Update comments

src/Nethermind/Nethermind.Core/Crypto/KeccakCache.cs

@@ -99,7 +99,8 @@ public static ValueHash256 Compute(ReadOnlySpan<byte> input)
 
         // Try lock and memoize
         int length = Volatile.Read(ref e.LockAndLength);
-        // Negative value means that the entry is locked, set to int.MinValue to avoid confusion empty entry.
+        // Negative value means that the entry is locked, set to int.MinValue to avoid confusion empty entry,
+        // since we are overwriting it anyway e.g. -0 would not be a reliable locked state.
         if (length >= 0 && Interlocked.CompareExchange(ref e.LockAndLength, int.MinValue, length) == length)
         {
             e.Hash = fast;
@@ -135,13 +136,12 @@ private struct Entry
         private const int ValueStart = Size - ValueHash256.MemorySize;
         public const int MaxPayloadLength = ValueStart - PayloadStart;
 
+        /// <summary>
+        /// Length is always positive so we can use a negative length to indicate that it is locked.
+        /// </summary>
         [FieldOffset(0)]
         public int LockAndLength;
 
-        /// <summary>
-        /// The mix of hash and length allows for a fast comparison and a single volatile read.
-        /// The length is encoded as the low part, while the hash as the high part of uint.
-        /// </summary>
         [FieldOffset(4)]
         public int Hash;