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gzip: speed up send_bits()

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Replace one RMW op with store. This speeds up gzip of a png file by ~2%.

function                                             old     new   delta
send_bits                                             62      66      +4

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
This commit is contained in:
Denys Vlasenko 2018-01-31 00:01:06 +01:00
parent d7500f856d
commit b7dfbbcdaa
1 changed files with 6 additions and 6 deletions
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12
archival/gzip.c
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@ -523,7 +523,6 @@ static unsigned file_read(void *buf, unsigned size)
static void send_bits(unsigned value, unsigned length) static void send_bits(unsigned value, unsigned length)
{ {
unsigned new_buf; unsigned new_buf;
unsigned remain;
#ifdef DEBUG #ifdef DEBUG
Tracev((stderr, " l %2d v %4x ", length, value)); Tracev((stderr, " l %2d v %4x ", length, value));
@ -534,25 +533,26 @@ static void send_bits(unsigned value, unsigned length)
new_buf = G1.bi_buf | (value << G1.bi_valid); new_buf = G1.bi_buf | (value << G1.bi_valid);
/* NB: the above may sometimes do "<< 32" shift (undefined) /* NB: the above may sometimes do "<< 32" shift (undefined)
* if check below is changed to "length > remain" instead of >= */ * if check below is changed to "length > BUF_SIZE" instead of >= */
remain = BUF_SIZE - G1.bi_valid; length += G1.bi_valid;
/* If bi_buf is full */ /* If bi_buf is full */
if (length >= remain) { if (length >= BUF_SIZE) {
/* ...use (valid) bits from bi_buf and /* ...use (valid) bits from bi_buf and
* (BUF_SIZE - bi_valid) bits from value, * (BUF_SIZE - bi_valid) bits from value,
* leaving (width - (BUF_SIZE-bi_valid)) unused bits in value. * leaving (width - (BUF_SIZE-bi_valid)) unused bits in value.
*/ */
value >>= (BUF_SIZE - G1.bi_valid);
if (BUF_SIZE == 32) { if (BUF_SIZE == 32) {
put_32bit(new_buf); /* maybe unroll to 2*put_16bit()? */ put_32bit(new_buf); /* maybe unroll to 2*put_16bit()? */
} else { /* 16 */ } else { /* 16 */
put_16bit(new_buf); put_16bit(new_buf);
} }
new_buf = value >> remain; new_buf = value;
length -= BUF_SIZE; length -= BUF_SIZE;
} }
G1.bi_buf = new_buf; G1.bi_buf = new_buf;
G1.bi_valid += length; G1.bi_valid = length;
} }