ref: 8e9d2434e97fe6cf4b0d3e7f43e3e35d7ae1033f dir: /sys/src/cmd/1l/cputime.c/
double cputime(void) { long t[4]; long times(long*); int i; times(t); for(i=1; i<4; i++) t[0] += t[i]; return t[0] / 100.; }