Random.h - A fast single-header xorshift64 PRNG for C

Features

• Single header (you only need to download one file)
• No dependencies, standard C
• Optimized for speed
• Seeded from hardware clock

Usage

#include "Random.h"

int main(void) {
    int n   = xrandInt(0, 100);
    float f = xrandFloat(0.0f, 100.0f);
    int b   = xrandBool();
    int arr[] = {0,1,2,3};
    int choice1 = xrandChoice(arr);
    int choice2 = xrandChoiceL(arr, 4);
}

Config

Settings

• XRAND_FIXED_SEED: Fixes seed to 0xdeadbeefcafeULL
• XRAND_NO_ASSERT: Disables compile-time check that unsigned long long is 64 bit

How to use

Must be defined before the include:

#define XRAND_FIXED_SEED
#define XRAND_NO_ASSERT
#include "Random.h"

API Reference

Function	Returns	Description	Precondition
xrand()	uint64	Raw 64-bit random number	—
xrandSeed(seed)	void	Override the rng seed	—
xrandInt(min, max)	int	Random integer in [min, max]	max >= min
xrandFloat(min, max)	float	Random float in [min, max]	max >= min
xrandBool()	int	0 or 1	—
xrandChoice(arr)	element	Random element from a stack array	arr must not be a pointer
xrandChoiceL(arr, len)	element	Random element from array of known length	len > 0

Platform notes

Requires x86 for rdtsc seeding. On other platforms, define XRAND_FIXED_SEED or call xrandSeed() manually before generating numbers.

Roadmap

• Core implementation
• Cross-platform support
• XRAND_IMPLEMENTATION guard (stb-style)
• Thread safety
• C++ compatibility
• More customization options (xrandDouble, xrandShuffle, xrandWeighted, xrandString)
• Speed & quality improvements
• Benchmarks in README
• GitHub Releases with versioned header downloads

License

Licensed under the MIT License. See: https://opensource.org/licenses/MIT