ref: b64a7e5eaa4815f7ab35d6545a3fbc080e2c7519 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; }