windows-xp/Source/XPSP1/NT/enduser/stuff/itss/lzx/decoder/decuncmp.c

/*
 * decuncmp.c
 *
 * Decoding uncompressed blocks
 */
#include "decoder.h"


int decode_uncompressed_block(t_decoder_context *context, long bufpos, int amount_to_decode)
{
	long	bytes_decoded = 0;
	long	bufpos_end;
	long	decode_residue;
    ulong   bufpos_start;
    ulong   end_copy_pos;
    byte *  p;

    bufpos_start = bufpos;
	bufpos_end = bufpos + amount_to_decode;

    p = context->dec_input_curpos;

	while (bufpos < bufpos_end)
	{
        if (p >= context->dec_end_input_pos)
            return -1; // input overflow

        context->dec_mem_window[bufpos++] = *p++;
	}

    context->dec_input_curpos = p;

    /*
     * Make sure the MAX_MATCH bytes starting at window[window_size]
     * are always the same as the first MAX_MATCH bytes starting at
     * window[0].  This is for our optimisation in decverb.c and
     * decalign.c which allows us to not have to & window_mask all the
     * time.
     */
    end_copy_pos = (((MAX_MATCH) < (bufpos_end)) ? (MAX_MATCH) : (bufpos_end));

    /*
     * Keep copying until we hit MAX_MATCH or the number of bytes
     * we decoded
     */
    while (bufpos_start < end_copy_pos)
    {
        context->dec_mem_window[bufpos_start + context->dec_window_size] =
            context->dec_mem_window[bufpos_start];
        bufpos_start++;
    }

	decode_residue = bufpos - bufpos_end;

	bufpos &= context->dec_window_mask;
	context->dec_bufpos = bufpos;

    return (int) decode_residue;
}


bool handle_beginning_of_uncompressed_block(t_decoder_context *context)
{
    int     i;

    /*
     * we want to read the 16 bits already in bitbuf, so backtrack
     * the input pointer by 2 bytes.
     */
    context->dec_input_curpos -= 2;

    if (context->dec_input_curpos+4 >= context->dec_end_input_pos)
        return false;

	/*
	 * update LRU repeated offset list
	 */
    for (i = 0; i < NUM_REPEATED_OFFSETS; i++)
    {
        context->dec_last_matchpos_offset[i] =
            ((ulong) *(  (byte *) context->dec_input_curpos)    )        |
            ((ulong) *( ((byte *) context->dec_input_curpos) + 1) << 8)  |
            ((ulong) *( ((byte *) context->dec_input_curpos) + 2) << 16) |
            ((ulong) *( ((byte *) context->dec_input_curpos) + 3) << 24);

        context->dec_input_curpos += 4; /* increment by 4 bytes */
    }

    return true;
}