From 6dba6cf1f8fb07847d0e5036557679a202a4d9c6 Mon Sep 17 00:00:00 2001
From: "WINDEV2110EVAL\\User" <jubilant-enigma@private.com>
Date: Mon, 3 Jan 2022 14:45:35 -0800
Subject: [PATCH] Moved HexStringToBytes into a
 SixLabors.ImageSharp.Common.Helpers.HexConverter.

---
 src/ImageSharp/Common/Helpers/HexConverter.cs | 98 +++++++++++++++++++
 src/ImageSharp/Formats/Png/PngDecoderCore.cs  | 92 +----------------
 2 files changed, 101 insertions(+), 89 deletions(-)
 create mode 100644 src/ImageSharp/Common/Helpers/HexConverter.cs

diff --git a/src/ImageSharp/Common/Helpers/HexConverter.cs b/src/ImageSharp/Common/Helpers/HexConverter.cs
new file mode 100644
index 0000000000..c55e9bbd9d
--- /dev/null
+++ b/src/ImageSharp/Common/Helpers/HexConverter.cs
@@ -0,0 +1,98 @@
+// Copyright (c) Six Labors.
+// Licensed under the Apache License, Version 2.0.
+
+using System;
+using System.Runtime.CompilerServices;
+
+namespace SixLabors.ImageSharp.Common.Helpers
+{
+    internal static class HexConverter
+    {
+        /// <summary>
+        /// Parses a hexadecimal string into a byte array without allocations. Throws on non-hexadecimal character.
+        /// Adapted from https://source.dot.net/#System.Private.CoreLib/Convert.cs,c9e4fbeaca708991.
+        /// </summary>
+        /// <param name="chars">The hexadecimal string to parse.</param>
+        /// <param name="bytes">The destination for the parsed bytes. Must be at least <paramref name="chars"/>.Length / 2 bytes long.</param>
+        /// <returns>The number of bytes written to <paramref name="bytes"/>.</returns>
+        public static int HexStringToBytes(ReadOnlySpan<char> chars, Span<byte> bytes)
+        {
+            if ((chars.Length % 2) != 0)
+            {
+                throw new ArgumentException("Input string length must be a multiple of 2", nameof(chars));
+            }
+
+            if ((bytes.Length * 2) < chars.Length)
+            {
+                throw new ArgumentException("Output span must be at least half the length of the input string");
+            }
+            else
+            {
+                // Slightly better performance in the loop below, allows us to skip a bounds check
+                // while still supporting output buffers that are larger than necessary
+                bytes = bytes.Slice(0, chars.Length / 2);
+            }
+
+            [MethodImpl(MethodImplOptions.AggressiveInlining)]
+            static int FromChar(int c)
+            {
+                // Map from an ASCII char to its hex value, e.g. arr['b'] == 11. 0xFF means it's not a hex digit.
+                // This doesn't actually allocate.
+                ReadOnlySpan<byte> charToHexLookup = new byte[]
+                {
+                    0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, // 15
+                    0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, // 31
+                    0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, // 47
+                    0x0,  0x1,  0x2,  0x3,  0x4,  0x5,  0x6,  0x7,  0x8,  0x9,  0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, // 63
+                    0xFF, 0xA,  0xB,  0xC,  0xD,  0xE,  0xF,  0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, // 79
+                    0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, // 95
+                    0xFF, 0xa,  0xb,  0xc,  0xd,  0xe,  0xf,  0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, // 111
+                    0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, // 127
+                    0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, // 143
+                    0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, // 159
+                    0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, // 175
+                    0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, // 191
+                    0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, // 207
+                    0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, // 223
+                    0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, // 239
+                    0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, // 255
+                };
+
+                return c >= charToHexLookup.Length ? 0xFF : charToHexLookup[c];
+            }
+
+            // See https://source.dot.net/#System.Private.CoreLib/HexConverter.cs,4681d45a0aa0b361
+            int i = 0;
+            int j = 0;
+            int byteLo = 0;
+            int byteHi = 0;
+            while (j < bytes.Length)
+            {
+                byteLo = FromChar(chars[i + 1]);
+                byteHi = FromChar(chars[i]);
+
+                // byteHi hasn't been shifted to the high half yet, so the only way the bitwise or produces this pattern
+                // is if either byteHi or byteLo was not a hex character.
+                if ((byteLo | byteHi) == 0xFF)
+                {
+                    break;
+                }
+
+                bytes[j++] = (byte)((byteHi << 4) | byteLo);
+                i += 2;
+            }
+
+            if (byteLo == 0xFF)
+            {
+                i++;
+            }
+
+            if ((byteLo | byteHi) == 0xFF)
+            {
+                throw new ArgumentException("Input string contained non-hexadecimal characters", nameof(chars));
+            }
+
+            return j;
+        }
+    }
+}
diff --git a/src/ImageSharp/Formats/Png/PngDecoderCore.cs b/src/ImageSharp/Formats/Png/PngDecoderCore.cs
index 182d6e7bea..708cd7f5f4 100644
--- a/src/ImageSharp/Formats/Png/PngDecoderCore.cs
+++ b/src/ImageSharp/Formats/Png/PngDecoderCore.cs
@@ -11,6 +11,7 @@ using System.Runtime.CompilerServices;
 using System.Runtime.InteropServices;
 using System.Text;
 using System.Threading;
+using SixLabors.ImageSharp.Common.Helpers;
 using SixLabors.ImageSharp.Compression.Zlib;
 using SixLabors.ImageSharp.Formats.Png.Chunks;
 using SixLabors.ImageSharp.Formats.Png.Filters;
@@ -1093,7 +1094,7 @@ namespace SixLabors.ImageSharp.Formats.Png
                     tempExifBuf = new byte[exifHeader.Length];
                 }
 
-                HexStringToBytes(dataSpan.Slice(0, exifHeader.Length * 2), tempExifBuf);
+                HexConverter.HexStringToBytes(dataSpan.Slice(0, exifHeader.Length * 2), tempExifBuf);
                 if (!tempExifBuf.AsSpan().Slice(0, exifHeader.Length).SequenceEqual(exifHeader))
                 {
                     // Exif header in the hex data is not valid
@@ -1115,7 +1116,7 @@ namespace SixLabors.ImageSharp.Formats.Png
                         lineSpan = dataSpan.Slice(0, newlineIndex);
                     }
 
-                    i += HexStringToBytes(lineSpan, exifBlob.AsSpan().Slice(i));
+                    i += HexConverter.HexStringToBytes(lineSpan, exifBlob.AsSpan().Slice(i));
 
                     dataSpan = dataSpan.Slice(newlineIndex + 1);
                 }
@@ -1163,93 +1164,6 @@ namespace SixLabors.ImageSharp.Formats.Png
 #pragma warning restore IDE0022 // Use expression body for methods
         }
 
-        /// <summary>
-        /// Parses a hexadecimal string into a byte array without allocations. Throws on non-hexadecimal character.
-        /// Adapted from https://source.dot.net/#System.Private.CoreLib/Convert.cs,c9e4fbeaca708991.
-        /// </summary>
-        /// <param name="chars">The hexadecimal string to parse.</param>
-        /// <param name="bytes">The destination for the parsed bytes. Must be at least <paramref name="chars"/>.Length / 2 bytes long.</param>
-        /// <returns>The number of bytes written to <paramref name="bytes"/>.</returns>
-        private static int HexStringToBytes(ReadOnlySpan<char> chars, Span<byte> bytes)
-        {
-            if ((chars.Length % 2) != 0)
-            {
-                throw new ArgumentException("Input string length must be a multiple of 2", nameof(chars));
-            }
-
-            if ((bytes.Length * 2) < chars.Length)
-            {
-                throw new ArgumentException("Output span must be at least half the length of the input string");
-            }
-            else
-            {
-                // Slightly better performance in the loop below, allows us to skip a bounds check
-                // while still supporting output buffers that are larger than necessary
-                bytes = bytes.Slice(0, chars.Length / 2);
-            }
-
-            [MethodImpl(MethodImplOptions.AggressiveInlining)]
-            static int FromChar(int c)
-            {
-                // Map from an ASCII char to its hex value, e.g. arr['b'] == 11. 0xFF means it's not a hex digit.
-                // This doesn't actually allocate.
-                ReadOnlySpan<byte> charToHexLookup = new byte[]
-                {
-                    0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, // 15
-                    0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, // 31
-                    0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, // 47
-                    0x0,  0x1,  0x2,  0x3,  0x4,  0x5,  0x6,  0x7,  0x8,  0x9,  0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, // 63
-                    0xFF, 0xA,  0xB,  0xC,  0xD,  0xE,  0xF,  0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, // 79
-                    0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, // 95
-                    0xFF, 0xa,  0xb,  0xc,  0xd,  0xe,  0xf,  0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, // 111
-                    0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, // 127
-                    0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, // 143
-                    0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, // 159
-                    0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, // 175
-                    0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, // 191
-                    0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, // 207
-                    0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, // 223
-                    0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, // 239
-                    0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, // 255
-                };
-
-                return c >= charToHexLookup.Length ? 0xFF : charToHexLookup[c];
-            }
-
-            // See https://source.dot.net/#System.Private.CoreLib/HexConverter.cs,4681d45a0aa0b361
-            int i = 0;
-            int j = 0;
-            int byteLo = 0;
-            int byteHi = 0;
-            while (j < bytes.Length)
-            {
-                byteLo = FromChar(chars[i + 1]);
-                byteHi = FromChar(chars[i]);
-
-                // byteHi hasn't been shifted to the high half yet, so the only way the bitwise or produces this pattern
-                // is if either byteHi or byteLo was not a hex character.
-                if ((byteLo | byteHi) == 0xFF)
-                {
-                    break;
-                }
-
-                bytes[j++] = (byte)((byteHi << 4) | byteLo);
-                i += 2;
-            }
-
-            if (byteLo == 0xFF)
-            {
-                i++;
-            }
-
-            if ((byteLo | byteHi) == 0xFF)
-            {
-                throw new ArgumentException("Input string contained non-hexadecimal characters", nameof(chars));
-            }
-
-            return j;
-        }
-
         /// <summary>
         /// Sets the <see cref="ExifProfile"/> in <paramref name="metadata"/> to <paramref name="newProfile"/>,
         /// or copies exif tags if <paramref name="metadata"/> already contains an <see cref="ExifProfile"/>.