From 056d59e862a11c9f841a08fbbdfd1a805b098f29 Mon Sep 17 00:00:00 2001
From: assiduous <assiduous@diligentgraphics.com>
Date: Sat, 11 Apr 2020 22:43:32 -0700
Subject: MathLib: improved FastFloat implementation

---
 Common/interface/BasicMath.hpp | 23 +++++++++++++++++++++--
 1 file changed, 21 insertions(+), 2 deletions(-)

(limited to 'Common/interface')

diff --git a/Common/interface/BasicMath.hpp b/Common/interface/BasicMath.hpp
index 757244e1..25e99240 100644
--- a/Common/interface/BasicMath.hpp
+++ b/Common/interface/BasicMath.hpp
@@ -1942,13 +1942,32 @@ inline Uint32 F4Color_To_RGBA8Unorm(const float4& f4Color)
     return RGBA8U;
 }
 
+template <typename T>
+struct _FastFloatIntermediateType
+{
+};
+
+template <>
+struct _FastFloatIntermediateType<float>
+{
+    // All floats that have fractional part are representable as 32-bit int
+    using Type = Int32;
+};
+
+template <>
+struct _FastFloatIntermediateType<double>
+{
+    // All doubles that have fractional part are representable as 64-bit int
+    using Type = Int64;
+};
 
 // At least on MSVC std::floor is an actual function call into ucrtbase.dll.
-// For floats/doubles that fit into Int64 representable range we can do much better.
+// All floats/doubles that have fractional parts also fit into integer
+// representable range, so we can do much better.
 template <typename T>
 T FastFloor(T x)
 {
-    auto i   = static_cast<Int64>(x);
+    auto i   = static_cast<typename _FastFloatIntermediateType<T>::Type>(x);
     auto flr = static_cast<T>(i);
     //   x         flr    floor(x)  flr <= x
     // +1.0   ->   1.0      1.0       true
-- 
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