Fix exp2 for integer input.

exp2(x) should be exact for integer values of x. For example exp(1.0)
should produce 2.0.

Change-Id: I9d6d1d388c23e813e09b7b5788c929ff07189357
Reviewed-on: https://swiftshader-review.googlesource.com/16188
Tested-by: Nicolas Capens <nicolascapens@google.com>
Reviewed-by: Alexis Hétu <sugoi@google.com>

src/Shader/ShaderCore.cpp

diff --git a/src/Shader/ShaderCore.cpp b/src/Shader/ShaderCore.cpp
index 559208c..c763404 100644
--- a/src/Shader/ShaderCore.cpp
+++ b/src/Shader/ShaderCore.cpp
@@ -139,7 +139,7 @@
 		x1 *= x0;
 		x1 += As<Float4>(Int4(0x3F31727B));   // 6.9315308e-1f
 		x1 *= x0;
-		x1 += As<Float4>(Int4(0x3F7FFFFF));   // 9.9999994e-1f
+		x1 += Float4(1.0f);
 		x1 *= As<Float4>(x2);
 
 		return x1;