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minor optimizations to FLAC__bitreader_read_rice_signed_block()

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This commit is contained in:
Josh Coalson
2007-03-22 03:19:52 +00:00
parent c9212fa01b
commit f1dfaebdfa
1 changed files with 20 additions and 22 deletions
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42
src/libFLAC/bitreader.c
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@@ -817,7 +817,6 @@ FLAC__bool FLAC__bitreader_read_rice_signed_block(FLAC__BitReader *br, int vals[
{ {
unsigned i; unsigned i;
unsigned uval = 0; unsigned uval = 0;
unsigned bits; /* the # of binary LSBs left to read to finish a rice codeword */
/* try and get br->consumed_words and br->consumed_bits into register; /* try and get br->consumed_words and br->consumed_bits into register;
* must remember to flush them back to *br before calling other * must remember to flush them back to *br before calling other
@@ -855,7 +854,6 @@ FLAC__bool FLAC__bitreader_read_rice_signed_block(FLAC__BitReader *br, int vals[
#endif #endif
uval += i; uval += i;
cbits += i; cbits += i;
bits = parameter;
cbits++; /* skip over stop bit */ cbits++; /* skip over stop bit */
if(cbits == FLAC__BITS_PER_WORD) { if(cbits == FLAC__BITS_PER_WORD) {
crc16_update_word_(br, br->buffer[cwords]); crc16_update_word_(br, br->buffer[cwords]);
@@ -891,7 +889,6 @@ FLAC__bool FLAC__bitreader_read_rice_signed_block(FLAC__BitReader *br, int vals[
#endif #endif
uval += i; uval += i;
cbits += i; cbits += i;
bits = parameter;
cbits++; /* skip over stop bit */ cbits++; /* skip over stop bit */
FLAC__ASSERT(cbits < FLAC__BITS_PER_WORD); FLAC__ASSERT(cbits < FLAC__BITS_PER_WORD);
goto break1; goto break1;
@@ -925,8 +922,8 @@ break1:
/* read binary part */ /* read binary part */
FLAC__ASSERT(cwords <= br->words); FLAC__ASSERT(cwords <= br->words);
if(bits) { if(parameter) {
while(ucbits < bits) { while(ucbits < parameter) {
/* flush registers and read; bitreader_read_from_client_() does /* flush registers and read; bitreader_read_from_client_() does
* not touch br->consumed_bits at all but we still need to set * not touch br->consumed_bits at all but we still need to set
* it in case it fails and we have to return false. * it in case it fails and we have to return false.
@@ -943,15 +940,16 @@ break1:
/* this also works when consumed_bits==0, it's just a little slower than necessary for that case */ /* this also works when consumed_bits==0, it's just a little slower than necessary for that case */
const unsigned n = FLAC__BITS_PER_WORD - cbits; const unsigned n = FLAC__BITS_PER_WORD - cbits;
const brword word = br->buffer[cwords]; const brword word = br->buffer[cwords];
if(bits < n) { unsigned bits;
uval <<= bits; if(parameter < n) {
uval |= (word & (FLAC__WORD_ALL_ONES >> cbits)) >> (n-bits); uval <<= parameter;
cbits += bits; uval |= (word & (FLAC__WORD_ALL_ONES >> cbits)) >> (n-parameter);
cbits += parameter;
goto break2; goto break2;
} }
uval <<= n; uval <<= n;
uval |= word & (FLAC__WORD_ALL_ONES >> cbits); uval |= word & (FLAC__WORD_ALL_ONES >> cbits);
bits -= n; bits = parameter - n;
crc16_update_word_(br, word); crc16_update_word_(br, word);
cwords++; cwords++;
cbits = 0; cbits = 0;
@@ -963,29 +961,29 @@ break1:
goto break2; goto break2;
} }
else { else {
FLAC__ASSERT(bits < FLAC__BITS_PER_WORD); FLAC__ASSERT(parameter < FLAC__BITS_PER_WORD);
uval <<= bits; uval <<= parameter;
uval |= br->buffer[cwords] >> (FLAC__BITS_PER_WORD-bits); uval |= br->buffer[cwords] >> (FLAC__BITS_PER_WORD-parameter);
cbits = bits; cbits = parameter;
goto break2; goto break2;
} }
} }
else { else {
/* in this case we're starting our read at a partial tail word; /* in this case we're starting our read at a partial tail word;
* the reader has guaranteed that we have at least 'bits' bits * the reader has guaranteed that we have at least 'parameter'
* available to read, which makes this case simpler. * bits available to read, which makes this case simpler.
*/ */
uval <<= bits; uval <<= parameter;
if(cbits) { if(cbits) {
/* this also works when consumed_bits==0, it's just a little slower than necessary for that case */ /* this also works when consumed_bits==0, it's just a little slower than necessary for that case */
FLAC__ASSERT(cbits + bits <= br->bytes*8); FLAC__ASSERT(cbits + parameter <= br->bytes*8);
uval |= (br->buffer[cwords] & (FLAC__WORD_ALL_ONES >> cbits)) >> (FLAC__BITS_PER_WORD-cbits-bits); uval |= (br->buffer[cwords] & (FLAC__WORD_ALL_ONES >> cbits)) >> (FLAC__BITS_PER_WORD-cbits-parameter);
cbits += bits; cbits += parameter;
goto break2; goto break2;
} }
else { else {
uval |= br->buffer[cwords] >> (FLAC__BITS_PER_WORD-bits); uval |= br->buffer[cwords] >> (FLAC__BITS_PER_WORD-parameter);
cbits += bits; cbits += parameter;
goto break2; goto break2;
} }
} }