Fix log2() accuracy.

Bug 28474248 Change-Id: I61bf28687623437c6b9b383dc189ffa28ad24c22 Reviewed-on: https://swiftshader-review.googlesource.com/5330Tested-by: Nicolas Capens <capn@google.com> Reviewed-by: Alexis Hétu <sugoi@google.com> Reviewed-by: Nicolas Capens <capn@google.com>

Fix log2() accuracy.
e206543e · Nicolas Capens · a0600301 · e206543e
Commit e206543e authored May 09, 2016 by Nicolas Capens
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Math.hpp src/Common/Math.hpp +1 -3

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--- a/src/Common/Math.hpp
+++ b/src/Common/Math.hpp
@@ -158,9 +158,7 @@ namespace sw

 	inline float log2(float x)
 	{
-		unsigned int y = (*(unsigned int*)&x);
-
-		return (float)((y & 0x7F800000) >> 23) - 127 + (float)((*(unsigned int*)&x) & 0x007FFFFF) / 16777216.0f;
+		return logf(x) * 1.44269504f;   // 1.0 / log[e](2)
 	}

 	inline bool isPow2(int x)