Improve performance by improving the handling of hashes

Performance is improved in the following ways:
  1. Eliminate Hash.ComputeHash() that returns a string, and
     Hash.Sum() that converts the string to an array of hash bytes
  2. Avoid the use of Enumerable.Skip() and Enumerable.Take()
  3. Avoid the use of Array.Reverse() on little-endian architectures

Change library to use HashAlgorithm directly.  Remove Hash.cs, Hash128.cs
and their corresponding tests.

Add Utils.HashBytesToUInt32() and Utils.HashBytesToUInt64() functions
that convert a set of .NET hash bytes into a uint or ulong regardless
of the endianness of the architecture.

Fix Utils.HashKernel128() to conform to how HashKernel() works,
and fix corresponding unit tests.

Add TestProbabilisticDataStructures.TestHashKernelFNV1()
that confirms that the HashKernel() function returns
the same values as the HashKernel() function in
https://github.com/tylertreat/BoomFilters running in Go.

Move the original Hash.ComputeHash() that returns a string
to Utils.ComputeHashAsString().  This function is no longer
used by the library, but the unit tests that use it remain.

ProbabilisticDataStructures/CuckooBloomFilter.cs

@@ -384,38 +384,23 @@ private bool Insert(uint i1, uint i2, byte[] f)
         /// fingerprint for the given data</returns>
         private Components GetComponents(byte[] data)
         {
-            var hash = this.ComputeHash(data);
+            var hash = Hash.ComputeHash(data);
             var f = hash.Take((int)this.F).ToArray();
             var i1 = this.ComputeHashSum32(hash);
             var i2 = this.ComputeHashSum32(f);
 
             return Components.Create(f, i1, i2);
         }
 
-        /// <summary>
-        /// Returns a 32-bit hash value for the given data.
-        /// </summary>
-        /// <param name="data">Data</param>
-        /// <returns>32-bit hash value</returns>
-        private byte[] ComputeHash(byte[] data)
-        {
-            var hash = new Hash(this.Hash);
-            hash.ComputeHash(data);
-            var sum = hash.Sum();
-            return sum;
-        }
-
         /// <summary>
         /// Returns the sum of the hash.
         /// </summary>
         /// <param name="data">Data</param>
         /// <returns>32-bit hash value</returns>
         private uint ComputeHashSum32(byte[] data)
         {
-            var hash = new Hash(this.Hash);
-            hash.ComputeHash(data);
-            var sum = hash.Sum();
-            return Utils.ToBigEndianUInt32(sum);
+            var sum = Hash.ComputeHash(data);
+            return Utils.HashBytesToUInt32(sum);
         }
 
         /// <summary>

ProbabilisticDataStructures/HyperLogLog.cs

@@ -208,10 +208,8 @@ public void SetHash(HashAlgorithm h)
         /// <returns>32-bit hash value</returns>
         private uint CalculateHash(byte[] data)
         {
-            var hash = new Hash(this.Hash);
-            hash.ComputeHash(data);
-            var sum = hash.Sum();
-            return Utils.ToBigEndianUInt32(sum);
+            var sum = Hash.ComputeHash(data);
+            return Utils.HashBytesToUInt32(sum);
         }
 
         /// <summary>

ProbabilisticDataStructures/InverseBloomFilter.cs

@@ -161,10 +161,8 @@ private uint Index(byte[] data)
         /// <returns>32-bit hash value</returns>
         private uint ComputeHashSum32(byte[] data)
         {
-            var hash = new Hash(this.Hash);
-            hash.ComputeHash(data);
-            var sum = hash.Sum();
-            return Utils.ToBigEndianUInt32(sum);
+            var sum = Hash.ComputeHash(data);
+            return Utils.HashBytesToUInt32(sum);
         }
 
         /// <summary>

ProbabilisticDataStructures/Utils.cs

@@ -1,6 +1,7 @@
-using System;
+using System;
 using System.Linq;
 using System.Security.Cryptography;
+using System.Text;
 
 namespace ProbabilisticDataStructures
 {
@@ -48,19 +49,32 @@ public static uint OptimalK(double fpRate)
 
         /// <summary>
         /// Returns the upper and lower base hash values from which the k hashes are
-        /// derived.
+        /// derived.  The result will be the same regardless of the endianness of the
+        /// architecture.
         /// </summary>
         /// <param name="data">The data bytes to hash.</param>
         /// <param name="algorithm">The hashing algorithm to use.</param>
         /// <returns>A HashKernel</returns>
         public static HashKernelReturnValue HashKernel(byte[] data, HashAlgorithm algorithm)
         {
-            var hash = new Hash(algorithm);
-            hash.ComputeHash(data);
-            var sum = hash.Sum();
+            var sum = algorithm.ComputeHash(data);
+            return HashKernelFromHashBytes(sum);
+        }
+
+        /// <summary>
+        /// Returns the upper and lower base hash values from which the k hashes are
+        /// derived using the given hash bytes directly.  The result will be the
+        /// same regardless of the endianness of the architecture.  Used by a unit
+        /// test to confirm the calculation is compatible with the HashKernel from
+        /// https://github.com/tylertreat/BoomFilters running in Go.
+        /// </summary>
+        /// <param name="hashBytes">The hash bytes.</param>
+        /// <returns>A HashKernel</returns>
+        public static HashKernelReturnValue HashKernelFromHashBytes(byte[] hashBytes)
+        {
             return HashKernelReturnValue.Create(
-                ToBigEndianUInt32(sum.Skip(4).Take(4).ToArray()),
-                ToBigEndianUInt32(sum.Take(4).ToArray())
+                HashBytesToUInt32(hashBytes, 0),
+                HashBytesToUInt32(hashBytes, 4)
                 );
         }
 
@@ -73,30 +87,73 @@ public static HashKernelReturnValue HashKernel(byte[] data, HashAlgorithm algori
         /// <returns>A HashKernel</returns>
         public static HashKernel128ReturnValue HashKernel128(byte[] data, HashAlgorithm algorithm)
         {
-            var hash = new Hash128(algorithm);
-            var sum = hash.ComputeHashAndSum(data);
+            var sum = algorithm.ComputeHash(data);
             return HashKernel128ReturnValue.Create(
-                ToBigEndianUInt64(sum, 8),
-                ToBigEndianUInt64(sum, 0)
+                HashBytesToUInt64(sum, 0),
+                HashBytesToUInt64(sum, 8)
                 );
         }
 
-        public static uint ToBigEndianUInt32(byte[] bytes)
+        /// <summary>
+        /// Returns the uint represented by the given hash bytes, starting at
+        /// byte <paramref name="offset"/>.  The result will be the same
+        /// regardless of the endianness of the architecture.
+        /// </summary>
+        /// <param name="hashBytes"></param>
+        /// <param name="offset"></param>
+        /// <returns></returns>
+        public static uint HashBytesToUInt32(byte[] hashBytes, int offset = 0)
         {
-            if (BitConverter.IsLittleEndian)
-                Array.Reverse(bytes);
+            return
+                ((uint)hashBytes[offset]) |
+                ((uint)hashBytes[offset + 1]) << 8 |
+                ((uint)hashBytes[offset + 2]) << 16 |
+                ((uint)hashBytes[offset + 3]) << 24;
+        }
 
-            uint i = BitConverter.ToUInt32(bytes, 0);
-            return i;
+        /// <summary>
+        /// Returns the ulong represented by the given hash bytes, starting at
+        /// byte <paramref name="offset"/>.  The result will be the same
+        /// regardless of the endianness of the architecture.
+        /// </summary>
+        /// <param name="hashBytes"></param>
+        /// <param name="offset"></param>
+        /// <returns></returns>
+        public static ulong HashBytesToUInt64(byte[] hashBytes, int offset = 0)
+        {
+            return
+                ((ulong)hashBytes[offset]) |
+                ((ulong)hashBytes[offset + 1]) << 8 |
+                ((ulong)hashBytes[offset + 2]) << 16 |
+                ((ulong)hashBytes[offset + 3]) << 24 |
+                ((ulong)hashBytes[offset + 4]) << 32 |
+                ((ulong)hashBytes[offset + 5]) << 40 |
+                ((ulong)hashBytes[offset + 6]) << 48 |
+                ((ulong)hashBytes[offset + 7]) << 56;
         }
 
-        public static ulong ToBigEndianUInt64(byte[] bytes, int offset)
+        /// <summary>
+        /// Compute the hash for the provided bytes.
+        /// </summary>
+        /// <param name="inputBytes">The bytes to hash.</param>
+        /// <returns>The hash string of the bytes.</returns>
+        public static string ComputeHashAsString(byte[] inputBytes, HashAlgorithm hashAlgorithm)
         {
-            if (BitConverter.IsLittleEndian)
-                Array.Reverse(bytes, offset, 8);
+            // Compute the hash of the input byte array.
+            byte[] data = hashAlgorithm.ComputeHash(inputBytes);
+
+            // Create a new StringBuilder to collect the bytes and create a string.
+            StringBuilder sb = new StringBuilder();
+
+            // Loop through each byte of the hashed data and format each one as a
+            // hexadecimal string.
+            for (int i = 0; i < data.Length; i++)
+            {
+                sb.Append(data[i].ToString("X2"));
+            }
 
-            ulong i = BitConverter.ToUInt64(bytes, offset);
-            return i;
+            // Return the hexadecimal string.
+            return sb.ToString();
         }
     }