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#include <u.h>
#include <libc.h>
/*
* nsec() is wallclock and can be adjusted by timesync
* so need to use cycles() instead, but fall back to
* nsec() in case we can't
*
* "fasthz" is how many ticks there are in a second
* can be read from /dev/time
*/
uvlong
nanosec(void)
{
static uvlong fasthz, xstart;
uvlong x, div;
int f, n, i;
char tmp[128], *e;
if(fasthz == ~0ULL)
return nsec() - xstart;
if(fasthz == 0){
fasthz = ~0ULL;
xstart = nsec();
if((f = open("/dev/time", OREAD)) >= 0 && (n = read(f, tmp, sizeof(tmp)-1)) > 2){
tmp[n] = 0;
e = tmp;
for(i = 0; i < 3; i++)
strtoll(e, &e, 10);
if((fasthz = strtoll(e, nil, 10)) < 1)
fasthz = ~0ULL;
else
cycles(&xstart);
}
close(f);
if(fasthz == ~0ULL){
fprint(2, "couldn't get fasthz, falling back to nsec()\n");
fprint(2, "you might want to disable aux/timesync\n");
return 0;
}
}
cycles(&x);
x -= xstart;
/* this is ugly */
for(div = 1000000000ULL; x < 0x1999999999999999ULL && div > 1 ; div /= 10ULL, x *= 10ULL);
return x / (fasthz / div);
}
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