add: print

src/interval.c

@@ -0,0 +1,11 @@
+#include <bits/types/struct_timeval.h>
+
+double interval_to_ms(struct timeval const *t)
+{
+    return (double)t->tv_sec * 1000.0 + (double)t->tv_usec / 1000.0;
+}
+
+double get_interval(struct timeval const *start, struct timeval const *stop)
+{
+    return interval_to_ms(stop) - interval_to_ms(start);
+}