Telodendria/src/include/Rand.h

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/*
* Copyright (C) 2022-2023 Jordan Bancino <@jordan:bancino.net>
*
* Permission is hereby granted, free of charge, to any person
* obtaining a copy of this software and associated documentation files
* (the "Software"), to deal in the Software without restriction,
* including without limitation the rights to use, copy, modify, merge,
* publish, distribute, sublicense, and/or sell copies of the Software,
* and to permit persons to whom the Software is furnished to do so,
* subject to the following conditions:
*
* The above copyright notice and this permission notice shall be
* included in all copies or portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
* EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
* MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
* NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
* BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
* ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
* CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
* SOFTWARE.
*/
#ifndef TELODENDRIA_RAND_H
#define TELODENDRIA_RAND_H
/***
* @Nm Rand
* @Nd Thread-safe random numbers.
* @Dd February 16 2023
* @Xr Util
*
* .Nm
* is used for generating random numbers in a thread-safe way.
* Currently, one generator state is shared across all threads, which
* means that only one thread can generate random numbers at a time.
* This state is protected with a mutex to guarantee this behavior.
* In the future, a seed pool may be maintained to allow multiple
* threads to generate random numbers at the same time.
* .Pp
* The generator state is seeded on the first call to a function that
* needs it. The seed is determined by the current timestamp, the ID
* of the process, and the thread ID. These should all be sufficiently
* random sources, so the seed should be secure enough.
* .Pp
* .Nm
* currently uses a simple Mersenne Twister algorithm to generate
* random numbers. This algorithm was chosen because it is extremely
* popular and widespread. While it is likely not cryptographically
* secure, and does suffer some unfortunate pitfalls, this algorithm
* has stood the test of time and is simple enough to implement, so
* it was chosen over the alternatives.
* .Pp
* .Nm
* does not use any random number generator functions from the C
* standard library, since these are often flawed.
*/
#include <stddef.h>
/**
* Generate a single random integer between 0 and the passed value.
*/
extern int RandInt(unsigned int);
/**
* Generate the number of integers specified by the second argument
* storing them into the buffer pointed to in the first argument.
* Ensure that each number is between 0 and the third argument.
* .Pp
* This function allows a caller to get multiple random numbers at once
* in a more efficient manner than repeatedly calling
* .Fn RandInt ,
* since each call to these functions
* has to lock and unlock a mutex. It is therefore better to obtain
* multiple random numbers in one pass if multiple are needed.
*/
extern void RandIntN(int *, size_t, unsigned int);
#endif /* TELODENDRIA_RAND_H */