer but do not change the buffer state.
 * n has to be in the 0-32 range.
 */
static inline unsigned int BS_FUNC(bitstream_peek)(BitstreamContext *bc, unsigned int n)
{
    if (n > bc->bits_left)
        BS_FUNC(refill_32)(bc);

    return BS_FUNC(show_val)(bc, 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(bitstream_peek_signed)(BitstreamContext *bc, unsigned int n)
{
    return sign_extend(BS_FUNC(bitstream_peek)(bc, n), n);
}

/**
 * Skip n bits from the cache. This may only be called if at least n bits are
 * guaranteed to be in the cache, e.g. right after bitstream_peek(n).
 * Otherwise use bitstream_skip().
 */
static inline void BS_FUNC(bitstream_skip_cache)(BitstreamContext *bc, unsigned int n)
{
#ifdef BITSTREAM_LE
    bc->bits >>= n;
#else
    bc->bits <<= n;
#endif
    bc->bits_left -= n;
}

/**
 * Skip n bits in the buffer.
 */
static inline void BS_FUNC(bitstream_skip)(BitstreamContext *bc, unsigned int n)
{
    if (n < bc->bits_left)
        BS_FUNC(bitstream_skip_cache)(bc, n);
    else {
        n -= bc->bits_left;
        bc->bits      = 0;
        bc->bits_left = 0;

        if (n >= 64) {
            unsigned int skip = n / 8;

            n -= skip * 8;
            bc->ptr += skip;
        }
        BS_FUNC(refill_64)(bc);
        if (n)
            BS_FUNC(bitstream_skip_cache)(bc, n);
    }
}

/**
 * Seek to the given bit position.
 */
static inline void BS_FUNC(bitstream_seek)(BitstreamContext *bc, unsigned pos)
{
    bc->ptr       = bc->buffer;
    bc->bits      = 0;
    bc->bits_left = 0;

    BS_FUNC(bitstream_skip)(bc, pos);
}

/**
 * Skip bits to a byte boundary.
 */
static inline const uint8_t *BS_FUNC(bitstream_align)(BitstreamContext *bc)
{
    unsigned int n = -bitstream_tell(bc) & 7;
    if (n)
        BS_FUNC(bitstream_skip)(bc, n);
    return bc->buffer + (bitstream_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(bitstream_read_xbits)(BitstreamContext *bc, unsigned int n)
{
    int32_t cache = BS_FUNC(bitstream_peek)(bc, 32);
    int sign = ~cache >> 31;
    BS_FUNC(bitstream_skip_cache)(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(bitstream_decode012)(BitstreamContext *bc)
{
    if (!BS_FUNC(bitstream_read_bit)(bc))
        return 0;
    else
        return BS_FUNC(bitstream_read_bit)(bc) + 1;
}

/**
 * Return decoded truncated unary code for the values 2, 1, 0.
 */
static inline int BS_FUNC(bitstream_decode210)(BitstreamContext *bc)
{
    if (BS_FUNC(bitstream_read_bit)(bc))
        return 0;
    else
        return 2 - BS_FUNC(bitstream_read_bit)(bc);
}

/* Read sign bit and flip the sign of the provided value accordingly. */
static inline int BS_FUNC(bitstream_apply_sign)(BitstreamContext *bc, int val)
{
    int sign = BS_FUNC(bitstream_read_signed)(bc, 1);
    return (val ^ sign) - sign;
}

static inline int BS_FUNC(bitstream_skip_1stop_8data)(BitstreamContext *s)
{
    if (bitstream_bits_left(s) <= 0)
        return AVERROR_INVALIDDATA;

    while (BS_FUNC(bitstream_read)(s, 1)) {
        BS_FUNC(bitstream_skip)(s, 8);
        if (bitstream_bits_left(s) <= 0)
            return AVERROR_INVALIDDATA;
    }

    return 0;
}

/**
 * Return the LUT element for the given bitstream configuration.
 */
static inline int BS_FUNC(set_idx)(BitstreamContext *bc, int code, int *n, int *nb_bits,
                                   VLC_TYPE (*table)[2])
{
    unsigned idx;

    *nb_bits = -*n;
    idx = BS_FUNC(bitstream_peek)(bc, *nb_bits) + code;
    *n = table[idx][1];

    return table[idx][0];
}

/**
 * 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(bitstream_read_vlc)(BitstreamContext *bc, VLC_TYPE (*table)[2],
                                              int bits, int max_depth)
{
    int nb_bits;
    unsigned idx = BS_FUNC(bitstream_peek)(bc, bits);
    int code     = table[idx][0];
    int n        = table[idx][1];

    if (max_depth > 1 && n < 0) {
        BS_FUNC(bitstream_skip_cache)(bc, bits);
        code = BS_FUNC(set_idx)(bc, code, &n, &nb_bits, table);
        if (max_depth > 2 && n < 0) {
            BS_FUNC(bitstream_skip_cache)(bc, nb_bits);
            code = BS_FUNC(set_idx)(bc, code, &n, &nb_bits, table);
        }
    }
    BS_FUNC(bitstream_skip_cache)(bc, n);

    return code;
}

#undef BS_FUNC
#undef BS_FUNC2
#undef BS_JOIN
#undef BS_SUFFIX