From 1e35b99f74eed1d33b9b52f2bd517a3b40788437 Mon Sep 17 00:00:00 2001
From: Merry <MerryMage@users.noreply.github.com>
Date: Thu, 12 Jul 2018 19:51:02 +0100
Subject: [PATCH] AInstEmitSimdCvt: Half-precision to single-precision
 conversion (#235)

---
 Instruction/AInstEmitSimdCvt.cs |  8 ++++----
 Instruction/ASoftFloat.cs       | 36 +++++++++++++++++++++++++++++++++
 2 files changed, 40 insertions(+), 4 deletions(-)

diff --git a/Instruction/AInstEmitSimdCvt.cs b/Instruction/AInstEmitSimdCvt.cs
index 98bb972..da58474 100644
--- a/Instruction/AInstEmitSimdCvt.cs
+++ b/Instruction/AInstEmitSimdCvt.cs
@@ -45,10 +45,10 @@ namespace ChocolArm64.Instruction
             {
                 if (SizeF == 0)
                 {
-                    //TODO: This need the half precision floating point type,
-                    //that is not yet supported on .NET. We should probably
-                    //do our own implementation on the meantime.
-                    throw new NotImplementedException();
+                    EmitVectorExtractZx(Context, Op.Rn, Part + Index, 1);
+                    Context.Emit(OpCodes.Conv_U2);
+
+                    Context.EmitCall(typeof(ASoftFloat), nameof(ASoftFloat.ConvertHalfToSingle));
                 }
                 else /* if (SizeF == 1) */
                 {
diff --git a/Instruction/ASoftFloat.cs b/Instruction/ASoftFloat.cs
index e63c82b..27f4f7f 100644
--- a/Instruction/ASoftFloat.cs
+++ b/Instruction/ASoftFloat.cs
@@ -225,5 +225,41 @@ namespace ChocolArm64.Instruction
 
             return 2.0 + op1 * op2;
         }
+
+        public static float ConvertHalfToSingle(ushort x)
+        {
+            uint x_sign = (uint)(x >> 15) & 0x0001;
+            uint x_exp = (uint)(x >> 10) & 0x001F;
+            uint x_mantissa = (uint)x & 0x03FF;
+
+            if (x_exp == 0 && x_mantissa == 0)
+            {
+                // Zero
+                return BitConverter.Int32BitsToSingle((int)(x_sign << 31));
+            }
+
+            if (x_exp == 0x1F)
+            {
+                // NaN or Infinity
+                return BitConverter.Int32BitsToSingle((int)((x_sign << 31) | 0x7F800000 | (x_mantissa << 13)));
+            }
+
+            int exponent = (int)x_exp - 15;
+
+            if (x_exp == 0)
+            {
+                // Denormal
+                x_mantissa <<= 1;
+                while ((x_mantissa & 0x0400) == 0)
+                {
+                    x_mantissa <<= 1;
+                    exponent--;
+                }
+                x_mantissa &= 0x03FF;
+            }
+
+            uint new_exp = (uint)((exponent + 127) & 0xFF) << 23;
+            return BitConverter.Int32BitsToSingle((int)((x_sign << 31) | new_exp | (x_mantissa << 13)));
+        }
     }
 }
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