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author | bde <bde@FreeBSD.org> | 1995-07-11 18:50:47 +0000 |
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committer | bde <bde@FreeBSD.org> | 1995-07-11 18:50:47 +0000 |
commit | 8c00ee9d2cf8b5f40ce099f07118ce1251fd57e0 (patch) | |
tree | 4380167b2d69b7c49777bf14178cbb108f57f443 /sys/libkern | |
parent | e97bb42ff7b5af23eb85cbb418b988c32ae93df6 (diff) | |
download | FreeBSD-src-8c00ee9d2cf8b5f40ce099f07118ce1251fd57e0.zip FreeBSD-src-8c00ee9d2cf8b5f40ce099f07118ce1251fd57e0.tar.gz |
Rearrange the inner loop of scanc() to get better code on i*86's
(on an i486, 10 cycles (+ cache misses) instead of 15). The
change should be a no-op if the compiler is any good. The best
possible i*86 code for the same algorithm is only 1 more cycle
faster on i486's so I don't want to bother implementing an
assembler version.
scanc() is a bottleneck for OPOST processing. It is naturally
about 4 times as slow as bcopy() on 32-bit systems.
Diffstat (limited to 'sys/libkern')
-rw-r--r-- | sys/libkern/scanc.c | 12 |
1 files changed, 10 insertions, 2 deletions
diff --git a/sys/libkern/scanc.c b/sys/libkern/scanc.c index c44a6a6..7bc3fa0 100644 --- a/sys/libkern/scanc.c +++ b/sys/libkern/scanc.c @@ -32,7 +32,7 @@ * * @(#)scanc.c 8.1 (Berkeley) 6/10/93 * - * $Id: scanc.c,v 1.2 1994/08/02 07:44:27 davidg Exp $ + * $Id: scanc.c,v 1.3 1995/03/17 06:15:39 phk Exp $ */ #include <sys/libkern.h> @@ -47,6 +47,14 @@ scanc(size, cp, table, mask0) register u_char mask; mask = mask0; - for (end = &cp[size]; cp < end && (table[*cp] & mask) == 0; ++cp); + for (end = &cp[size]; cp < end; ++cp) { + /* + * gcc-2.6.3 generates poor (un)sign extension code on i386's. + * The cast to volatile should have no effect, but in fact it + * improves the code on i386's. + */ + if (table[*(volatile u_char *)cp] & mask) + break; + } return (end - cp); } |