/* runt: run a command N times, report min/median/max wall time and median
 * mean user/sys CPU of the child, in milliseconds.  C89 for xlc on AIX 4.3.3.
 * Usage: runt N [-q] cmd [args...]   (-q: send the child's stdout to /dev/null)
 * Claude Opus 5.5, 2026-10-09. */
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <fcntl.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/time.h>
#include <sys/resource.h>
#include <sys/wait.h>

static double tv_ms(struct timeval *a, struct timeval *b)
{
	return (b->tv_sec - a->tv_sec) * 1000.0 + (b->tv_usec - a->tv_usec) / 1000.0;
}

static int cmp(const void *a, const void *b)
{
	double x = *(const double *)a, y = *(const double *)b;
	return (x < y) ? -1 : (x > y);
}

int main(int argc, char **argv)
{
	int n, i, quiet = 0, argi = 2;
	double *wall, *usr, *sys;
	struct timeval t0, t1;
	struct rusage r0, r1;
	pid_t pid;
	int status;

	if (argc < 3) { fprintf(stderr, "usage: runt N [-q] cmd [args]\n"); return 2; }
	n = atoi(argv[1]);
	if (strcmp(argv[2], "-q") == 0) { quiet = 1; argi = 3; }
	wall = (double *)malloc(n * sizeof(double));
	usr  = (double *)malloc(n * sizeof(double));
	sys  = (double *)malloc(n * sizeof(double));
	for (i = 0; i < n; i++) {
		getrusage(RUSAGE_CHILDREN, &r0);
		gettimeofday(&t0, NULL);
		pid = fork();
		if (pid == 0) {
			if (quiet) {
				int fd = open("/dev/null", O_WRONLY);
				dup2(fd, 1);
			}
			execvp(argv[argi], argv + argi);
			_exit(127);
		}
		waitpid(pid, &status, 0);
		gettimeofday(&t1, NULL);
		getrusage(RUSAGE_CHILDREN, &r1);
		wall[i] = tv_ms(&t0, &t1);
		usr[i] = tv_ms(&r0.ru_utime, &r1.ru_utime);
		sys[i] = tv_ms(&r0.ru_stime, &r1.ru_stime);
	}
	qsort(wall, n, sizeof(double), cmp);
	/* AIX charges CPU in 10 ms ticks, so per-run CPU is useless; report means */
	{
		double su = 0, ss = 0;
		for (i = 0; i < n; i++) { su += usr[i]; ss += sys[i]; }
		printf("n=%d wall min %.2f med %.2f max %.2f  cpu mean usr %.2f sys %.2f  (ms)\n",
		    n, wall[0], wall[n / 2], wall[n - 1], su / n, ss / n);
	}
	return 0;
}