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.

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);
 }