Provide an optimized implementation of ffs(3) in the kernel on

arm64/powerpc/powerpc64, making use of the count leading zeros
instruction.

powerpc testing by cwen@; ok kettenis@ deraadt@

3 files changed, 47 insertions, 0 deletions

diff --git a/sys/lib/libkern/arch/arm64/ffs.S b/sys/lib/libkern/arch/arm64/ffs.S
new file mode 100644
index 00000000000..03101cb2c9f
--- /dev/null
+++ b/sys/lib/libkern/arch/arm64/ffs.S
@@ -0,0 +1,17 @@
+/*	$OpenBSD: ffs.S,v 1.1 2020/06/10 20:19:29 naddy Exp $ */
+/*
+ * Written by Christian Weisgerber <naddy@openbsd.org>.
+ * Public domain.
+ */
+ 
+#include <machine/asm.h>
+
+ENTRY(ffs)
+	RETGUARD_SETUP(ffs, x15)
+	rbit	w1, w0
+	clz	w1, w1
+	cmp	w0, wzr
+	csinc	w0, wzr, w1, eq
+	RETGUARD_CHECK(ffs, x15)
+	ret
+END(ffs)
diff --git a/sys/lib/libkern/arch/powerpc/ffs.S b/sys/lib/libkern/arch/powerpc/ffs.S
new file mode 100644
index 00000000000..13fe17fb4f8
--- /dev/null
+++ b/sys/lib/libkern/arch/powerpc/ffs.S
@@ -0,0 +1,15 @@
+/*	$OpenBSD: ffs.S,v 1.1 2020/06/10 20:19:29 naddy Exp $ */
+/*
+ * Written by Christian Weisgerber <naddy@openbsd.org>.
+ * Public domain.
+ */
+ 
+#include <machine/asm.h>
+
+ENTRY(ffs)
+	neg	%r4, %r3
+	and	%r3, %r3, %r4
+	cntlzw	%r3, %r3
+	subfic	%r3, %r3, 32
+	blr
+END(ffs)
diff --git a/sys/lib/libkern/arch/powerpc64/ffs.S b/sys/lib/libkern/arch/powerpc64/ffs.S
new file mode 100644
index 00000000000..13fe17fb4f8
--- /dev/null
+++ b/sys/lib/libkern/arch/powerpc64/ffs.S
@@ -0,0 +1,15 @@
+/*	$OpenBSD: ffs.S,v 1.1 2020/06/10 20:19:29 naddy Exp $ */
+/*
+ * Written by Christian Weisgerber <naddy@openbsd.org>.
+ * Public domain.
+ */
+ 
+#include <machine/asm.h>
+
+ENTRY(ffs)
+	neg	%r4, %r3
+	and	%r3, %r3, %r4
+	cntlzw	%r3, %r3
+	subfic	%r3, %r3, 32
+	blr
+END(ffs)