/* timeit — run a command once and print its elapsed wall time in µs.
 *
 * The benchmark harness races fastwc against several wc implementations.
 * Timing both sides by wrapping the command in `date +%s%N` forks added
 * over a millisecond of noise per sample — more than the whole run on a
 * small case — so every sub-millisecond race was decided by fork jitter,
 * not by speed. This helper measures a plain fork + exec + wait with
 * clock_gettime and prints the elapsed microseconds on its own stdout.
 * The timed command's output is discarded, exactly as the old date
 * wrapper did, so capture_count (which runs the command directly) is the
 * only path that sees real output.
 *
 * usage: timeit <cmd> [arg...]
 */
#define _POSIX_C_SOURCE 200809L

#include <fcntl.h>
#include <stdio.h>
#include <sys/wait.h>
#include <time.h>
#include <unistd.h>

int main(int argc, char **argv)
{
    struct timespec t0, t1;
    pid_t pid;
    int nullfd;

    if (argc < 2)
        return 2;

    clock_gettime(CLOCK_MONOTONIC, &t0);

    pid = fork();
    if (pid < 0)
        return 2;
    if (pid == 0)
    {
        /* child: run the timed command with its output thrown away */
        nullfd = open("/dev/null", O_WRONLY);
        if (nullfd >= 0)
        {
            dup2(nullfd, STDOUT_FILENO);
            dup2(nullfd, STDERR_FILENO);
            close(nullfd);
        }
        execvp(argv[1], &argv[1]);
        _exit(127);
    }

    if (waitpid(pid, NULL, 0) < 0)
        return 2;
    clock_gettime(CLOCK_MONOTONIC, &t1);

    printf("%lld\n",
           ((long long)(t1.tv_sec - t0.tv_sec) * 1000000000LL
            + (t1.tv_nsec - t0.tv_nsec)) / 1000);
    return 0;
}