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Speed up cksum word-by-word with a 15 KB table generated dynamically. 

(Really we could generate the main table dynamically too.)

From anonymous.
This commit is contained in:
riastradh 2020-04-27 03:26:09 +00:00
parent 89f8a416b9
commit 6211b6d5e0
1 changed files with 57 additions and 11 deletions
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68
usr.bin/cksum/crc.c
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@ -1,4 +1,4 @@
/* $NetBSD: crc.c,v 1.19 2014/10/29 18:09:35 uebayasi Exp $ */
/* $NetBSD: crc.c,v 1.20 2020/04/27 03:26:09 riastradh Exp $ */
/*-
* Copyright (c) 1991, 1993
@ -41,11 +41,13 @@
#if 0
static char sccsid[] = "@(#)crc.c 8.1 (Berkeley) 6/17/93";
#else
__RCSID("$NetBSD: crc.c,v 1.19 2014/10/29 18:09:35 uebayasi Exp $");
__RCSID("$NetBSD: crc.c,v 1.20 2020/04/27 03:26:09 riastradh Exp $");
#endif
#endif /* not lint */
#include <sys/types.h>
#include <sys/endian.h>
#include <unistd.h>
#include "extern.h"
@ -114,20 +116,17 @@ static const u_int32_t crctab[] = {
int
crc(int fd, u_int32_t *cval, off_t *clen)
{
u_char *p;
ssize_t nr;
u_int32_t thecrc;
off_t len;
u_char buf[16 * 1024];
#define COMPUTE(var, ch) (var) = (var) << 8 ^ crctab[(var) >> 24 ^ (ch)]
thecrc = 0;
len = 0;
while ((nr = read(fd, buf, sizeof(buf))) > 0)
for (len += nr, p = buf; nr--; ++p) {
COMPUTE(thecrc, *p);
}
while ((nr = read(fd, buf, sizeof(buf))) > 0) {
thecrc = crc_buf(thecrc, buf, nr);
len += nr;
}
if (nr < 0)
return 1;
@ -135,13 +134,31 @@ crc(int fd, u_int32_t *cval, off_t *clen)
/* Include the length of the file. */
for (; len != 0; len >>= 8) {
COMPUTE(thecrc, len & 0xff);
thecrc = crc_byte(thecrc, len & 0xff);
}
*cval = ~thecrc;
return 0;
}
#define COMPUTE(var, ch) (var) = (var) << 8 ^ crctab[(var) >> 24 ^ (ch)]
static uint32_t crcslice[15][256];
static void
tables(void)
{
int a, b;
for (a = 0; a < 256; a++) {
uint32_t crc = crctab[a];
for (b = 0; b < 15; b++) {
COMPUTE(crc, 0);
crcslice[b][a] = crc;
}
}
}
/* These two are rather more useful to the outside world */
uint32_t
@ -149,8 +166,37 @@ crc_buf(uint32_t thecrc, const void *buf, size_t len)
{
const uint8_t *p = buf;
for (p = buf; len; p++, len--)
/* Compute the tables once. */
if (crcslice[14][255] == 0)
tables();
for (; len >= 16; p += 16, len -= 16) {
uint32_t a = be32dec(p + 0) ^ thecrc;
uint32_t b = be32dec(p + 4);
uint32_t c = be32dec(p + 8);
uint32_t d = be32dec(p + 12);
thecrc =
crcslice[14][a >> 24 & 0xff] ^
crcslice[13][a >> 16 & 0xff] ^
crcslice[12][a >> 8 & 0xff] ^
crcslice[11][a >> 0 & 0xff] ^
crcslice[10][b >> 24 & 0xff] ^
crcslice[9][b >> 16 & 0xff] ^
crcslice[8][b >> 8 & 0xff] ^
crcslice[7][b >> 0 & 0xff] ^
crcslice[6][c >> 24 & 0xff] ^
crcslice[5][c >> 16 & 0xff] ^
crcslice[4][c >> 8 & 0xff] ^
crcslice[3][c >> 0 & 0xff] ^
crcslice[2][d >> 24 & 0xff] ^
crcslice[1][d >> 16 & 0xff] ^
crcslice[0][d >> 8 & 0xff] ^
crctab[d >> 0 & 0xff];
}
for (; len; p++, len--)
COMPUTE(thecrc, *p);
return thecrc;
}