ref: 8f44d1f6e8a47395c2ebd9b6899f1b8dc94a9b3f 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; }