alessandrocuda / randq

Pseudo-Random Number Generators (PRNGs): using "quick and dirty" linear congruential method and a 64bit nonlinear generator. - C

randq.c

randq stand for "random quick": Quick Pseudo-Random Number Generators (PRNGs) Lib developed in C99.

A better way to generate a random number

PRNG (Pseudo-Random Number Generators): First, and perhaps most important: be very, very suspicious of a system-supplied rand(). System-supplied rand()s are almost always linear congruential generators that will eventually repeat itself, with a period. So, never use the built-in generators in the C and C++ languages, especially rand and srand. These have no standard implementation and are often badly flawed.

This Library provides two better way to generate a random number:

• The "suspenders-and-belt, full-body-armor, never-any-doubt" generator laying on 64bit and respect all the constraints defined in "Numerical Recipes" Third Edition at page 342. The period of the generator is 3.138*10^57.

      Developed through the following functions:
      srandq64, randq64_uint64, randq64_uint32, randq64_double;
  

• the "Quick and Dirty" Generators laying on 32bit defined in "Numerical Recipes in C" Second Edition. Use it only in very special cases, where speed is critical and if you don’t need a period longer than 2^32.

      Developed through the following functions:
      srandqd, randqd_uint32 and randq_double;
  

This generators are not designed for cryptographic use

Functions are not Thread Safe

Table of Contents

• Usage
• Testing
• Todo
• Support
• License

Usage

randq.c and randq.h should be dropped into an existing project and compiled along with it. The library provides 7 functions for generate a random number:

- Functions that use "suspenders-and-belt, full-body-armor,never-any-doubt" method:

void srandq64(uint64_t start_seed);

uint64_t randq64_uint64();

uint32_t randq64_uint32();

double randq64_double();

• void srandq64(uint64_t start_seed): Allow to initialize the starting seed for the randq library, accept a uint64_t value.

• uint64_t randq64_uint64(): Returns a unsigned long long int random value within the range [0, 2^64 - 1]

• uuint32_t randq64_uint32(): Returns a unsigned long int random value within the range [0, 2^32 - 1]

• double randq64_double(): Returns a double random value within the range [0, 1)

- Functions that use "Quick and Dirty" method:

void srandqd(uint32_t start_seed);

uint32_t randqd_uint32();

double randqd_double();

• void srandqd(uint32_t start_seed): Allow to initialize the starting seed for the randq library, accept a uint32_t value.

• uint32_t randqd_uint32(): Returns a unsigned long int random value within the range [0, 2^32 - 1]

• double randqd_double(): Returns a double random value within the range [0, 1)

- Examples

/*
 * With "suspenders-and-belt, full-body-armor, never-any-doubt" 
 * Generator - randq64_
 */

// v1 in the range 0 to 99
uint64_t v1 = randq64_uint64() % 100;                
// v2 in the range 1985-2014         
uint64_t v2 = randq64_uint32() % 100 + 1;            
// v3 in the range -1 to 1
double v3 = randq64_double()* 2.0 - 1.0;

/*
 * With Quick and Dirty Generator - randqd_
 */

// v1 in the range 0 to 99
uint32_t v4 = randqd_uint32() % 100; 
// v2 in the range 1985-2014         
uint32_t v5 = randqd_uint32() % 30 + 1985;          
// v3 in the range -1 to 1
double v6 = randqdd_double()* 2.0 - 1.0;

Testing

This repo proviedes a unit test done with CMocka and some examples.

./randq_usecase    # show some examples
./randq_utest      # unit test performed with CMocka

System requirements for building and running randq_utest.c

To build randq_utest you need CMocka as unit testing framework for C installed on your system:

MacOS with Homebrew

brew install cmocka

Linux Ubuntu/Debian

apt-get install libcmocka-dev 

BUILD

These instructions will get you a copy of randqd_utest and randqd_example up and running on your local machine for testing purposes.

git clone https://github.com/alessandrocuda/randq.git
cd randq/
make                # or 'make all'

or build just randq_utest or randq_example

make randq_utest              
make randq_example

TODO

• add Thread safe to all functions

Support

Reach out to me at one of the following places!

• Website at Alessandro Cudazzo.
• Twitter at @alessandrocuda

License

This library is free software; you can redistribute it and/or modify it under the terms of the MIT license.

• MIT license
• Copyright 2019 © Alessandro Cudazzo.