ref: 817743a2d1468248a025c4abb9fd5ff43d01e277
dir: /qw/nanosec.c/
#include <u.h>
#include <libc.h>
#include <tos.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
*/
uvlong
nanosec(void)
{
static uvlong fasthz, xstart;
uvlong x, div;
if(fasthz == ~0ULL)
return nsec() - xstart;
if(fasthz == 0){
if(_tos->cyclefreq){
fasthz = _tos->cyclefreq;
cycles(&xstart);
} else {
fasthz = ~0ULL;
xstart = nsec();
}
return 0;
}
cycles(&x);
x -= xstart;
/* this is ugly */
for(div = 1000000000ULL; x < 0x1999999999999999ULL && div > 1 ; div /= 10ULL, x *= 10ULL);
return x / (fasthz / div);
}