svn commit: r347043 - head/sys/vm

[Douglas William Moore]

Author: dougm
Date: Fri May  3 02:55:54 2019
New Revision: 347043
URL: https://svnweb.freebsd.org/changeset/base/347043

Log:
  fls() should find the most significant bit of an int faster than a
  linear search can, so use it to avoid a linear search in isqrt.
  
  Approved by: kib (mentor), markj (mentor)
  Differential Revision: https://reviews.freebsd.org/D20102

Modified:
  head/sys/vm/vm_pageout.c

Modified: head/sys/vm/vm_pageout.c
==============================================================================
--- head/sys/vm/vm_pageout.c	Fri May  3 02:51:33 2019	(r347042)
+++ head/sys/vm/vm_pageout.c	Fri May  3 02:55:54 2019	(r347043)
@@ -928,9 +928,7 @@ isqrt(u_int num)
 {
 	u_int bit, root, tmp;
 
-	bit = 1u << ((NBBY * sizeof(u_int)) - 2);
-	while (bit > num)
-		bit >>= 2;
+	bit = num != 0 ? (1u << ((fls(num) - 1) & ~1)) : 0;
 	root = 0;
 	while (bit != 0) {
 		tmp = root + bit;