public void Test1()
{
const Double loadFactor = 1.0d;
// Create a unique string generator
const int KeyCount = 2_000_000;
// Derivate a minimum perfect hash function
Console.WriteLine("Generating minimum perfect hash function for {0} keys", KeyCount);
var start = DateTime.Now;
var hashFunction = new MphFunction <Int32>(Enumerable.Range(0, KeyCount), KeyCount, GetKeyBytes, loadFactor);
Console.WriteLine("Completed in {0:0.000000} s", DateTime.Now.Subtract(start).TotalMilliseconds / 1000.0);
// Show the extra hash space necessary
Console.WriteLine("Hash function map {0} keys to {1} hashes (load factor: {2:0.000000}%)",
KeyCount, hashFunction.MaxValue,
((KeyCount * 100) / (Double)hashFunction.MaxValue));
// Check for any collision
var used = new System.Collections.BitArray((Int32)hashFunction.MaxValue);
start = DateTime.Now;
for (var test = 0U; test < KeyCount; test++)
{
var hash = (Int32)hashFunction.GetHash((Int32)test, GetKeyBytes);
if (used[hash])
{
Assert.True(false, $"FAILED - Collision detected at {test}");
}
used[hash] = true;
}
var end = DateTime.Now.Subtract(start).TotalMilliseconds;
Console.WriteLine("PASS - No collision detected");
Console.WriteLine("Total scan time : {0:0.000000} s", end / 1000.0);
Console.WriteLine("Average key hash time : {0} ms", end / (Double)KeyCount);
var dic = new Dictionary <Int32, String>((Int32)KeyCount);
for (var i = 0; i < KeyCount; i++)
{
dic.Add(i, i.ToString());
}
var mphrod = new MphReadOnlyDictionary <Int32, String>(dic, GetKeyBytes, loadFactor);
for (var i = 0; i < KeyCount; i++)
{
Assert.Equal(dic[i], mphrod[i]);
}
Assert.Equal(dic.OrderBy(x => x.Key), mphrod.OrderBy(x => x.Key));
Assert.Equal(dic.Keys.OrderBy(x => x), mphrod.Keys.OrderBy(x => x));
Assert.Equal(dic.Values.OrderBy(x => x), mphrod.Values.OrderBy(x => x));
}
public void OutOfRangeKeysThatCollideOnHashFunctionFailEqualityCheck()
{
const Int32 keyCount = 2_000_000;
var dic = new Dictionary <Int32, String>(keyCount);
for (var i = 0; i < keyCount; i++)
{
dic.Add(i, i.ToString());
}
var mphrod = new MphReadOnlyDictionary <Int32, String>(dic, GetKeyBytes);
for (var i = 0; i < keyCount; i++)
{
Assert.False(mphrod.TryGetValue((i + keyCount), out var x));
}
}
