ref: 11b5c4b8bf0a15777e9a7f2292f6c80f5a7b4a2d dir: /sys/src/ape/lib/ap/gen/difftime.c/
#include <time.h> /* Difference in seconds between two calendar times */ double difftime(time_t t1, time_t t0) { return (double)t1-(double)t0; }