From: Christopher Dykes <cdykes@fb.com>
Date: Mon, 1 Aug 2016 22:26:51 +0000 (-0700)
Subject: Fix the ffs builtins under MSVC
X-Git-Tag: v2016.08.08.00~41
X-Git-Url: http://demsky.eecs.uci.edu/git/?a=commitdiff_plain;h=fcd395244ded1a7adbb5df39ff00d4f9151b762f;p=folly.git

Fix the ffs builtins under MSVC

Summary: I was off by one in my implementation.

Reviewed By: yfeldblum

Differential Revision: D3651183

fbshipit-source-id: 4d6a6d08c06bce332a00088920bf604a10c942e7
---

diff --git a/folly/portability/Builtins.h b/folly/portability/Builtins.h
index 567ca6e9..755e0299 100755
--- a/folly/portability/Builtins.h
+++ b/folly/portability/Builtins.h
@@ -42,14 +42,14 @@ FOLLY_ALWAYS_INLINE int __builtin_ctzll(unsigned long long x) {
 
 FOLLY_ALWAYS_INLINE int __builtin_ffs(int x) {
   unsigned long index;
-  return (int)(_BitScanForward(&index, (unsigned long)x) ? index : 0);
+  return (int)(_BitScanForward(&index, (unsigned long)x) ? index + 1 : 0);
 }
 
 FOLLY_ALWAYS_INLINE int __builtin_ffsl(long x) { return __builtin_ffs((int)x); }
 
 FOLLY_ALWAYS_INLINE int __builtin_ffsll(long long x) {
   unsigned long index;
-  return (int)(_BitScanForward64(&index, (unsigned long long)x) ? index : 0);
+  return (int)(_BitScanForward64(&index, (unsigned long long)x) ? index + 1 : 0);
 }
 
 FOLLY_ALWAYS_INLINE int __builtin_popcountll(unsigned long long x) {