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deflate_constants: define constant for first len sym

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This commit is contained in:
Eric Biggers 2021-12-31 16:04:49 -06:00
parent 0b6127da2d
commit dd42d1a001
2 changed files with 12 additions and 7 deletions
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18
lib/deflate_compress.c
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@ -1544,7 +1544,7 @@ deflate_write_sequences(struct deflate_output_bitstream * restrict os,
in_next += length;
length_slot = seq->length_slot;
litlen_symbol = 257 + length_slot;
litlen_symbol = DEFLATE_FIRST_LEN_SYM + length_slot;
/* Litlen symbol */
deflate_add_bits(os, codes->codewords.litlen[litlen_symbol],
@ -1615,7 +1615,7 @@ deflate_write_item_list(struct deflate_output_bitstream *os,
} else {
/* Match length */
length_slot = deflate_length_slot[length];
litlen_symbol = 257 + length_slot;
litlen_symbol = DEFLATE_FIRST_LEN_SYM + length_slot;
deflate_add_bits(os, codes->codewords.litlen[litlen_symbol],
codes->lens.litlen[litlen_symbol]);
@ -1747,8 +1747,11 @@ deflate_flush_block(struct libdeflate_compressor * restrict c,
static_cost += 7;
/* Account for the cost of encoding lengths. */
for (sym = 257; sym < 257 + ARRAY_LEN(deflate_extra_length_bits); sym++) {
u32 extra = deflate_extra_length_bits[sym - 257];
for (sym = DEFLATE_FIRST_LEN_SYM;
sym < DEFLATE_FIRST_LEN_SYM + ARRAY_LEN(deflate_extra_length_bits);
sym++) {
u32 extra = deflate_extra_length_bits[
sym - DEFLATE_FIRST_LEN_SYM];
dynamic_cost += c->freqs.litlen[sym] *
(extra + c->codes.lens.litlen[sym]);
static_cost += c->freqs.litlen[sym] *
@ -1825,7 +1828,7 @@ deflate_choose_match(struct libdeflate_compressor *c,
unsigned length_slot = deflate_length_slot[length];
unsigned offset_slot = deflate_get_offset_slot(c, offset);
c->freqs.litlen[257 + length_slot]++;
c->freqs.litlen[DEFLATE_FIRST_LEN_SYM + length_slot]++;
c->freqs.offset[offset_slot]++;
seq->litrunlen_and_length = ((u32)length << 23) | *litrunlen_p;
@ -2319,7 +2322,8 @@ deflate_tally_item_list(struct libdeflate_compressor *c, u32 block_length)
c->freqs.litlen[offset]++;
} else {
/* Match */
c->freqs.litlen[257 + deflate_length_slot[length]]++;
c->freqs.litlen[DEFLATE_FIRST_LEN_SYM +
deflate_length_slot[length]]++;
c->freqs.offset[deflate_get_offset_slot(c, offset)]++;
}
cur_node += length;
@ -2342,7 +2346,7 @@ deflate_set_costs_from_codes(struct libdeflate_compressor *c,
/* Lengths */
for (i = DEFLATE_MIN_MATCH_LEN; i <= DEFLATE_MAX_MATCH_LEN; i++) {
unsigned length_slot = deflate_length_slot[i];
unsigned litlen_sym = 257 + length_slot;
unsigned litlen_sym = DEFLATE_FIRST_LEN_SYM + length_slot;
u32 bits = (lens->litlen[litlen_sym] ? lens->litlen[litlen_sym] : LENGTH_NOSTAT_BITS);
bits += deflate_extra_length_bits[length_slot];
c->p.n.costs.length[i] = bits * BIT_COST;

1
lib/deflate_constants.h
View File

@ -30,6 +30,7 @@
/* Division of symbols in the literal/length code */
#define DEFLATE_NUM_LITERALS 256
#define DEFLATE_END_OF_BLOCK 256
#define DEFLATE_FIRST_LEN_SYM 257
/* Maximum codeword length, in bits, within each Huffman code */
#define DEFLATE_MAX_PRE_CODEWORD_LEN 7