Merge pull request #2233 from SixLabors/js/system-half

Use System.Half for HalfTypeHelper

Author: JimBobSquarePants

src/ImageSharp/PixelFormats/HalfTypeHelper.cs

@@ -1,8 +1,7 @@
-// Copyright (c) Six Labors.
+// Copyright (c) Six Labors.
 // Licensed under the Six Labors Split License.
 
 using System.Runtime.CompilerServices;
-using System.Runtime.InteropServices;
 
 namespace SixLabors.ImageSharp.PixelFormats;
 
@@ -17,128 +16,13 @@ internal static class HalfTypeHelper
     /// <param name="value">The float to pack</param>
     /// <returns>The <see cref="ushort"/></returns>
     [MethodImpl(MethodImplOptions.AggressiveInlining)]
-    internal static ushort Pack(float value)
-    {
-        var uif = new Uif { F = value };
-        return Pack(uif.I);
-    }
-
-    /// <summary>
-    /// Packs an <see cref="int"/> into a <see cref="ushort"/>
-    /// </summary>
-    /// <param name="value">The integer to pack.</param>
-    /// <returns>The <see cref="ushort"/></returns>
-    internal static ushort Pack(int value)
-    {
-        int s = (value >> 16) & 0x00008000;
-        int e = ((value >> 23) & 0x000000ff) - (127 - 15);
-        int m = value & 0x007fffff;
-
-        if (e <= 0)
-        {
-            if (e < -10)
-            {
-                return (ushort)s;
-            }
-
-            m |= 0x00800000;
-
-            int t = 14 - e;
-            int a = (1 << (t - 1)) - 1;
-            int b = (m >> t) & 1;
-
-            m = (m + a + b) >> t;
-
-            return (ushort)(s | m);
-        }
-
-        if (e == 0xff - (127 - 15))
-        {
-            if (m == 0)
-            {
-                return (ushort)(s | 0x7c00);
-            }
-
-            m >>= 13;
-            return (ushort)(s | 0x7c00 | m | ((m == 0) ? 1 : 0));
-        }
-
-        m = m + 0x00000fff + ((m >> 13) & 1);
-
-        if ((m & 0x00800000) != 0)
-        {
-            m = 0;
-            e++;
-        }
-
-        if (e > 30)
-        {
-            return (ushort)(s | 0x7c00);
-        }
-
-        return (ushort)(s | (e << 10) | (m >> 13));
-    }
+    internal static ushort Pack(float value) => BitConverter.HalfToUInt16Bits((Half)value);
 
     /// <summary>
     /// Unpacks a <see cref="ushort"/> into a <see cref="float"/>.
     /// </summary>
     /// <param name="value">The value.</param>
     /// <returns>The <see cref="float"/>.</returns>
-    internal static float Unpack(ushort value)
-    {
-        uint result;
-        uint mantissa = (uint)(value & 1023);
-        uint exponent = 0xfffffff2;
-
-        if ((value & -33792) == 0)
-        {
-            if (mantissa != 0)
-            {
-                while ((mantissa & 1024) == 0)
-                {
-                    exponent--;
-                    mantissa <<= 1;
-                }
-
-                mantissa &= 0xfffffbff;
-                result = (((uint)value & 0x8000) << 16) | ((exponent + 127) << 23) | (mantissa << 13);
-            }
-            else
-            {
-                result = (uint)((value & 0x8000) << 16);
-            }
-        }
-        else
-        {
-            result = (((uint)value & 0x8000) << 16) | ((((((uint)value >> 10) & 0x1f) - 15) + 127) << 23) | (mantissa << 13);
-        }
-
-        var uif = new Uif { U = result };
-        return uif.F;
-    }
-
-    /// <summary>
-    /// Maps the position of number types in memory
-    /// </summary>
-    [StructLayout(LayoutKind.Explicit)]
-    private struct Uif
-    {
-        /// <summary>
-        /// The float.
-        /// </summary>
-        [FieldOffset(0)]
-        public float F;
-
-        /// <summary>
-        /// The integer.
-        /// </summary>
-        [FieldOffset(0)]
-        public int I;
-
-        /// <summary>
-        /// The unsigned integer.
-        /// </summary>
-        [FieldOffset(0)]
-        public uint U;
-    }
+    [MethodImpl(MethodImplOptions.AggressiveInlining)]
+    internal static float Unpack(ushort value) => (float)BitConverter.UInt16BitsToHalf(value);
 }