ref: 41fb60c4bc05b9e85c2e4495e15a9b17ba3e8ada 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; }