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gzip: use wider (32-bit, not 16) bi_buf

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function                                             old     new   delta
bi_windup                                             76      74      -2
send_bits                                             70      62      -8

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
This commit is contained in:
Denys Vlasenko 2018-01-30 23:47:45 +01:00
parent e4c4e6ddc3
commit 6ba6a6f28e
1 changed files with 22 additions and 11 deletions
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33
archival/gzip.c
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@ -355,7 +355,7 @@ struct globals {
/* Output buffer. bits are inserted starting at the bottom (least significant
* bits).
*/
unsigned short bi_buf;
unsigned bi_buf; /* was unsigned short */
#undef BUF_SIZE
#define BUF_SIZE (int)(8 * sizeof(G1.bi_buf))
@ -530,17 +530,25 @@ static void send_bits(int value, int length)
Assert(length > 0 && length <= 15, "invalid length");
G1.bits_sent += length;
#endif
BUILD_BUG_ON(BUF_SIZE != 32 && BUF_SIZE != 16);
new_buf = G1.bi_buf | (value << G1.bi_valid);
/* NB: the above may sometimes do "<< 32" shift (undefined)
* if check below is changed to "length > remain" instead of >= */
remain = BUF_SIZE - G1.bi_valid;
/* If not enough room in bi_buf */
if (length > remain) {
/* If bi_buf is full */
if (length >= remain) {
/* ...use (valid) bits from bi_buf and
* (16 - bi_valid) bits from value,
* leaving (width - (16-bi_valid)) unused bits in value.
* (BUF_SIZE - bi_valid) bits from value,
* leaving (width - (BUF_SIZE-bi_valid)) unused bits in value.
*/
put_16bit(new_buf);
new_buf = (ush) value >> remain;
if (BUF_SIZE == 32) {
put_32bit(new_buf); /* maybe unroll to 2*put_16bit()? */
} else { /* 16 */
put_16bit(new_buf);
}
new_buf = (unsigned) value >> remain;
length -= BUF_SIZE;
}
G1.bi_buf = new_buf;
@ -571,10 +579,13 @@ static unsigned bi_reverse(unsigned code, int len)
*/
static void bi_windup(void)
{
if (G1.bi_valid > 8) {
put_16bit(G1.bi_buf);
} else if (G1.bi_valid > 0) {
put_8bit(G1.bi_buf);
unsigned bits = G1.bi_buf;
int cnt = G1.bi_valid;
while (cnt > 0) {
put_8bit(bits);
bits >>= 8;
cnt -= 8;
}
G1.bi_buf = 0;
G1.bi_valid = 0;