From: Orvid King <blah38621@gmail.com>
Date: Mon, 14 Sep 2015 17:53:41 +0000 (-0700)
Subject: MSVC 2015 constexpr in Bits.h
X-Git-Tag: deprecate-dynamic-initializer~409
X-Git-Url: http://demsky.eecs.uci.edu/git/?a=commitdiff_plain;h=72f394052266ab7874cd624b94d548fb68d9323d;p=folly.git

MSVC 2015 constexpr in Bits.h

Summary: MSVC 2015 supports constexpr intrinsics, and, as the GCC builtins are implemented by #287, we can remove all the MSVC specific intrinsic stuff that isn't constexpr supported.
Closes https://github.com/facebook/folly/pull/288

Reviewed By: @yfeldblum

Differential Revision: D2419064

Pulled By: @JoelMarcey
---

diff --git a/folly/Bits.h b/folly/Bits.h
index 4c1182a6..b6d0a23e 100644
--- a/folly/Bits.h
+++ b/folly/Bits.h
@@ -55,10 +55,11 @@
 #ifndef FOLLY_BITS_H_
 #define FOLLY_BITS_H_
 
-#if !defined(__clang__) && !defined(_MSC_VER)
+#if !defined(__clang__) && !(defined(_MSC_VER) && (_MSC_VER < 1900))
 #define FOLLY_INTRINSIC_CONSTEXPR constexpr
 #else
-// GCC is the only compiler with intrinsics constexpr.
+// GCC and MSVC 2015+ are the only compilers with
+// intrinsics constexpr.
 #define FOLLY_INTRINSIC_CONSTEXPR const
 #endif
 
@@ -72,14 +73,6 @@
 # include <byteswap.h>
 #endif
 
-#ifdef _MSC_VER
-# include <intrin.h>
-# pragma intrinsic(_BitScanForward)
-# pragma intrinsic(_BitScanForward64)
-# pragma intrinsic(_BitScanReverse)
-# pragma intrinsic(_BitScanReverse64)
-#endif
-
 #include <cassert>
 #include <cinttypes>
 #include <iterator>
@@ -100,12 +93,7 @@ typename std::enable_if<
    sizeof(T) <= sizeof(unsigned int)),
   unsigned int>::type
   findFirstSet(T x) {
-#ifdef _MSC_VER
-  unsigned long index;
-  return _BitScanForward(&index, x) ? index : 0;
-#else
   return __builtin_ffs(x);
-#endif
 }
 
 template <class T>
@@ -117,12 +105,7 @@ typename std::enable_if<
    sizeof(T) <= sizeof(unsigned long)),
   unsigned int>::type
   findFirstSet(T x) {
-#ifdef _MSC_VER
-  unsigned long index;
-  return _BitScanForward(&index, x) ? index : 0;
-#else
   return __builtin_ffsl(x);
-#endif
 }
 
 template <class T>
@@ -134,12 +117,7 @@ typename std::enable_if<
    sizeof(T) <= sizeof(unsigned long long)),
   unsigned int>::type
   findFirstSet(T x) {
-#ifdef _MSC_VER
-  unsigned long index;
-  return _BitScanForward64(&index, x) ? index : 0;
-#else
   return __builtin_ffsll(x);
-#endif
 }
 
 template <class T>
@@ -164,18 +142,7 @@ typename std::enable_if<
    sizeof(T) <= sizeof(unsigned int)),
   unsigned int>::type
   findLastSet(T x) {
-#ifdef _MSC_VER
-  unsigned long index;
-  int clz;
-  if (_BitScanReverse(&index, x)) {
-    clz = static_cast<int>(31 - index);
-  } else {
-    clz = 32;
-  }
-  return x ? 8 * sizeof(unsigned int) - clz : 0;
-#else
   return x ? 8 * sizeof(unsigned int) - __builtin_clz(x) : 0;
-#endif
 }
 
 template <class T>
@@ -187,18 +154,7 @@ typename std::enable_if<
    sizeof(T) <= sizeof(unsigned long)),
   unsigned int>::type
   findLastSet(T x) {
-#ifdef _MSC_VER
-  unsigned long index;
-  int clz;
-  if (_BitScanReverse(&index, x)) {
-    clz = static_cast<int>(31 - index);
-  } else {
-    clz = 32;
-  }
-  return x ? 8 * sizeof(unsigned int) - clz : 0;
-#else
   return x ? 8 * sizeof(unsigned long) - __builtin_clzl(x) : 0;
-#endif
 }
 
 template <class T>
@@ -210,18 +166,7 @@ typename std::enable_if<
    sizeof(T) <= sizeof(unsigned long long)),
   unsigned int>::type
   findLastSet(T x) {
-#ifdef _MSC_VER
-  unsigned long index;
-  unsigned long long clz;
-  if (_BitScanReverse(&index, x)) {
-    clz = static_cast<unsigned long long>(63 - index);
-  } else {
-    clz = 64;
-  }
-  return x ? 8 * sizeof(unsigned long long) - clz : 0;
-#else
   return x ? 8 * sizeof(unsigned long long) - __builtin_clzll(x) : 0;
-#endif
 }
 
 template <class T>