Enable constant folding on UnpackHalf2x16 instructions

Ryujinx.Graphics/Shader/Translation/Optimizations/ConstantFolding.cs

@@ -188,6 +188,10 @@ namespace Ryujinx.Graphics.Shader.Translation.Optimizations
                 case Instruction.Subtract:
                     EvaluateBinary(operation, (x, y) => x - y);
                     break;
+
+                case Instruction.UnpackHalf2x16:
+                    UnpackHalf2x16(operation);
+                    break;
             }
         }
 
@@ -229,6 +233,15 @@ namespace Ryujinx.Graphics.Shader.Translation.Optimizations
             return value.Extract(lsb, length);
         }
 
+        private static void UnpackHalf2x16(Operation operation)
+        {
+            int value = operation.GetSource(0).Value;
+
+            value = (value >> operation.ComponentIndex * 16) & 0xffff;
+
+            operation.TurnIntoCopy(ConstF(HalfConversion.HalfToSingle(value)));
+        }
+
         private static void FPNegate(Operation operation)
         {
             float value = operation.GetSource(0).AsFloat();

Ryujinx.Graphics/Shader/Translation/Optimizations/HalfConversion.cs

@@ -0,0 +1,47 @@
+using System;
+
+namespace Ryujinx.Graphics.Shader.Translation.Optimizations
+{
+    static class HalfConversion
+    {
+        public static float HalfToSingle(int value)
+        {
+            int mantissa = (value >> 0)  & 0x3ff;
+            int exponent = (value >> 10) & 0x1f;
+            int sign     = (value >> 15) & 0x1;
+
+            if (exponent == 0x1f)
+            {
+                //NaN or Infinity.
+                mantissa <<= 13;
+                exponent   = 0xff;
+            }
+            else if (exponent != 0 || mantissa != 0 )
+            {
+                if (exponent == 0)
+                {
+                    //Denormal.
+                    int e = -1;
+                    int m = mantissa;
+
+                    do
+                    {
+                        e++;
+                        m <<= 1;
+                    }
+                    while ((m & 0x400) == 0);
+
+                    mantissa = m & 0x3ff;
+                    exponent = e;
+                }
+
+                mantissa <<= 13;
+                exponent   = 127 - 15 + exponent;
+            }
+
+            int output = (sign << 31) | (exponent << 23) | mantissa;
+
+            return BitConverter.Int32BitsToSingle(output);
+        }
+    }
+}