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compress: initialize static codes only when first used

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This commit is contained in:
Eric Biggers 2016-01-30 22:12:46 -06:00
parent d467d99740
commit 569f738807
1 changed files with 38 additions and 36 deletions
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74
src/deflate_compress.c
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@ -304,7 +304,7 @@ struct deflate_compressor {
/* Dynamic Huffman codes for the current block */
struct deflate_codes codes;
/* Static Huffman codes set at allocation time */
/* Static Huffman codes set just before first use */
struct deflate_codes static_codes;
/* A table for fast lookups of offset slot by match offset.
@ -1116,6 +1116,27 @@ deflate_make_huffman_codes(const struct deflate_freqs *freqs,
codes->codewords.offset);
}
/* Initialize c->static_codes. */
static void
deflate_init_static_codes(struct deflate_compressor *c)
{
unsigned i;
for (i = 0; i < 144; i++)
c->freqs.litlen[i] = 1 << (9 - 8);
for (; i < 256; i++)
c->freqs.litlen[i] = 1 << (9 - 9);
for (; i < 280; i++)
c->freqs.litlen[i] = 1 << (9 - 7);
for (; i < 288; i++)
c->freqs.litlen[i] = 1 << (9 - 8);
for (i = 0; i < 32; i++)
c->freqs.offset[i] = 1 << (5 - 5);
deflate_make_huffman_codes(&c->freqs, &c->static_codes);
}
/* Write the header fields common to all DEFLATE block types. */
static void
deflate_write_block_header(struct deflate_output_bitstream *os,
@ -1476,19 +1497,21 @@ deflate_write_block(struct deflate_compressor * restrict c,
/* Account for end-of-block symbol */
c->freqs.litlen[DEFLATE_END_OF_BLOCK]++;
if (items_remaining < MAX_ITEMS_PER_BLOCK - 100) {
/* Use custom ("dynamic") Huffman codes. */
deflate_write_block_header(os, is_final_block,
DEFLATE_BLOCKTYPE_DYNAMIC_HUFFMAN);
deflate_make_huffman_codes(&c->freqs, &c->codes);
deflate_write_huffman_codes(c, os);
codes = &c->codes;
} else {
/* This is a very short block. Just use the static codes. */
deflate_write_block_header(os, is_final_block,
DEFLATE_BLOCKTYPE_STATIC_HUFFMAN);
codes = &c->static_codes;
}
if (items_remaining < MAX_ITEMS_PER_BLOCK - 100) {
/* Use custom ("dynamic") Huffman codes. */
deflate_write_block_header(os, is_final_block,
DEFLATE_BLOCKTYPE_DYNAMIC_HUFFMAN);
deflate_make_huffman_codes(&c->freqs, &c->codes);
deflate_write_huffman_codes(c, os);
codes = &c->codes;
} else {
/* This is a very short block. Just use the static codes. */
deflate_write_block_header(os, is_final_block,
DEFLATE_BLOCKTYPE_STATIC_HUFFMAN);
codes = &c->static_codes;
if (codes->codewords.litlen[0] == 0xFFFFFFFF)
deflate_init_static_codes(c);
}
deflate_write_sequences(os, block_begin, c->sequences, codes);
deflate_write_end_of_block(os, codes);
@ -2377,27 +2400,6 @@ deflate_init_offset_slot_fast(struct deflate_compressor *c)
}
}
/* Initialize c->static_codes. */
static void
deflate_init_static_codes(struct deflate_compressor *c)
{
unsigned i;
for (i = 0; i < 144; i++)
c->freqs.litlen[i] = 1 << (9 - 8);
for (; i < 256; i++)
c->freqs.litlen[i] = 1 << (9 - 9);
for (; i < 280; i++)
c->freqs.litlen[i] = 1 << (9 - 7);
for (; i < 288; i++)
c->freqs.litlen[i] = 1 << (9 - 8);
for (i = 0; i < 32; i++)
c->freqs.offset[i] = 1 << (5 - 5);
deflate_make_huffman_codes(&c->freqs, &c->static_codes);
}
LIBEXPORT struct deflate_compressor *
deflate_alloc_compressor(unsigned int compression_level)
{
@ -2502,7 +2504,7 @@ deflate_alloc_compressor(unsigned int compression_level)
}
deflate_init_offset_slot_fast(c);
deflate_init_static_codes(c);
c->static_codes.codewords.litlen[0] = 0xFFFFFFFF;
return c;
}