How to multiply two ints and check

[robison at m.cs.uiuc.edu]

Re: "How to multiply two ints and check"

There is a much simpler, faster, and machine-independent way to check
for multiplication overflow --- check the product by division.  To wit:

	int vmul(n1,n2,p_ovf)
		int n1,n2;
		int *p_ovf;
		{
			int product = n1*n2;
			if( n2!=0 && product/n2 != n1 )
				*p_ovf = YES;
			else
				*p_ovf = NO;
			return product;
		}

This code doesn't need to know sizeof(int), and even works on decimal machines!

Arch D. Robison
University of Illinois at Urbana-Champaign

UUCP: {pur-ee,convex}!uiucdcs!robison
Internet: robison at CS.UIUC.EDU