Optimize the ToHexString

src/Neo.Cryptography.BLS12_381/Neo.Cryptography.BLS12_381.csproj

@@ -13,4 +13,8 @@
     <PackageReference Include="System.Runtime.CompilerServices.Unsafe" Version="6.0.0" />
   </ItemGroup>
 
+  <ItemGroup>
+    <ProjectReference Include="..\Neo.Extensions\Neo.Extensions.csproj" />
+  </ItemGroup>
+
 </Project>

src/Neo.Cryptography.BLS12_381/Scalar.cs

@@ -9,6 +9,7 @@
 // Redistribution and use in source and binary forms with or without
 // modifications are permitted.
 
+using Neo.Extensions;
 using System.Diagnostics.CodeAnalysis;
 using System.Runtime.CompilerServices;
 using System.Runtime.InteropServices;
@@ -119,11 +120,11 @@ private Span<ulong> GetSpanU64()
 
     public override string ToString()
     {
-        byte[] bytes = ToArray();
-        StringBuilder sb = new();
+        var bytes = ToArray();
+
+        StringBuilder sb = new(2 + (bytes.Length * 2));
         sb.Append("0x");
-        for (int i = bytes.Length - 1; i >= 0; i--)
-            sb.AppendFormat("{0:x2}", bytes[i]);
+        sb.Append(bytes.ToHexString(true));
         return sb.ToString();
     }
 

src/Neo.Extensions/ByteExtensions.cs

@@ -10,23 +10,36 @@
 // modifications are permitted.
 
 using System;
+using System.Runtime.CompilerServices;
 using System.Text;
 
 namespace Neo.Extensions
 {
     public static class ByteExtensions
     {
+        private const string s_hexChars = "0123456789abcdef";
+
         /// <summary>
         /// Converts a byte array to hex <see cref="string"/>.
         /// </summary>
         /// <param name="value">The byte array to convert.</param>
         /// <returns>The converted hex <see cref="string"/>.</returns>
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
         public static string ToHexString(this byte[] value)
         {
-            StringBuilder sb = new();
-            foreach (var b in value)
-                sb.AppendFormat("{0:x2}", b);
-            return sb.ToString();
+#if NET9_0_OR_GREATER
+            return Convert.ToHexStringLower(value);
+#else
+            return string.Create(value.Length * 2, value, (span, bytes) =>
+            {
+                for (var i = 0; i < bytes.Length; i++)
+                {
+                    var b = bytes[i];
+                    span[i * 2] = s_hexChars[b >> 4];
+                    span[i * 2 + 1] = s_hexChars[b & 0xF];
+                }
+            });
+#endif
         }
 
         /// <summary>
@@ -35,25 +48,44 @@ public static string ToHexString(this byte[] value)
         /// <param name="value">The byte array to convert.</param>
         /// <param name="reverse">Indicates whether it should be converted in the reversed byte order.</param>
         /// <returns>The converted hex <see cref="string"/>.</returns>
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
         public static string ToHexString(this byte[] value, bool reverse = false)
         {
-            StringBuilder sb = new();
-            for (var i = 0; i < value.Length; i++)
-                sb.AppendFormat("{0:x2}", value[reverse ? value.Length - i - 1 : i]);
-            return sb.ToString();
+            if (!reverse)
+                return ToHexString(value);
+
+            return string.Create(value.Length * 2, value, (span, bytes) =>
+            {
+                for (var i = 0; i < bytes.Length; i++)
+                {
+                    var b = bytes[bytes.Length - i - 1];
+                    span[i * 2] = s_hexChars[b >> 4];
+                    span[i * 2 + 1] = s_hexChars[b & 0xF];
+                }
+            });
         }
 
         /// <summary>
         /// Converts a byte array to hex <see cref="string"/>.
         /// </summary>
         /// <param name="value">The byte array to convert.</param>
         /// <returns>The converted hex <see cref="string"/>.</returns>
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
         public static string ToHexString(this ReadOnlySpan<byte> value)
         {
-            StringBuilder sb = new();
-            foreach (var b in value)
-                sb.AppendFormat("{0:x2}", b);
+#if NET9_0_OR_GREATER
+            return Convert.ToHexStringLower(value);
+#else
+            // string.Create with ReadOnlySpan<char> not supported in NET5 or lower
+            var sb = new StringBuilder(value.Length * 2);
+            for (var i = 0; i < value.Length; i++)
+            {
+                var b = value[i];
+                sb.Append(s_hexChars[b >> 4]);
+                sb.Append(s_hexChars[b & 0xF]);
+            }
             return sb.ToString();
+#endif
         }
     }
 }