Provide an optimized implementation of ffs(3) in libc on

aarch64/powerpc/powerpc64, making use of the count leading
zeros instruction.  Also add a brief regression test.
ok deraadt@ kettenis@

3 files changed, 26 insertions, 2 deletions

diff --git a/src/regress/lib/libc/Makefile b/src/regress/lib/libc/Makefile
index 3d0712f951..9ad3120961 100644
--- a/src/regress/lib/libc/Makefile
+++ b/src/regress/lib/libc/Makefile
@@ -1,4 +1,4 @@
-#       $OpenBSD: Makefile,v 1.55 2020/03/23 03:01:21 schwarze Exp $
+#       $OpenBSD: Makefile,v 1.56 2020/06/26 20:16:21 naddy Exp $
 
 SUBDIR+= _setjmp
 SUBDIR+= alloca arc4random-fork atexit
@@ -6,7 +6,7 @@ SUBDIR+= basename
 SUBDIR+= cephes cxa-atexit
 SUBDIR+= db dirname
 SUBDIR+= env explicit_bzero
-SUBDIR+= fmemopen fnmatch fpclassify fread
+SUBDIR+= ffs fmemopen fnmatch fpclassify fread
 SUBDIR+= gcvt getaddrinfo getcap getopt getopt_long glob
 SUBDIR+= hsearch
 SUBDIR+= ieeefp ifnameindex
diff --git a/src/regress/lib/libc/ffs/Makefile b/src/regress/lib/libc/ffs/Makefile
new file mode 100644
index 0000000000..1ad004394f
--- /dev/null
+++ b/src/regress/lib/libc/ffs/Makefile
@@ -0,0 +1,6 @@
+PROG=           ffs_test
+
+# prevent constant folding and inlining of __builtin_ffs()
+CFLAGS+=        -ffreestanding
+
+.include <bsd.regress.mk>
diff --git a/src/regress/lib/libc/ffs/ffs_test.c b/src/regress/lib/libc/ffs/ffs_test.c
new file mode 100644
index 0000000000..bc1e5c53c2
--- /dev/null
+++ b/src/regress/lib/libc/ffs/ffs_test.c
@@ -0,0 +1,18 @@
+/*      $OpenBSD: ffs_test.c,v 1.1 2020/06/26 20:16:22 naddy Exp $ */
+/*
+ * Written by Christian Weisgerber <naddy@openbsd.org>.
+ * Public domain.
+ */
+
+#include <assert.h>
+#include <stdint.h>
+#include <string.h>
+
+int
+main(void)
+{
+        assert(ffs(0) == 0);
+        assert(ffs(0x8080) == 8);
+        assert(ffs(INT32_MIN) == 32);
+        return (0);
+}