windows-server-2003/base/mspatch/lzx/decoder/decin.c

/*
 * decin.c
 *
 * Decoder inputting of compressed data
 */
#include "decoder.h"


/*
 * Initialises the bit buffer state
 */
void NEAR initialise_decoder_bitbuf(t_decoder_context *context)
{
    byte *p;

    /*
     * If we're decoding an uncompressed block, don't use the
     * bit buffer; we're reading directly out of the input.
     */
    if (context->dec_block_type == BLOCKTYPE_UNCOMPRESSED)
        return;

    if ((context->dec_input_curpos + sizeof(ulong)) > context->dec_end_input_pos)
        return;

    p = context->dec_input_curpos;

    context->dec_bitbuf =
    ((ulong) p[2] | (((ulong) p[3]) << 8)) |
    ((((ulong) p[0] | (((ulong) p[1]) << 8))) << 16);

    context->dec_bitcount = 16;
    context->dec_input_curpos += 4;
}


/*
 * Initialise input buffer and bitwise i/o
 */
void NEAR init_decoder_input(t_decoder_context *context)
{
    initialise_decoder_bitbuf(context);
}


void NEAR fillbuf(t_decoder_context *context, int n)
{
    context->dec_bitbuf <<= n;
    context->dec_bitcount -= (char)n;

    if (context->dec_bitcount <= 0)
        {
        if (context->dec_input_curpos >= context->dec_end_input_pos)
            {
            context->dec_error_condition = true;
            return;
            }

        context->dec_bitbuf |= ((((ulong) *context->dec_input_curpos | (((ulong) *(context->dec_input_curpos+1)) << 8))) << (-context->dec_bitcount));
        context->dec_input_curpos += 2;
        context->dec_bitcount += 16;

        if (context->dec_bitcount <= 0)
            {
            if (context->dec_input_curpos >= context->dec_end_input_pos)
                {
                context->dec_error_condition = true;
                return;
                }

            context->dec_bitbuf |= ((((ulong) *context->dec_input_curpos | (((ulong) *(context->dec_input_curpos+1)) << 8))) << (-context->dec_bitcount));
            context->dec_input_curpos += 2;
            context->dec_bitcount += 16;
            }
        }
}


ulong NEAR getbits(t_decoder_context *context, int n)
{
    ulong value;

    value = context->dec_bitbuf >> (32-(n));
    fillbuf(context, n);

    return value;
}