🚀 go-pugleaf

In article <4cmg0s$1mb@der.twinsun.com>,
eggert@twinsun.com (Paul Eggert) wrote:
>This reminds me of a similar bug I found a long time ago when porting
>the Modula-3 runtime, which contained code that acted something like this:
>
>	int sum_overflow (int x, int y) {
>		return (x + y < x) != (y < 0);
>	}
>
>The C Standard does not guarantee that the above function works,
>since integer overflow leads to undefined behavior,
>but when I found that the function did not work with whatever old version
>of GCC I was using at the time, I reported it as a bug to the GCC maintainers
>and got a fix from them in a few days.
>
>Regardless of what the C Standard says, it should be obvious that it's
>crucial to have integer overflow checking working properly in an
>application that needs it.  

I agree, but it is possible to rewrite the function so that it doesn't
invoke undefined behavior:

  #include <limits.h>
  int sum_overflow (int x, int y) {
      return x > 0? (y > INT_MAX - x) : (y < INT_MIN - x);
  }

Thad