libavcodec/put_bits.h

/*
 * copyright (c) 2004 Michael Niedermayer <michaelni@gmx.at>
 *
 * 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
 */

/**
 * @file
 * bitstream writer API
 */

#ifndef AVCODEC_PUT_BITS_H
#define AVCODEC_PUT_BITS_H

#include <stdint.h>
#include <stddef.h>

#include "libavutil/intreadwrite.h"
#include "libavutil/avassert.h"

typedef struct PutBitContext {
    uint32_t bit_buf;
    int bit_left;
    uint8_t *buf, *buf_ptr, *buf_end;
    int size_in_bits;
} PutBitContext;

/**
 * Initialize the PutBitContext s.
 *
 * @param buffer the buffer where to put bits
 * @param buffer_size the size in bytes of buffer
 */
static inline void init_put_bits(PutBitContext *s, uint8_t *buffer,
                                 int buffer_size)
{
    if (buffer_size < 0) {
        buffer_size = 0;
        buffer      = NULL;
    }

    s->size_in_bits = 8 * buffer_size;
    s->buf          = buffer;
    s->buf_end      = s->buf + buffer_size;
    s->buf_ptr      = s->buf;
    s->bit_left     = 32;
    s->bit_buf      = 0;
}

/**
 * Rebase the bit writer onto a reallocated buffer.
 *
 * @param buffer the buffer where to put bits
 * @param buffer_size the size in bytes of buffer,
 *                    must be larger than the previous size
 */
static inline void rebase_put_bits(PutBitContext *s, uint8_t *buffer,
                                   int buffer_size)
{
    av_assert0(8*buffer_size > s->size_in_bits);

    s->buf_end = buffer + buffer_size;
    s->buf_ptr = buffer + (s->buf_ptr - s->buf);
    s->buf     = buffer;
    s->size_in_bits = 8 * buffer_size;
}

/**
 * @return the total number of bits written to the bitstream.
 */
static inline int put_bits_count(PutBitContext *s)
{
    return (s->buf_ptr - s->buf) * 8 + 32 - s->bit_left;
}

/**
 * @return the number of bits available in the bitstream.
 */
static inline int put_bits_left(PutBitContext* s)
{
    return (s->buf_end - s->buf_ptr) * 8 - 32 + s->bit_left;
}

/**
 * Pad the end of the output stream with zeros.
 */
static inline void flush_put_bits(PutBitContext *s)
{
#ifndef BITSTREAM_WRITER_LE
    if (s->bit_left < 32)
        s->bit_buf <<= s->bit_left;
#endif
    while (s->bit_left < 32) {
        av_assert0(s->buf_ptr < s->buf_end);
#ifdef BITSTREAM_WRITER_LE
        *s->buf_ptr++ = s->bit_buf;
        s->bit_buf  >>= 8;
#else
        *s->buf_ptr++ = s->bit_buf >> 24;
        s->bit_buf  <<= 8;
#endif
        s->bit_left  += 8;
    }
    s->bit_left = 32;
    s->bit_buf  = 0;
}

#ifdef BITSTREAM_WRITER_LE
#define avpriv_align_put_bits align_put_bits_unsupported_here
#define avpriv_put_string ff_put_string_unsupported_here
#define avpriv_copy_bits avpriv_copy_bits_unsupported_here
#else
/**
 * Pad the bitstream with zeros up to the next byte boundary.
 */
void avpriv_align_put_bits(PutBitContext *s);

/**
 * Put the string string in the bitstream.
 *
 * @param terminate_string 0-terminates the written string if value is 1
 */
void avpriv_put_string(PutBitContext *pb, const char *string,
                       int terminate_string);

/**
 * Copy the content of src to the bitstream.
 *
 * @param length the number of bits of src to copy
 */
void avpriv_copy_bits(PutBitContext *pb, const uint8_t *src, int length);
#endif

/**
 * Write up to 31 bits into a bitstream.
 * Use put_bits32 to write 32 bits.
 */
static inline void put_bits(PutBitContext *s, int n, unsigned int value)
{
    unsigned int bit_buf;
    int bit_left;

    av_assert2(n <= 31 && value < (1U << n));

    bit_buf  = s->bit_buf;
    bit_left = s->bit_left;

    /* XXX: optimize */
#ifdef BITSTREAM_WRITER_LE
    bit_buf |= value << (32 - bit_left);
    if (n >= bit_left) {
        if (3 < s->buf_end - s->buf_ptr) {
            AV_WL32(s->buf_ptr, bit_buf);
            s->buf_ptr += 4;
        } else {
            av_log(NULL, AV_LOG_ERROR, "Internal error, put_bits buffer too small\n");
            av_assert2(0);
        }
        bit_buf     = value >> bit_left;
        bit_left   += 32;
    }
    bit_left -= n;
#else
    if (n < bit_left) {
        bit_buf     = (bit_buf << n) | value;
        bit_left   -= n;
    } else {
        bit_buf   <<= bit_left;
        bit_buf    |= value >> (n - bit_left);
        if (3 < s->buf_end - s->buf_ptr) {
            AV_WB32(s->buf_ptr, bit_buf);
            s->buf_ptr += 4;
        } else {
            av_log(NULL, AV_LOG_ERROR, "Internal error, put_bits buffer too small\n");
            av_assert2(0);
        }
        bit_left   += 32 - n;
        bit_buf     = value;
    }
#endif

    s->bit_buf  = bit_buf;
    s->bit_left = bit_left;
}

static inline void put_sbits(PutBitContext *pb, int n, int32_t value)
{
    av_assert2(n >= 0 && n <= 31);

    put_bits(pb, n, av_mod_uintp2(value, n));
}

/**
 * Write exactly 32 bits into a bitstream.
 */
static void av_unused put_bits32(PutBitContext *s, uint32_t value)
{
    int lo = value & 0xffff;
    int hi = value >> 16;
#ifdef BITSTREAM_WRITER_LE
    put_bits(s, 16, lo);
    put_bits(s, 16, hi);
#else
    put_bits(s, 16, hi);
    put_bits(s, 16, lo);
#endif
}

/**
 * Return the pointer to the byte where the bitstream writer will put
 * the next bit.
 */
static inline uint8_t *put_bits_ptr(PutBitContext *s)
{
    return s->buf_ptr;
}

/**
 * Skip the given number of bytes.
 * PutBitContext must be flushed & aligned to a byte boundary before calling this.
 */
static inline void skip_put_bytes(PutBitContext *s, int n)
{
    av_assert2((put_bits_count(s) & 7) == 0);
    av_assert2(s->bit_left == 32);
    av_assert0(n <= s->buf_end - s->buf_ptr);
    s->buf_ptr += n;
}

/**
 * Skip the given number of bits.
 * Must only be used if the actual values in the bitstream do not matter.
 * If n is 0 the behavior is undefined.
 */
static inline void skip_put_bits(PutBitContext *s, int n)
{
    s->bit_left -= n;
    s->buf_ptr  -= 4 * (s->bit_left >> 5);
    s->bit_left &= 31;
}

/**
 * Change the end of the buffer.
 *
 * @param size the new size in bytes of the buffer where to put bits
 */
static inline void set_put_bits_buffer_size(PutBitContext *s, int size)
{
    av_assert0(size <= INT_MAX/8 - 32);
    s->buf_end = s->buf + size;
    s->size_in_bits = 8*size;
}

#endif /* AVCODEC_PUT_BITS_H */