use a constant for stack max alloc threshold

Author: ssg

src/Base16.cs

@@ -214,7 +214,7 @@ public string Encode(ReadOnlySpan<byte> bytes)
         }
 
         int outputLen = GetSafeCharCountForEncoding(bytes);
-        Span<char> output = outputLen < 1024 ? stackalloc char[outputLen] : new char[outputLen];
+        Span<char> output = outputLen < Bits.SafeStackMaxAllocSize ? stackalloc char[outputLen] : new char[outputLen];
         internalEncode(bytes, output, Alphabet.Value);
         return new string(output);
     }

src/Base32.cs

@@ -211,7 +211,7 @@ public string Encode(ReadOnlySpan<byte> bytes, bool padding)
         // we are ok with slightly larger buffer since the output string will always
         // have the exact length of the output produced.
         int outputLen = GetSafeCharCountForEncoding(bytes);
-        Span<char> output = outputLen < 1024 ? stackalloc char[outputLen] : new char[outputLen];
+        Span<char> output = outputLen < Bits.SafeStackMaxAllocSize ? stackalloc char[outputLen] : new char[outputLen];
         if (!internalEncode(
             bytes,
             output,

src/Base58.cs

@@ -224,7 +224,7 @@ public string Encode(ReadOnlySpan<byte> bytes)
 
         int numZeroes = getZeroCount(bytes);
         int outputLen = getSafeCharCountForEncoding(bytes.Length, numZeroes);
-        Span<char> output = outputLen < 1024 ? stackalloc char[outputLen] : new char[outputLen];
+        Span<char> output = outputLen < Bits.SafeStackMaxAllocSize ? stackalloc char[outputLen] : new char[outputLen];
 
         return internalEncode(bytes, output, numZeroes, out int numCharsWritten)
             ? new string(output[..numCharsWritten])

src/Base85.cs

@@ -76,7 +76,7 @@ public string Encode(ReadOnlySpan<byte> bytes)
         }
 
         int outputLen = GetSafeCharCountForEncoding(bytes);
-        Span<char> output = outputLen < 1024 ? stackalloc char[outputLen] : new char[outputLen];
+        Span<char> output = outputLen < Bits.SafeStackMaxAllocSize ? stackalloc char[outputLen] : new char[outputLen];
 
         return internalEncode(bytes, output, out int numCharsWritten)
             ? new string(output[..numCharsWritten])

src/Bits.cs

@@ -0,0 +1,51 @@
+using System;
+using System.Collections.Generic;
+using System.Text;
+
+namespace SimpleBase
+{
+    /// <summary>
+    /// Helper functions for bit operations.
+    /// </summary>
+    internal static class Bits
+    {
+        /// <summary>
+        /// Safe one-shot maximum amount to be allocated on stack for temporary buffers and alike.
+        /// </summary>
+        internal const int SafeStackMaxAllocSize = 1024;
+
+        /// <summary>
+        /// Converts a byte array to a hexadecimal string.
+        /// </summary>
+        /// <param name="bytes"></param>
+        /// <returns></returns>
+        internal static ulong BigEndianBytesToUInt64(ReadOnlySpan<byte> bytes)
+        {
+            if (bytes.Length > sizeof(ulong))
+            {
+                throw new ArgumentOutOfRangeException(nameof(bytes), "Byte array too long to convert to UInt64");
+            }
+
+            ulong result = 0;
+            for (int i = 0; i < bytes.Length; i++)
+            {
+                result = (result << 8) | bytes[i];
+            }
+            return result;
+        }
+
+        internal static void UInt64ToBigEndianBytes(ulong value, Span<byte> output)
+        {
+            if (output.Length < sizeof(ulong))
+            {
+                throw new ArgumentException("Output is too small", nameof(output));
+            }
+            int byteCount = sizeof(ulong);
+            for (int i = byteCount - 1; i >= 0; i--)
+            {
+                output[i] = (byte)(value & 0xFF);
+                value >>= 8;
+            }
+        }
+    }
+}