Skip to content

Instantly share code, notes, and snippets.

@louisswarren
Created Oct 26, 2021
Embed
What would you like to do?
Roll dice for a while in C
#include <stdio.h>
#include <stdlib.h>
#include <time.h>
unsigned long long counts[6] = {0};
unsigned long long trials = 0;
void
roll_dice(void)
{
/* Does not check for overflows. If you think you're going to do more
* than ULLONG_MAX trials, it's your responsibility to check! */
int rmax = RAND_MAX >> 3;
int r = rand();
do {
counts[r & 7] += !((r & 6) == 6);
trials += !((r & 6) == 6);
r >>= 3;
rmax >>= 3;
} while (rmax);
}
void
print_table(void)
{
int i;
printf("%llu trials:\n", trials);
for (i = 0; i < 6; ++i) {
printf("%d: %llu (%0.4f)\n",
i, counts[i], (float) counts[i] / trials);
}
}
void
trial_time(int runtime)
{
int trials_per_grain;
int i;
unsigned long long start_trials = trials;
clock_t start_clock = clock();
/* Run initially for 10ms, then approximate time target time at 10ms
* granularity. This is much faster than checking the clock every
* iteration. */
while (clock() - start_clock < CLOCKS_PER_SEC / 100)
roll_dice();
trials_per_grain = trials - start_trials;
while (clock() - start_clock < CLOCKS_PER_SEC * runtime) {
for (i = 0; i < trials_per_grain; ++i)
roll_dice();
}
}
int
main(void)
{
trial_time(1);
print_table();
}
Sign up for free to join this conversation on GitHub. Already have an account? Sign in to comment