rand provides a minimal pseudo-random number generator (PRNG) without any libc dependency. It uses a linear congruential algorithm with a fixed multiplier and increment — the same approach used by many C standard library implementations.
Functions
srand_custom
void srand_custom(unsigned int new_seed);
12345. Call this before the first rand_custom() if a different starting sequence is needed.
There is no hardware entropy source on this bare-metal OS. If you need different sequences across boots, seed with a value derived from observable state (e.g. a timer counter read immediately before enabling IRQs).
rand_custom
unsigned int rand_custom(void);
seed = seed × 1103515245 + 12345
return (seed / 65536) % 32768
[0, 32767], matching the range of rand() in a standard C library.
unsigned int r = rand_custom(); // 0 <= r <= 32767
Implementation
static unsigned int seed = 12345;
void srand_custom(unsigned int new_seed) {
seed = new_seed;
}
unsigned int rand_custom(void) {
seed = seed * 1103515245 + 12345;
return (seed / 65536) % 32768;
}
The LCG parameters produce a period of 2³² iterations before the sequence repeats. The output passes basic statistical tests but is not cryptographically secure. Do not use it for security-sensitive purposes.
Usage example
#include "rand.h"
srand_custom(1);
for (int i = 0; i < 5; i++) {
unsigned int r = rand_custom();
PRINT("%d\n", (int)r);
}