Disable FMA3 when compiling with VS2013 (#2308)

* Disable FMA3 when compiling with VS2013

* Add Win64 job to AppVeyor CI

appveyor.yml

@@ -7,8 +7,13 @@ environment:
   matrix:
   - Compiler: msvc
     Config: Release
+    Platform: Win32
   - Compiler: msvc
     Config: Debug
+    Platform: Win32
+  - Compiler: msvc
+    Config: Release
+    Platform: Win64
   - Compiler: mingw
     Build: static
   - Compiler: mingw
@@ -38,7 +43,7 @@ build_script:
       if ($env:Compiler -eq "mingw") {
         mingw32-make -j4 sassc
       } else {
-        msbuild /m:4 /p:Configuration=$env:Config sassc\win\sassc.sln
+        msbuild /m:4 /p:"Configuration=$env:Config;Platform=$env:Platform" sassc\win\sassc.sln
       }
 
       # print the branding art
@@ -84,4 +89,3 @@ test_script:
       } else {
         echo "Success!"
       }
-

src/util.cpp

@@ -9,11 +9,22 @@
 
 #include <cmath>
 #include <stdint.h>
+#if defined(_MSC_VER) && _MSC_VER >= 1800 && _MSC_VER < 1900 && defined(_M_X64)
+#include <mutex>
+#endif
 
 namespace Sass {
 
   double round(double val, size_t precision)
   {
+    // Disable FMA3-optimized implementation when compiling with VS2013 for x64 targets
+    // See https://github.com/sass/node-sass/issues/1854 for details
+    // FIXME: Remove this workaround when we switch to VS2015+
+    #if defined(_MSC_VER) && _MSC_VER >= 1800 && _MSC_VER < 1900 && defined(_M_X64)
+      static std::once_flag flag;
+      std::call_once(flag, []() { _set_FMA3_enable(0); });
+    #endif
+
     // https://github.com/sass/sass/commit/4e3e1d5684cc29073a507578fc977434ff488c93
     if (fmod(val, 1) - 0.5 > - std::pow(0.1, precision + 1)) return std::ceil(val);
     else if (fmod(val, 1) - 0.5 > std::pow(0.1, precision)) return std::floor(val);