wyhash-dotnet

Zero-allocation C# implementation of Wang Yi's 64-bit wyhash hash algorithm and wyrand PRNG.

wyhash is an extremely fast, portable hashing algorithm, and passes all of the SMHasher tests (which evaluates collision, dispersion and randomness qualities of hash functions).

Note wyhash-dotnet currently implements wyhash v1. v2 will be implemented once considered "stable".

Getting Started

Install the WyHash package from NuGet:

Install-Package WyHash

WyHash implements HashAlgorithm, so can be integrated into existing projects easily:

var seed = 42;
var hasher = WyHash64.Create(seed);

var result = hasher.ComputeHash(myData);

A common use case is getting the resulting hash as a 64-bit unsigned integer (ulong), so a static convenience method is also provided:

// Note that if no seed is specified, it default to 0
var seed = 42;
var result = WyHash64.ComputeHash64(myData, seed);

The wyrand PRNG is also implemented:

var rng = new WyRng(42);

// Generate pseudorandom values
ulong a64BitVal = rng.NextLong();
uint a32BitVal = rng.Next();

// Fill a buffer with pseudorandom bytes
var buffer = new byte[256];
rng.NextBytes(buffer);

// Span is also supported
Span<byte> spanBuffer = stackalloc byte[128];
rng.NextBytes(spanBuffer);

Performance & Future Work

Note wyhash-dotnet currently implements wyhash v1. v2 will be implemented once considered "stable".

Future improvements include support for Span and incremental hashing (useful for hashing streams).

At present (July 2019), wyhash is the fastest algorithm in the SMHasher benchmark.

On a dev laptop with 64GB RAM and an Intel Xeon CPU E3-1545M v5 2.90GHz CPU, this implementation can process data at a rate of around 5.5GB/s on .NET Core 3, or 3.3GB/s on .NET Core 2 or the .NET Framework - this is very fast.

The reason for the performance improvement on .NET Core 3 is that it supports hardware intrinsics, and wyhash-dotnet uses the BMI2 MULX instruction to achieve faster 64-bit integer multiplication (on systems where BMI2 is available). Support for intrinsics won't make it into the .NET Framework, but will also be in the newly announced .NET 5.

Note that PInvokeing into a native DLL built using the reference C code (see the WyHash.Native project) achieves around 10.8GB/s (more or less RAM SPEED), so there is still work to do to bridge the performance gap between C# and native - I'm very much open to suggestions here!

Latest benchmarks (DataSize is the size of data hashed, in bytes):

BenchmarkDotNet=v0.11.5, OS=Windows 7 SP1 (6.1.7601.0)
Intel Xeon CPU E3-1545M v5 2.90GHz, 1 CPU, 8 logical and 4 physical cores
Frequency=2836064 Hz, Resolution=352.6014 ns, Timer=TSC
.NET Core SDK=3.0.100-preview4-011223
  [Host] : .NET Core 3.0.0-preview4-27615-11 (CoreCLR 4.6.27615.73, CoreFX 4.700.19.21213), 64bit RyuJIT
  Core   : .NET Core 3.0.0-preview4-27615-11 (CoreCLR 4.6.27615.73, CoreFX 4.700.19.21213), 64bit RyuJIT

Job=Core  Runtime=Core

Method	DataSize	Mean	Error	StdDev	Min	Max	Ratio	RatioSD	Rank	Gen 0	Gen 1	Gen 2	Allocated
TestXxHash	100	20.84 ns	0.4168 ns	0.6964 ns	20.02 ns	22.99 ns	0.95	0.03	2	-	-	-	-
TestXxHashNative	100	24.33 ns	0.3217 ns	0.3009 ns	23.99 ns	24.92 ns	1.10	0.02	4	-	-	-	-
TestWyHashNative	100	18.63 ns	0.1110 ns	0.0984 ns	18.47 ns	18.87 ns	0.84	0.01	1	-	-	-	-
TestWyHash	100	22.18 ns	0.2429 ns	0.2273 ns	21.84 ns	22.52 ns	1.00	0.00	3	-	-	-	-

TestXxHash	1024	106.06 ns	1.0322 ns	0.9150 ns	105.25 ns	108.04 ns	0.79	0.01	3	-	-	-	-
TestXxHashNative	1024	93.75 ns	1.9055 ns	2.1943 ns	91.79 ns	99.02 ns	0.71	0.02	2	-	-	-	-
TestWyHashNative	1024	75.38 ns	1.1722 ns	0.9788 ns	74.37 ns	77.46 ns	0.56	0.01	1	-	-	-	-
TestWyHash	1024	133.58 ns	2.0582 ns	1.9252 ns	131.38 ns	137.66 ns	1.00	0.00	4	-	-	-	-

rzer/wyhash-dotnet

wyhash-dotnet

Getting Started

Performance & Future Work