>From 353cc7c6906f650fa228d295dad270637f9441c7 Mon Sep 17 00:00:00 2001
From: Bruno Haible <bruno@clisp.org>
Date: Tue, 4 Aug 2020 00:05:05 +0200
Subject: [PATCH 1/6] ffs: Optimize for MSVC.

* lib/ffs.c: Include <intrin.h>.
(ffs): With MSVC, use the _BitScanForward built-in.
---
 ChangeLog |  6 ++++++
 lib/ffs.c | 12 ++++++++++++
 2 files changed, 18 insertions(+)

diff --git a/ChangeLog b/ChangeLog
index 526747e..773a9f5 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,11 @@
 2020-08-03  Bruno Haible  <bruno@clisp.org>
 
+	ffs: Optimize for MSVC.
+	* lib/ffs.c: Include <intrin.h>.
+	(ffs): With MSVC, use the _BitScanForward built-in.
+
+2020-08-03  Bruno Haible  <bruno@clisp.org>
+
 	sigprocmask: Try to avoid breakage for people who use an Autoconf cache.
 	* m4/signalblocking.m4 (gl_SIGNALBLOCKING): Change the name of the cache
 	variable.
diff --git a/lib/ffs.c b/lib/ffs.c
index ba4915e..d8a65ca 100644
--- a/lib/ffs.c
+++ b/lib/ffs.c
@@ -23,11 +23,23 @@
 
 #include <limits.h>
 
+#if defined _MSC_VER
+# include <intrin.h>
+#endif
+
 int
 ffs (int i)
 {
 #if __GNUC__ > 3 || (__GNUC__ == 3 && __GNUC_MINOR__ >= 4)
   return __builtin_ffs (i);
+#elif defined _MSC_VER
+  /* _BitScanForward
+     <https://docs.microsoft.com/en-us/cpp/intrinsics/bitscanforward-bitscanforward64> */
+  unsigned long bit;
+  if (_BitScanForward (&bit, i))
+    return bit + 1;
+  else
+    return 0;
 #else
   /* <https://github.com/gibsjose/BitHacks>
      gives this deBruijn constant for a branch-less computation, although
-- 
2.7.4