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phf.net's Introduction

Phf.Net

NuGet Build Status License

Tiny perfect hash library for dotnet. This is an implementation of the CHD algorithm

Installation

This project is available as a NuGet package

Example

Some code

var strings = Enumerable.Range(0, 6).Select(x => $"str{x}").ToArray();
var settings = new PhfSettings {ItemsPerBucket = 4, Alpha = 80, Seed = 31337, NoDivision = true};
var hashFunction = PerfectHashFunction.Create(strings, settings);
foreach (var str in strings)
    Console.WriteLine($"{str} - {hashFunction.Evaluate(str)}");

Output

str0 - 0
str1 - 4
str2 - 6
str3 - 3
str4 - 2
str5 - 5

Hints

  • You can serialize created PerfectHashFunction for the future usage
  • PhfSettings has default values for all properties

phf.net's People

Contributors

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Forkers

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phf.net's Issues

Low bits per key

As I understand the CHD Algorithm it is suppose to be space-efficient for the MPHF replacement size, however the DisplacementMap seems to always be n bytes (4n bits) where n is the number of keys, shouldn't it be closer to 2 bits per key?

For example 65536 (2^16) keys become 2^16/4 unsigned integers which is 65536 bytes. How should the DisplacementMap be saved?

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