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Rearrange the inner loop of scanc() to get better code on i*86's

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(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.
This commit is contained in:
Bruce Evans 1995-07-11 18:50:47 +00:00
parent d800e06858
commit 5182dcbec2
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=9485
1 changed files with 10 additions and 2 deletions
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12
sys/libkern/scanc.c
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@ -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);
}