prozolic · prozolic · May 11, 2026 · May 11, 2026 · May 11, 2026
diff --git a/src/CsToml/Error/ExceptionHelper.cs b/src/CsToml/Error/ExceptionHelper.cs
diff --git a/src/CsToml/Extension/CollectionExtensions.cs b/src/CsToml/Extension/CollectionExtensions.cs
@@ -1,4 +1,5 @@
-using System.Runtime.CompilerServices;
+using System.Diagnostics;
+using System.Runtime.CompilerServices;
 using System.Runtime.InteropServices;
 
 
@@ -9,21 +10,21 @@ internal static class CollectionExtensions
     [MethodImpl(MethodImplOptions.AggressiveInlining)]
     public static ref T At<T>(this Span<T> span, int index)
     {
-        // Avoid range check.
+        Debug.Assert((uint)index < (uint)span.Length, $"Index {index} out of range [0, {span.Length})");
         return ref Unsafe.Add<T>(ref MemoryMarshal.GetReference(span), index);
     }
 
     [MethodImpl(MethodImplOptions.AggressiveInlining)]
     public static ref T At<T>(this ReadOnlySpan<T> span, int index)
     {
-        // Avoid range check.
+        Debug.Assert((uint)index < (uint)span.Length, $"Index {index} out of range [0, {span.Length})");
         return ref Unsafe.Add<T>(ref MemoryMarshal.GetReference(span), index);
     }
 
     [MethodImpl(MethodImplOptions.AggressiveInlining)]
     public static ref T At<T>(this T[] array, int index)
     {
-        // Avoid range check.
+        Debug.Assert((uint)index < (uint)array.Length, $"Index {index} out of range [0, {array.Length})");
         return ref Unsafe.Add<T>(ref MemoryMarshal.GetArrayDataReference(array), index);
     }
 }

diff --git a/src/CsToml/TomlCodes.cs b/src/CsToml/TomlCodes.cs
@@ -2,6 +2,7 @@
 using CsToml.Error;
 using CsToml.Extension;
 using CsToml.Utility;
+using System.Buffers;
 using System.Diagnostics;
 using System.Runtime.CompilerServices;
 using System.Text;
@@ -58,28 +59,55 @@ internal static int ParseHex(byte hexNumber)
                 -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, // 0xe0 - 0xef
                 -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, // 0xf0 - 0xff
             ];
-            return hexTable[hexNumber];
+            return hexTable.At(hexNumber);
         }
 
-        internal static int DigitsDecimalUnroll4(long value)
+        private static readonly ulong[] zeroOrPowersOf10 =
+        [
+            0,
+            0,
+            10,
+            100,
+            1000,
+            10000,
+            100000,
+            1000000,
+            10000000,
+            100000000,
+            1000000000,
+            10000000000,
+            100000000000,
+            1000000000000,
+            10000000000000,
+            100000000000000,
+            1000000000000000,
+            10000000000000000,
+            100000000000000000,
+            1000000000000000000,
+            10000000000000000000
+        ];
+
+        // https://github.com/fmtlib/fmt/blob/662adf4f33346ba9aba8b072194e319869ede54a/include/fmt/format.h#L1124
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        internal static int CountDigitsForInt64(long value)
         {
             // long.MinValue raises an OverflowException, so fixed support
             // https://learn.microsoft.com/en-us/dotnet/api/system.math.abs?view=net-8.0#system-math-abs(system-int64)
             if (value == long.MinValue)
                 return 19;
 
-            var number = 1;
-            value = Math.Abs(value);
+            ulong absValue = (ulong)(value < 0 ? -value : value);
 
-            for (; ; )
-            {
-                if (value < 10) return number;
-                if (value < 100) return number + 1;
-                if (value < 1000) return number + 2;
-                if (value < 10000) return number + 3;
-                value /= 10000;
-                number += 4;
-            }
+            ReadOnlySpan<byte> bsr2log10 =
+            [
+                 1,  1,  1,  2,  2,  2,  3,  3,  3,  4,  4,  4,  4,  5,  5,  5,
+                 6,  6,  6,  7,  7,  7,  7,  8,  8,  8,  9,  9,  9, 10, 10, 10,
+                10, 11, 11, 11, 12, 12, 12, 13, 13, 13, 13, 14, 14, 14, 15, 15,
+                15, 16, 16, 16, 16, 17, 17, 17, 18, 18, 18, 19, 19, 19, 19, 20
+            ];
+
+            int t = bsr2log10.At((int)ulong.Log2(absValue));
+            return (int)(t - (absValue < zeroOrPowersOf10.At(t) ? 1 : 0));
         }
     }
 
@@ -181,7 +209,7 @@ internal static bool IsEscape(byte rawByte) // U+0000-U+0008,U+000A-U+001F,U+007
             false, false, false, false, false, false, false, false, false, false, false, false, false, false, false, false, // 0xe0 - 0xef
             false, false, false, false, false, false, false, false, false, false, false, false, false, false, false, false, // 0xf0 - 0xff
         ];
-        return escapeTable[rawByte];
+        return escapeTable.At(rawByte);
     }
 
     [MethodImpl(MethodImplOptions.AggressiveInlining)]
@@ -206,7 +234,7 @@ internal static bool IsEscapeSequence(byte rawByte)
             false, false, false, false, false, false, false, false, false, false, false, false, false, false, false, false, // 0xe0 - 0xef
             false, false, false, false, false, false, false, false, false, false, false, false, false, false, false, false, // 0xf0 - 0xff
         ];
-        return escapeSequenceTable[rawByte];
+        return escapeSequenceTable.At(rawByte);
     }
 
     [MethodImpl(MethodImplOptions.AggressiveInlining)]
@@ -231,7 +259,7 @@ internal static bool IsBareKey(byte rawByte)
             false, false, false, false, false, false, false, false, false, false, false, false, false, false, false, false, // 0xe0 - 0xef
             false, false, false, false, false, false, false, false, false, false, false, false, false, false, false, false, // 0xf0 - 0xff
         ];
-        return barekeyTable[rawByte];
+        return barekeyTable.At(rawByte);
     }
 
     [MethodImpl(MethodImplOptions.AggressiveInlining)]
@@ -278,6 +306,10 @@ internal static bool IsRightSquareBrackets(byte rawByte)
     internal static bool IsRightBraces(byte rawByte)
         => rawByte == Symbol.RIGHTBRACES;
 
+    internal static ReadOnlySpan<byte> TabOrWhiteSpaceOrNewlineBytes => [Symbol.TAB, Symbol.SPACE, Symbol.LINEFEED, Symbol.CARRIAGE];
+
+    internal static ReadOnlySpan<byte> TabOrWhiteSpaceBytes => [Symbol.TAB, Symbol.SPACE];
+
     [MethodImpl(MethodImplOptions.AggressiveInlining)]
     internal static bool IsTabOrWhiteSpace(byte rawByte)
         => IsTab(rawByte) || IsWhiteSpace(rawByte);
@@ -308,7 +340,7 @@ internal static bool IsNumber(byte rawByte)
             false, false, false, false, false, false, false, false, false, false, false, false, false, false, false, false, // 0xe0 - 0xef
             false, false, false, false, false, false, false, false, false, false, false, false, false, false, false, false, // 0xf0 - 0xff
         ];
-        return numberTable[rawByte];
+        return numberTable.At(rawByte);
     }
 
     [MethodImpl(MethodImplOptions.AggressiveInlining)]
@@ -333,7 +365,7 @@ internal static bool IsBinary(byte rawByte)
             false, false, false, false, false, false, false, false, false, false, false, false, false, false, false, false, // 0xe0 - 0xef
             false, false, false, false, false, false, false, false, false, false, false, false, false, false, false, false, // 0xf0 - 0xff
         ];
-        return binaryTable[rawByte];
+        return binaryTable.At(rawByte);
     }
 
     [MethodImpl(MethodImplOptions.AggressiveInlining)]
@@ -358,7 +390,7 @@ internal static bool IsOctal(byte rawByte)
             false, false, false, false, false, false, false, false, false, false, false, false, false, false, false, false, // 0xe0 - 0xef
             false, false, false, false, false, false, false, false, false, false, false, false, false, false, false, false, // 0xf0 - 0xff
         ];
-        return octalTable[rawByte];
+        return octalTable.At(rawByte);
     }
 
     [MethodImpl(MethodImplOptions.AggressiveInlining)]
@@ -383,7 +415,7 @@ internal static bool IsHex(byte rawByte)
             false, false, false, false, false, false, false, false, false, false, false, false, false, false, false, false, // 0xe0 - 0xef
             false, false, false, false, false, false, false, false, false, false, false, false, false, false, false, false, // 0xf0 - 0xff
         ];
-        return hexTable[rawByte];
+        return hexTable.At(rawByte);
     }
 
     [MethodImpl(MethodImplOptions.AggressiveInlining)]
@@ -409,7 +441,7 @@ internal static bool IsUpperHexAlphabet(byte rawByte)
             false, false, false, false, false, false, false, false, false, false, false, false, false, false, false, false, // 0xe0 - 0xef
             false, false, false, false, false, false, false, false, false, false, false, false, false, false, false, false, // 0xf0 - 0xff
         ];
-        return upperHexAlphabetTable[rawByte];
+        return upperHexAlphabetTable.At(rawByte);
     }
 
     [MethodImpl(MethodImplOptions.AggressiveInlining)]
@@ -435,7 +467,7 @@ internal static bool IsLowerHexAlphabet(byte rawByte)
             false, false, false, false, false, false, false, false, false, false, false, false, false, false, false, false, // 0xe0 - 0xef
             false, false, false, false, false, false, false, false, false, false, false, false, false, false, false, false, // 0xf0 - 0xff
         ];
-        return lowerHexAlphabetTable[rawByte];
+        return lowerHexAlphabetTable.At(rawByte);
     }
 
     [MethodImpl(MethodImplOptions.AggressiveInlining)]
@@ -461,7 +493,7 @@ internal static bool IsAlphabet(byte rawByte)
             false, false, false, false, false, false, false, false, false, false, false, false, false, false, false, false, // 0xe0 - 0xef
             false, false, false, false, false, false, false, false, false, false, false, false, false, false, false, false, // 0xf0 - 0xff
         ];
-        return alphabetTable[rawByte];
+        return alphabetTable.At(rawByte);
     }
 
     [MethodImpl(MethodImplOptions.AggressiveInlining)]

diff --git a/src/CsToml/Utf8TomlDocumentWriter.cs b/src/CsToml/Utf8TomlDocumentWriter.cs
@@ -40,7 +40,7 @@ public ref struct Utf8TomlDocumentWriter<TBufferWriter>
     public readonly bool IsRoot => valueStates.Count == 1 && !valueOnly;
 
     internal Utf8TomlDocumentWriter(ref TBufferWriter bufferWriter, bool valueOnly = false) : this(ref bufferWriter, valueOnly, null)
-    {}
+    { }
 
     internal Utf8TomlDocumentWriter(ref TBufferWriter bufferWriter, bool valueOnly, CsTomlSerializerOptions? options)
     {
@@ -140,7 +140,7 @@ public void WriteBoolean(bool value)
 
     public void WriteInt64(long value)
     {
-        var length = TomlCodes.Number.DigitsDecimalUnroll4(value);
+        var length = TomlCodes.Number.CountDigitsForInt64(value);
         if (value < 0) length++;
 
         value.TryFormat(writer.GetWrittenSpan(length), out int bytesWritten, null, CultureInfo.InvariantCulture);
@@ -183,7 +183,7 @@ internal void WriteInt64InOctalFormat(long value)
         var writtenSpan = writer.GetWrittenSpan(digits);
         var index = digits - 1;
 
-        while (value > 0) 
+        while (value > 0)
         {
             var v = value & 7;
             writtenSpan[index--] = (byte)(TomlCodes.Number.Zero + (byte)v);
@@ -240,7 +240,7 @@ internal void WriteInt64InHexFormat(long value)
 
     public void WriteDouble(double value)
     {
-        switch(value)
+        switch (value)
         {
             case double.NegativeInfinity:
                 WriteBytes("-inf"u8);
@@ -370,7 +370,7 @@ public void WriteDateTimeOffset(DateTimeOffset value)
             {
                 if (value.Microsecond == 0)
                 {
-                    var length = TomlCodes.Number.DigitsDecimalUnroll4(value.Millisecond);
+                    var length = TomlCodes.Number.CountDigitsForInt64(value.Millisecond);
                     switch (length)
                     {
                         case 1:
@@ -397,7 +397,7 @@ public void WriteDateTimeOffset(DateTimeOffset value)
                 }
                 else
                 {
-                    var length = TomlCodes.Number.DigitsDecimalUnroll4(value.Microsecond);
+                    var length = TomlCodes.Number.CountDigitsForInt64(value.Microsecond);
                     switch (length)
                     {
                         case 1:
@@ -434,7 +434,7 @@ public void WriteDateTimeOffset(DateTimeOffset value)
             {
                 if (value.Microsecond == 0)
                 {
-                    var length = TomlCodes.Number.DigitsDecimalUnroll4(value.Millisecond);
+                    var length = TomlCodes.Number.CountDigitsForInt64(value.Millisecond);
                     switch (length)
                     {
                         case 1:
@@ -461,7 +461,7 @@ public void WriteDateTimeOffset(DateTimeOffset value)
                 }
                 else
                 {
-                    var length = TomlCodes.Number.DigitsDecimalUnroll4(value.Microsecond);
+                    var length = TomlCodes.Number.CountDigitsForInt64(value.Microsecond);
                     switch (length)
                     {
                         case 1:
@@ -501,7 +501,7 @@ public void WriteDateTime(DateTime value)
         {
             if (value.Microsecond == 0)
             {
-                var length = TomlCodes.Number.DigitsDecimalUnroll4(value.Millisecond);
+                var length = TomlCodes.Number.CountDigitsForInt64(value.Millisecond);
                 switch (length)
                 {
                     case 1:
@@ -528,7 +528,7 @@ public void WriteDateTime(DateTime value)
             }
             else
             {
-                var length = TomlCodes.Number.DigitsDecimalUnroll4(value.Microsecond);
+                var length = TomlCodes.Number.CountDigitsForInt64(value.Microsecond);
                 switch (length)
                 {
                     case 1:
@@ -572,7 +572,7 @@ public void WriteTimeOnly(TimeOnly value)
         {
             if (value.Microsecond == 0)
             {
-                var length = TomlCodes.Number.DigitsDecimalUnroll4(value.Millisecond);
+                var length = TomlCodes.Number.CountDigitsForInt64(value.Millisecond);
                 switch (length)
                 {
                     case 1:
@@ -599,7 +599,7 @@ public void WriteTimeOnly(TimeOnly value)
             }
             else
             {
-                var length = TomlCodes.Number.DigitsDecimalUnroll4(value.Microsecond);
+                var length = TomlCodes.Number.CountDigitsForInt64(value.Microsecond);
                 switch (length)
                 {
                     case 1:
@@ -713,7 +713,7 @@ internal void WriteKeyInternal(string key)
                     fixed (byte* ptr = &destReference)
                     {
                         var writtenSpan = MemoryMarshal.CreateSpan(ref Unsafe.AsRef<byte>(ptr), bytesWritten);
-                        WriteKeyInternal(writtenSpan, TomlDottedKeyHelper.GetTomlKeyType( writtenSpan, options.Spec.SupportsEscapeSequenceE, options.Spec.SupportsEscapeSequenceX));
+                        WriteKeyInternal(writtenSpan, TomlDottedKeyHelper.GetTomlKeyType(writtenSpan, options.Spec.SupportsEscapeSequenceE, options.Spec.SupportsEscapeSequenceX));
                     }
                 }
             }

diff --git a/src/CsToml/Utility/SpanWriter.cs b/src/CsToml/Utility/SpanWriter.cs
@@ -1,13 +1,11 @@
 using CsToml.Error;
 using System.Runtime.CompilerServices;
-using System.Runtime.InteropServices;
 
 namespace CsToml.Utility;
 
-internal ref struct SpanWriter(Span<byte> buffer)
+internal ref struct SpanWriter(Span<byte> source)
 {
-    private readonly Span<byte> source = buffer;
-    private readonly ref byte refSource = ref MemoryMarshal.GetReference(buffer);
+    private readonly Span<byte> source = source;
     private int written = 0;
 
     public readonly int Written => written;
@@ -17,14 +15,13 @@ internal ref struct SpanWriter(Span<byte> buffer)
     [MethodImpl(MethodImplOptions.AggressiveInlining)]
     public void Write(byte ch)
     {
-        if (written >= source.Length)
+        if ((uint)written >= (uint)source.Length)
         {
             ExceptionHelper.ThrowOverflowDuringParsingOfNumericTypes();
             return;
         }
 
-        ref var v = ref Unsafe.Add(ref refSource, written++);
-        v = ch;
+        source[written++] = ch;
     }
 
 }
diff --git a/src/CsToml/Utility/Utf8Helper.cs b/src/CsToml/Utility/Utf8Helper.cs
@@ -1,8 +1,8 @@
 using CsToml.Error;
 using System.Buffers;
-using System.Numerics;
 using System.Runtime.CompilerServices;
 using System.Runtime.InteropServices;
+using System.Text;
 using System.Text.Unicode;
 
 namespace CsToml.Utility;
@@ -281,7 +281,8 @@ public static bool ContainsEscapeChar(ReadOnlySpan<byte> bytes, bool newline)
     public static void FromUtf16(IBufferWriter<byte> writer, ReadOnlySpan<char> value)
     {
         // buffer size to 3 times worst-case (UTF16 -> UTF8)
-        var maxBufferSize = (value.Length + 1) * 3;
+        // var maxBufferSize = (value.Length + 1) * 3;
+        var maxBufferSize = Encoding.UTF8.GetMaxByteCount(value.Length);
 
         var status = Utf8.FromUtf16(value, writer.GetSpan(maxBufferSize),
             out int charsRead, out int bytesWritten, replaceInvalidSequences: false);
@@ -315,7 +316,7 @@ public static string ToUtf16(ReadOnlySpan<byte> utf8Bytes)
             return string.Empty;
         }
 
-        var maxBufferSize = utf8Bytes.Length * 2;
+        var maxBufferSize = utf8Bytes.Length;
         if (maxBufferSize <= 1024)
         {
             Span<char> bufferBytesSpan = stackalloc char[maxBufferSize];