bs.c

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/* 
 * h264bitstream - a library for reading and writing H.264 video
 * Copyright (C) 2005-2006 Auroras Entertainment, LLC
 * 
 * Written by Alex Izvorski <aizvorski@gmail.com>
 * 
 * This library 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.
 * 
 * This library 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 this library; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
 */

#include <stdint.h>

#include "bs.h"

/****** bitstream operations *******/

void     bs_init(bs_t* b, uint8_t* buf, int size)
{
        b->start = buf;
        b->p = buf;
        b->end = buf + size;
        b->bits_left = 8;
}

uint32_t bs_byte_aligned(bs_t* b) { if (b->bits_left == 8) { return 1; } else { return 0; } }

uint32_t bs_eof(bs_t* b) { if (b->p >= b->end) { return 1; } else { return 0; } }

int bs_pos(bs_t* b) { return (b->p - b->start); }

uint32_t bs_read_u1(bs_t* b)
{
        uint32_t r = 0;
        if (bs_eof(b)) { return 0; }
        
        b->bits_left--;
        r = ((*(b->p)) >> b->bits_left) & 0x01;

        if (b->bits_left == 0) { b->p ++; b->bits_left = 8; }

        return r;
}

uint32_t bs_read_u(bs_t* b, int n)
{
        uint32_t r = 0;
        int i;
        for (i = 0; i < n; i++)
        {
                r |= ( bs_read_u1(b) << ( n - i - 1 ) );
        }
        return r;
}

uint32_t bs_read_f(bs_t* b, int n) { return bs_read_u(b, n); }

uint32_t bs_read_u8(bs_t* b) { return bs_read_u(b, 8); }

uint32_t bs_read_ue(bs_t* b)
{
        int32_t r = 0;
        int i = 0;

    while( bs_read_u1(b) == 0 && i < 32 && !bs_eof(b) )
    {
        i++;
    }
        r = bs_read_u(b, i);
        r += (1 << i) - 1;
        return r;
}

int32_t bs_read_se(bs_t* b) 
{
        int32_t r = bs_read_ue(b);
        if (r & 0x01)
        {
                r = (r+1)/2;
        }
        else
        {
                r = -(r/2);
        }
        return r;
}


void bs_write_u1(bs_t* b, uint32_t v)
{
        if (bs_eof(b)) { return; }
        
        b->bits_left--;
        (*(b->p)) |= ((v & 0x01) << b->bits_left);

        if (b->bits_left == 0) { b->p ++; b->bits_left = 8; }
}

void bs_write_u(bs_t* b, int n, uint32_t v)
{
        int i;
        for (i = 0; i < n; i++)
        {
                bs_write_u1(b, (v >> ( n - i - 1 ))&0x01 );
        }
}

void bs_write_f(bs_t* b, int n, uint32_t v) { bs_write_u(b, n, v); }

void bs_write_u8(bs_t* b, uint32_t v) { bs_write_u(b, 8, v); }

void bs_write_ue(bs_t* b, uint32_t v)
{
    static const int len_table[256] =
    {
        1,
                1,
                2,2,
                3,3,3,3,
                4,4,4,4,4,4,4,4,
                5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,
        6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,
                6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,
        7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,
                7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,
        7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,
                7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,
        8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,
                8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,
        8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,
                8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,
        8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,
                8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,
        8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,
                8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,
    };

    int len;

    if (v == 0)
    {
        bs_write_u1(b, 1);
    }
    else
    {
                v++;

                if (v >= 0x01000000)
                {
                        len = 24 + len_table[ v >> 24 ];
                }
        else if(v >= 0x00010000)
        {
            len = 16 + len_table[ v >> 16 ];
        }
        else if(v >= 0x00000100)
        {
            len =  8 + len_table[ v >>  8 ];
        }
        else 
        {
            len = len_table[ v ];
        }

        bs_write_u(b, 2*len-1, v);
    }
}

void bs_write_se(bs_t* b, int32_t v)
{
        if (v <= 0)
        {
                bs_write_ue(b, -v*2);
        }
        else
        {
                bs_write_ue(b, v*2 - 1);
        }
}

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