Pastable version of Writing characters to stdout at a specified rate

<pre class='prettyprint' language='c'>#include &lt;math.h&gt;
#include &lt;stdio.h&gt;
#include &lt;stdlib.h&gt;
#include &lt;time.h&gt;
#include &lt;unistd.h&gt;

int
sleeptill(const struct timespec *when)
{
    struct timespec now, diff;

clock_gettime(CLOCK_REALTIME, &amp;now);
    diff.tv_sec = when-&gt;tv_sec - now.tv_sec;
    diff.tv_nsec = when-&gt;tv_nsec - now.tv_nsec;
    while (diff.tv_nsec &lt; 0) {
        diff.tv_nsec += 1000000000;
        --diff.tv_sec;
    }
    if (diff.tv_sec &lt; 0)
        return 0;
    return nanosleep(&amp;diff, 0);
}

int
main(int argc, char **argv)
{
    double rate = 0.0;
    char *endp;
    struct timespec start;
    double offset;

if (argc &gt;= 2) {
        rate = strtod(argv[1], &amp;endp);
        if (endp == argv[1] || *endp)
            rate = 0.0;
        else
            rate = 1 / rate;

if (!argv[2])
            argv[2] = &quot;.&quot;;
    }

if (!rate) {
        fprintf(stderr, &quot;usage: %s rate [char]\n&quot;, argv[0]);
        return 1;
    }

clock_gettime(CLOCK_REALTIME, &amp;start);
    offset = start.tv_nsec / 1000000000.0;

while (1) {
        struct timespec till = start;
        double frac;
        double whole;

frac = modf(offset += rate, &amp;whole);
        till.tv_sec += whole;
        till.tv_nsec = frac * 1000000000.0;
        sleeptill(&amp;till);
        write(STDOUT_FILENO, argv[2], 1);
    }
}</pre>
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Pastable version of Writing characters to stdout at a specified rate