[src/trunk]: src/usr.bin/cksum Speed up cksum word-by-word with a 15 KB table...

[riastradh <riastradh%NetBSD.org@localhost>]

details:   https://anonhg.NetBSD.org/src/rev/94d876853745
branches:  trunk
changeset: 971539:94d876853745
user:      riastradh <riastradh%NetBSD.org@localhost>
date:      Mon Apr 27 03:26:09 2020 +0000

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

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

>From anonymous.

diffstat:

 usr.bin/cksum/crc.c |  68 ++++++++++++++++++++++++++++++++++++++++++++--------
 1 files changed, 57 insertions(+), 11 deletions(-)

diffs (121 lines):

diff -r df1813ffa27e -r 94d876853745 usr.bin/cksum/crc.c
--- a/usr.bin/cksum/crc.c       Mon Apr 27 03:15:12 2020 +0000
+++ b/usr.bin/cksum/crc.c       Mon Apr 27 03:26:09 2020 +0000
@@ -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 @@
 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 @@
 
        /* 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 @@
 {
        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;
 }