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	cem
	Nov 20 2019, 8:40 PM

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	#define _BSD_VISIBILE
	#include <sys/param.h>
	#include <sys/time.h>
	#include <err.h>
	#include <assert.h>
	#include <stdio.h>
	#include <time.h>

	static inline int64_t
	mynow(void)
	{
	int x;
	struct timespec tp;

	x = clock_gettime(CLOCK_VIRTUAL, &tp);
	assert(x == 0);

	return (tstosbt(tp));
	}

	int
	main(int argc, char **argv)
	{
	size_t iterations = 1, i;
	int64_t a, b, t;
	size_t sz;
	unsigned sec, usec;

	for (t = 0; t < mstosbt(100); iterations *= 2) {
	a = mynow();
	for (i = 0; i < iterations; i++) {
	int retry = 10;
	unsigned long rndval;

	__asm __volatile(
	"1:\n\t"
	"rdrand %1\n\t"
	"jc 2f\n\t"
	"dec %0\n\t"
	"jne 1b\n\t"
	"2:"
	: "+r" (retry), "=r" (rndval) : : "cc");
	if (retry == 0)
	errx(1, "failed 10 times");
	}
	b = mynow();
	t = b - a;
	}

	sz = sizeof(unsigned long);
	sec = t >> 32;
	usec = sbttous(t & 0xffffffff);

	printf("%zu iterations of %zu bytes each took %u.%06u seconds.ms, or\n",
	iterations, sz, sec, usec);

	double x = (double)sz * iterations / (sec + (((double)usec) / 1000000));
	printf("%.3f B/s %.3f kB/s %.3f MiB/s\n", x, x/1024, x/1024/1024);
	}