ref: d62733faff1367e247d387ca41ae27f3b6674c49
dir: /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 */ u64int nanosec(void) { static u64int fasthz, xstart; u64int 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); }