ref: b566c02d19b2e6321bb7e2090188feb0ed1e0c0a
dir: /sys/src/libc/port/muldiv.c/
#include <u.h>
#include <libc.h>
ulong
umuldiv(ulong a, ulong b, ulong c)
{
	return ((uvlong)a * (uvlong)b) / c;
}
long
muldiv(long a, long b, long c)
{
	int s;
	long v;
	s = 0;
	if(a < 0) {
		s = !s;
		a = -a;
	}
	if(b < 0) {
		s = !s;
		b = -b;
	}
	if(c < 0) {
		s = !s;
		c = -c;
	}
	v = umuldiv(a, b, c);
	if(s)
		v = -v;
	return v;
}