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"Hardening" the bad prand

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Imbus 2025-08-28 14:44:44 +02:00
parent d0aa85f62e
commit f3522129a3
1 changed files with 22 additions and 10 deletions
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32
prand.c
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@ -2,14 +2,13 @@
#include <stdint.h>
#include <stdio.h>
#include <time.h>
#include <unistd.h>
#define BUILD_SEED \
#define PRAND_BUILD_SEED \
((uint64_t)(__TIME__[0]) * (uint64_t)(__TIME__[1]) * (uint64_t)(__TIME__[3]) * (uint64_t)(__TIME__[4]) * \
(uint64_t)(__TIME__[6]) * (uint64_t)(__TIME__[7]))
#define PRNG_SAVE_INTERVAL 50 // Save every 1000 calls to prand()
static uint64_t seed = BUILD_SEED;
static uint64_t seed = PRAND_BUILD_SEED * 6364136223846793005ULL + 1;
uint64_t prand() {
seed = seed * 6364136223846793005ULL + 1;
@ -17,31 +16,44 @@ uint64_t prand() {
}
inline uint64_t prand_range(uint64_t min, uint64_t max) {
return min + (prand() % (max - min + 1));
uint64_t range = max - min + 1;
uint64_t x;
uint64_t limit = UINT64_MAX - (UINT64_MAX % range);
do {
x = prand();
} while (x > limit);
return min + (x % range);
}
void sprand(uint64_t s) {
if (s) {
seed = s;
seed ^= (s * 0x9e3779b97f4a7c15ULL) + (seed << 6) + (seed >> 2);
} else {
rand_reseed();
seed ^= PRAND_BUILD_SEED;
}
}
void rand_reseed() {
seed = BUILD_SEED;
}
#undef PRAND_BUILD_SEED
#define PRAND_MAIN
#ifdef PRAND_MAIN
int main() {
// time(NULL) provides a somewhat unique seed at runtime
sprand(time(NULL));
sprand(getpid());
sprand(0);
uint64_t rn1 = prand();
uint64_t rn2 = prand();
printf("rn1 = %lu\n", rn1);
printf("rn2 = %lu\n", rn2);
for (int i = 0; i < 40; i++) {
uint64_t random = prand_range(0, 1000);
printf("random = %lu\n", random);
}
}
#endif