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#include <u.h>
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#include <libc.h>
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typedef uvlong u64int;
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#define TWID64	((u64int)~(u64int)0)
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u64int
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unittoull(char *s)
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{
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	char *es;
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	u64int n;
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	if(s == nil)
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		return TWID64;
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	n = strtoul(s, &es, 0);
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	if(*es == 'k' || *es == 'K'){
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		n *= 1024;
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		es++;
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	}else if(*es == 'm' || *es == 'M'){
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		n *= 1024*1024;
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		es++;
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	}else if(*es == 'g' || *es == 'G'){
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		n *= 1024*1024*1024;
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		es++;
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	}
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	if(*es != '\0')
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		return TWID64;
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	return n;
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}
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void
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main(int argc, char *argv[])
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{
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	int fd, i;
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	int n = 1000, m;
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	int s = 1;
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	double *t, t0, t1;
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	uchar *buf;
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	double a, d, max, min;
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	m = OREAD;
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	ARGBEGIN{
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	case 'n':
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		n = atoi(ARGF());
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		break;
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	case 's':
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		s = unittoull(ARGF());
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		if(s < 1 || s > 1024*1024)
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			sysfatal("bad size");
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		break;
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	case 'r':
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		m = OREAD;
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		break;
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	case 'w':
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		m = OWRITE;
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		break;
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	}ARGEND
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	fd = 0;
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	if(argc == 1){
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		fd = open(argv[0], m);
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		if(fd < 0)
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			sysfatal("could not open file: %s: %r", argv[0]);
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	}
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	buf = malloc(s);
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	t = malloc(n*sizeof(double));
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	t0 = nsec();
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	for(i=0; i<n; i++){
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		if(m == OREAD){
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			if(pread(fd, buf, s, 0) < s)
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				sysfatal("bad read: %r");
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		}else{
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			if(pwrite(fd, buf, s, 0) < s)
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				sysfatal("bad write: %r");
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		}
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		t1 = nsec();
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		t[i] = (t1 - t0)*1e-3;
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		t0 = t1;
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	}
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	a = 0.;
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	d = 0.;
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	max = 0.;
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	min = 1e12;
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	for(i=0; i<n; i++){
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		a += t[i];
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		if(max < t[i])
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			max = t[i];
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		if(min > t[i])
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			min = t[i];
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	}
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	a /= n;
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	for(i=0; i<n; i++)
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		d += (a - t[i]) * (a - t[i]);
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	d /= n;
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	d = sqrt(d);
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	print("avg = %.0fµs min = %.0fµs max = %.0fµs dev = %.0fµs\n", a, min, max, d);
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	exits(0);
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}
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