new version of ffs from drahn@

combines binary search and table lookup.
tested on i386, sparc, ppc, hppa

src/lib/libc/string/ffs.c

@@ -1,41 +1,15 @@
-/*-
- * Copyright (c) 1990 The Regents of the University of California.
- * All rights reserved.
- *
- * Redistribution and use in source and binary forms, with or without
- * modification, are permitted provided that the following conditions
- * are met:
- * 1. Redistributions of source code must retain the above copyright
- *    notice, this list of conditions and the following disclaimer.
- * 2. Redistributions in binary form must reproduce the above copyright
- *    notice, this list of conditions and the following disclaimer in the
- *    documentation and/or other materials provided with the distribution.
- * 3. All advertising materials mentioning features or use of this software
- *    must display the following acknowledgement:
- *	This product includes software developed by the University of
- *	California, Berkeley and its contributors.
- * 4. Neither the name of the University nor the names of its contributors
- *    may be used to endorse or promote products derived from this software
- *    without specific prior written permission.
- *
- * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
- * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
- * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
- * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
- * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
- * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
- * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
- * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
- * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
- * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
- * SUCH DAMAGE.
+/*	$OpenBSD: ffs.c,v 1.4 2000/07/02 01:00:01 mickey Exp $	*/
+
+/*
+ * Public domain.
+ * Written by Dale Rahn.
  */
 
 #if defined(LIBC_SCCS) && !defined(lint)
-static char *rcsid = "$OpenBSD: ffs.c,v 1.3 1996/08/19 08:34:01 tholo Exp $";
+static char *rcsid = "$OpenBSD: ffs.c,v 1.4 2000/07/02 01:00:01 mickey Exp $";
 #endif /* LIBC_SCCS and not lint */
 
-#ifndef _KERNEL
+#if !defined(_KERNEL) && !defined(_STANDALONE)
 #include <string.h>
 #else
 #include <lib/libkern/libkern.h>
@@ -49,10 +23,26 @@ ffs(mask)
 	register int mask;
 {
 	register int bit;
+	register unsigned int r = mask;
+	static const signed char t[16] = {
+		-28, 1, 2, 1,
+		  3, 1, 2, 1,
+		  4, 1, 2, 1,
+		  3, 1, 2, 1 };
+
+	bit = 0;
+	if (0 == (r & 0xffff)) {
+		bit += 16;
+		r >>= 16;
+	}
+	if (0 == (r & 0xff)) {
+		bit += 8;
+		r >>= 8;
+	}
+	if (0 == (r & 0xf)) {
+		bit += 4;
+		r >>= 4;
+	}
 
-	if (mask == 0)
-		return(0);
-	for (bit = 1; !(mask & 1); bit++)
-		mask >>= 1;
-	return(bit);
+	return (bit + t[ r & 0xf ]);
 }