ref: d7613e356c55a3b7a1140a1f6d8aa6dca43b9d97 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; }