github.com/afumu/libc@v0.0.6/musl/src/time/__month_to_secs.c

int __month_to_secs(int month, int is_leap)
{
	static const int secs_through_month[] = {
		0, 31*86400, 59*86400, 90*86400,
		120*86400, 151*86400, 181*86400, 212*86400,
		243*86400, 273*86400, 304*86400, 334*86400 };
	int t = secs_through_month[month];
	if (is_leap && month >= 2) t+=86400;
	return t;
}