299 lines
7.6 KiB
C
299 lines
7.6 KiB
C
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/*
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* decverb.c
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*
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* Decoding verbatim-bit blocks
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*/
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#include "decoder.h"
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static long special_decode_verbatim_block(
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t_decoder_context *context,
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long BufPos,
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int amount_to_decode
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)
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{
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ulong match_pos;
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long bufpos_end;
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int match_length;
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int c;
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ulong dec_bitbuf;
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byte *dec_input_curpos;
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byte *dec_end_input_pos;
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byte *dec_mem_window;
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char dec_bitcount;
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char m;
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/*
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* Store commonly used variables locally
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*/
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dec_bitcount = context->dec_bitcount;
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dec_bitbuf = context->dec_bitbuf;
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dec_input_curpos = context->dec_input_curpos;
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dec_end_input_pos = context->dec_end_input_pos;
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dec_mem_window = context->dec_mem_window;
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bufpos_end = BufPos + amount_to_decode;
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/*
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* We may overflow by up to MAX_MATCH
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*/
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while (BufPos < bufpos_end)
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{
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/* decode an item from the main tree */
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DECODE_MAIN_TREE(c);
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if ((c -= NUM_CHARS) < 0)
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{
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/* it's a character */
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/* note: c - 256 == c if c is a byte */
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context->dec_mem_window[BufPos] = (byte) c;
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/* we know BufPos < bufpos_end here, so no need to check for overflow */
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context->dec_mem_window[context->dec_window_size+BufPos] = (byte) c;
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BufPos++;
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}
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else
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{
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/* get match length header */
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if ((match_length = c & NUM_PRIMARY_LENGTHS) == NUM_PRIMARY_LENGTHS)
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{
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/* get match length footer if necessary */
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DECODE_LEN_TREE_NOEOFCHECK(match_length);
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}
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/* get match position slot */
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m = c >> NL_SHIFT;
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/* read any extra bits for the match position */
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if (m > 2)
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{
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if (m > 3) /* dec_extra_bits[m] != 0 */
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{
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GET_BITS17_NOEOFCHECK(dec_extra_bits[ m ], match_pos);
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match_pos += MP_POS_minus2[m];
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}
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else
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{
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match_pos = 1; // MP_POS_minus2[3];
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}
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/*
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* Add match base to "extra bits". Our match base
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* table has 2 subtracted from all the elements.
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*
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* This is because encoded positions 0,1,2 denote
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* repeated offsets. Encoded position 3 denotes
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* a match 1 character away, 4 encodes 2 away, etc.
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* Hence the subtraction of 2, which has been
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* incorporated into the table.
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*/
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/* update LRU repeated offset list */
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context->dec_last_matchpos_offset[2] = context->dec_last_matchpos_offset[1];
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context->dec_last_matchpos_offset[1] = context->dec_last_matchpos_offset[0];
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context->dec_last_matchpos_offset[0] = match_pos;
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}
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else
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{
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/* positions 0, 1, 2 denote repeated offsets */
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match_pos = context->dec_last_matchpos_offset[m];
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if (m)
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{
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context->dec_last_matchpos_offset[m] = context->dec_last_matchpos_offset[0];
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context->dec_last_matchpos_offset[0] = match_pos;
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}
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}
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/* match lengths range from 2...257 */
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match_length += MIN_MATCH;
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/* copy match data */
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do
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{
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context->dec_mem_window[BufPos] = context->dec_mem_window[(BufPos-match_pos) & context->dec_window_mask];
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/* replicate bytes */
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if (BufPos < MAX_MATCH)
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context->dec_mem_window[context->dec_window_size+BufPos] = context->dec_mem_window[BufPos];
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BufPos++;
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} while (--match_length > 0);
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}
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}
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context->dec_bitcount = dec_bitcount;
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context->dec_bitbuf = dec_bitbuf;
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context->dec_input_curpos = dec_input_curpos;
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return BufPos;
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}
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#ifdef ASM_DECODE_VERBATIM_BLOCK
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long fast_decode_verbatim_block(
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t_decoder_context *context,
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long BufPos,
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int amount_to_decode
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);
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#else /* !ASM_DECODE_VERBATIM_BLOCK */
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long fast_decode_verbatim_block(t_decoder_context *context, long BufPos, int amount_to_decode)
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{
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ulong match_pos;
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ulong match_ptr;
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long bufpos_end;
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long decode_residue;
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int match_length;
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int c;
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ulong dec_bitbuf;
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byte *dec_input_curpos;
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byte *dec_end_input_pos;
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byte *dec_mem_window;
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char dec_bitcount;
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char m;
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/*
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* Store commonly used variables locally
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*/
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dec_bitcount = context->dec_bitcount;
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dec_bitbuf = context->dec_bitbuf;
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dec_input_curpos = context->dec_input_curpos;
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dec_end_input_pos = context->dec_end_input_pos;
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dec_mem_window = context->dec_mem_window;
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bufpos_end = BufPos + amount_to_decode;
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while (BufPos < bufpos_end)
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{
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/* decode an item from the main tree */
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DECODE_MAIN_TREE(c);
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if ((c -= NUM_CHARS) < 0)
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{
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/* it's a character */
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/* note: c - 256 == c if c is a byte */
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context->dec_mem_window[BufPos++] = (byte) c;
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}
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else
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{
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/* get match length header */
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if ((match_length = c & NUM_PRIMARY_LENGTHS) == NUM_PRIMARY_LENGTHS)
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{
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/* get match length footer if necessary */
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DECODE_LEN_TREE_NOEOFCHECK(match_length);
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}
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/* get match position slot */
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m = c >> NL_SHIFT;
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/* read any extra bits for the match position */
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if (m > 2)
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{
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if (m > 3) /* dec_extra_bits[m] != 0 */
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{
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GET_BITS17_NOEOFCHECK(dec_extra_bits[ m ], match_pos);
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match_pos += MP_POS_minus2[m];
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}
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else
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{
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match_pos = MP_POS_minus2[3];
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}
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/*
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* Add match base to "extra bits". Our match base
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* table has 2 subtracted from all the elements.
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*
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* This is because encoded positions 0,1,2 denote
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* repeated offsets. Encoded position 3 denotes
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* a match 1 character away, 4 encodes 2 away, etc.
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* Hence the subtraction of 2, which has been
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* incorporated into the table.
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*/
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/* update LRU repeated offset list */
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context->dec_last_matchpos_offset[2] = context->dec_last_matchpos_offset[1];
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context->dec_last_matchpos_offset[1] = context->dec_last_matchpos_offset[0];
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context->dec_last_matchpos_offset[0] = match_pos;
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}
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else
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{
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/* positions 0, 1, 2 denote repeated offsets */
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match_pos = context->dec_last_matchpos_offset[m];
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if (m)
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{
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context->dec_last_matchpos_offset[m] = context->dec_last_matchpos_offset[0];
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context->dec_last_matchpos_offset[0] = match_pos;
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}
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}
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/* match lengths range from 2...257 */
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match_length += MIN_MATCH;
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match_ptr = (BufPos - match_pos) & context->dec_window_mask;
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/* copy match data */
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do
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{
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context->dec_mem_window[BufPos++] = context->dec_mem_window[match_ptr++];
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} while (--match_length > 0);
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}
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}
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context->dec_bitcount = dec_bitcount;
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context->dec_bitbuf = dec_bitbuf;
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context->dec_input_curpos = dec_input_curpos;
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/* should be zero */
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decode_residue = BufPos - bufpos_end;
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BufPos &= context->dec_window_mask;
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context->dec_bufpos = BufPos;
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return decode_residue;
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}
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#endif /* ASM_DECODE_VERBATIM_BLOCK */
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int decode_verbatim_block(t_decoder_context *context, long BufPos, int amount_to_decode)
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{
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/*
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* Special case code when BufPos is near the beginning of the window;
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* we must properly update our MAX_MATCH wrapper bytes.
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*/
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if (BufPos < MAX_MATCH)
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{
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long new_bufpos;
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long amount_to_slowly_decode;
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amount_to_slowly_decode = (((MAX_MATCH-BufPos) < (amount_to_decode)) ? (MAX_MATCH-BufPos) : (amount_to_decode));
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/*
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* It's ok to end up decoding more than we wanted if we
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* restricted it to decoding only MAX_MATCH; there's
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* no guarantee a match doesn't straddle MAX_MATCH
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*/
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new_bufpos = special_decode_verbatim_block(
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context,
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BufPos,
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amount_to_slowly_decode
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);
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amount_to_decode -= (new_bufpos-BufPos);
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context->dec_bufpos = BufPos = new_bufpos;
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/*
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* Note: if amount_to_decode < 0 then we're in trouble
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*/
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if (amount_to_decode <= 0)
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return amount_to_decode;
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}
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return fast_decode_verbatim_block(context, BufPos, amount_to_decode);
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}
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