/// <summary>
/// Hash the given name using the given hash functions.
/// </summary>
/// <param name="name">The name to hash.</param>
/// <param name="phf1">PearsonHashFunction to use for the upper
/// eight bits of the hash.</param>
/// <param name="phf2">PearsonHashFunction to use for the lower
/// eight bits of the hash.</param>
/// <param name="hashMask">The mask value to be applied to the
/// hash.</param>
/// <returns>The hash value, masked by hashMask.</returns>
private static int HashName(string name, PearsonHashFunction phf1, PearsonHashFunction phf2, int hashMask)
{
// Get the word name as an array of uppercase ASCII bytes.
string upperName = name.ToUpperInvariant();
byte[] upperNameBytes = Encoding.ASCII.GetBytes(upperName);
// Hash the name. Use phf1 for the upper eight bits and
// phf2 for the lower eight bits. Then mask off the hash
// value to keep it within range of our hash table.
return(((phf1.Hash(upperNameBytes) << 8) | phf2.Hash(upperNameBytes)) & hashMask);
}
/// <summary>
/// Hash the given name using the given hash functions.
/// </summary>
/// <param name="name">The name to hash.</param>
/// <param name="phf1">PearsonHashFunction to use for the upper
/// eight bits of the hash.</param>
/// <param name="phf2">PearsonHashFunction to use for the lower
/// eight bits of the hash.</param>
/// <param name="hashMask">The mask value to be applied to the
/// hash.</param>
/// <returns>The hash value, masked by hashMask.</returns>
private static int HashName(string name, PearsonHashFunction phf1, PearsonHashFunction phf2, int hashMask)
{
// Get the word name as an array of uppercase ASCII bytes.
string upperName = name.ToUpperInvariant();
byte[] upperNameBytes = Encoding.ASCII.GetBytes(upperName);
// Hash the name. Use phf1 for the upper eight bits and
// phf2 for the lower eight bits. Then mask off the hash
// value to keep it within range of our hash table.
return ((phf1.Hash(upperNameBytes) << 8) | phf2.Hash(upperNameBytes)) & hashMask;
}
/// <summary>
/// Generate the MFORTH hash table.
/// </summary>
/// <param name="rom">MFORTH ROM.</param>
/// <param name="phf1">Upon return, will contain the first
/// PearsonHashFunction used by the hash table.</param>
/// <param name="phf2">Upon return, will contain the second
/// PearsonHashFunction used by the hash table.</param>
/// <returns>The MFORTH hash table.</returns>
private static CuckooHashTable<Word> GenerateHashTable(ROM rom, out PearsonHashFunction phf1, out PearsonHashFunction phf2)
{
// Initialize our random number generator.
var random = new Random(HashTableRandomSeed);
// Initialize our hash functions and the hash table.
var hashFunc1 = phf1 = new PearsonHashFunction(random);
var hashFunc2 = phf2 = new PearsonHashFunction(random);
var hashTable = new CuckooHashTable<Word>(
(w) => HashName(w.Name, hashFunc1, hashFunc2, HashMask),
(w) => HashName(w.Name, hashFunc2, hashFunc1, HashMask));
// Generate the hash table.
#if FINDING_OPTIMAL_HASH_SEED
int minValuesAtSecondLocation = int.MaxValue;
#endif
for (;;)
{
#if !FINDING_OPTIMAL_HASH_SEED
// Display a progress dot.
Console.Write(".");
#endif
// Add all of the words to our hash table; assume that
// we will be successful.
bool haveCompleteTable = true;
foreach (var word in rom.Words)
{
if (!hashTable.TryAddValue(word))
{
haveCompleteTable = false;
break;
}
}
#if !FINDING_OPTIMAL_HASH_SEED
// We're done if all of the words were added to the
// table.
if (haveCompleteTable)
{
break;
}
// We failed to generate a complete hash table; shuffle
// the hash functions, clear the table, and try again.
phf1.ShuffleAuxilliaryTable(random);
phf2.ShuffleAuxilliaryTable(random);
hashTable.Clear();
#else
// Print out the results if this seed produced better
// results than the previous best seed.
if (haveCompleteTable
&& hashTable.NumValuesStoredAtSecondHash < minValuesAtSecondLocation)
{
Console.WriteLine(
"Seed: {0}; 1st: {1}; 2nd: {2}",
HashTableRandomSeed,
hashTable.NumValuesStoredAtFirstHash,
hashTable.NumValuesStoredAtSecondHash);
minValuesAtSecondLocation = hashTable.NumValuesStoredAtSecondHash;
}
// Generate a new seed and re-create all of the hash
// functions and tables.
random = new Random(++HashTableRandomSeed);
hashFunc1 = phf1 = new PearsonHashFunction(random);
hashFunc2 = phf2 = new PearsonHashFunction(random);
hashTable = new CuckooHashTable<Word>(
(w) => HashName(w.Name, hashFunc1, hashFunc2, HashMask),
(w) => HashName(w.Name, hashFunc2, hashFunc1, HashMask));
#endif
}
// Ensure that all of the words in the ROM were added to the
// hash table.
if (rom.NumWords != hashTable.Count)
{
throw new InvalidDataException(
string.Format(
"Hash table only has {0} words; expected {1} words.",
hashTable.Count,
rom.NumWords));
}
// Return the hash table.
return hashTable;
}
/// <summary>
/// Generate the MFORTH hash table.
/// </summary>
/// <param name="rom">MFORTH ROM.</param>
/// <param name="phf1">Upon return, will contain the first
/// PearsonHashFunction used by the hash table.</param>
/// <param name="phf2">Upon return, will contain the second
/// PearsonHashFunction used by the hash table.</param>
/// <returns>The MFORTH hash table.</returns>
private static CuckooHashTable <Word> GenerateHashTable(ROM rom, out PearsonHashFunction phf1, out PearsonHashFunction phf2)
{
// Initialize our random number generator.
var random = new Random(HashTableRandomSeed);
// Initialize our hash functions and the hash table.
var hashFunc1 = phf1 = new PearsonHashFunction(random);
var hashFunc2 = phf2 = new PearsonHashFunction(random);
var hashTable = new CuckooHashTable <Word>(
(w) => HashName(w.Name, hashFunc1, hashFunc2, HashMask),
(w) => HashName(w.Name, hashFunc2, hashFunc1, HashMask));
// Generate the hash table.
#if FINDING_OPTIMAL_HASH_SEED
int minValuesAtSecondLocation = int.MaxValue;
#endif
for (;;)
{
#if !FINDING_OPTIMAL_HASH_SEED
// Display a progress dot.
Console.Write(".");
#endif
// Add all of the words to our hash table; assume that
// we will be successful.
bool haveCompleteTable = true;
foreach (var word in rom.Words)
{
if (!hashTable.TryAddValue(word))
{
haveCompleteTable = false;
break;
}
}
#if !FINDING_OPTIMAL_HASH_SEED
// We're done if all of the words were added to the
// table.
if (haveCompleteTable)
{
break;
}
// We failed to generate a complete hash table; shuffle
// the hash functions, clear the table, and try again.
phf1.ShuffleAuxilliaryTable(random);
phf2.ShuffleAuxilliaryTable(random);
hashTable.Clear();
#else
// Print out the results if this seed produced better
// results than the previous best seed.
if (haveCompleteTable &&
hashTable.NumValuesStoredAtSecondHash < minValuesAtSecondLocation)
{
Console.WriteLine(
"Seed: {0}; 1st: {1}; 2nd: {2}",
HashTableRandomSeed,
hashTable.NumValuesStoredAtFirstHash,
hashTable.NumValuesStoredAtSecondHash);
minValuesAtSecondLocation = hashTable.NumValuesStoredAtSecondHash;
}
// Generate a new seed and re-create all of the hash
// functions and tables.
random = new Random(++HashTableRandomSeed);
hashFunc1 = phf1 = new PearsonHashFunction(random);
hashFunc2 = phf2 = new PearsonHashFunction(random);
hashTable = new CuckooHashTable <Word>(
(w) => HashName(w.Name, hashFunc1, hashFunc2, HashMask),
(w) => HashName(w.Name, hashFunc2, hashFunc1, HashMask));
#endif
}
// Ensure that all of the words in the ROM were added to the
// hash table.
if (rom.NumWords != hashTable.Count)
{
throw new InvalidDataException(
string.Format(
"Hash table only has {0} words; expected {1} words.",
hashTable.Count,
rom.NumWords));
}
// Return the hash table.
return(hashTable);
}
