🚀 go-pugleaf

As I reported earlier the following little program, when compiled with
gcc 2.3.1 gives a bad answer when run on Interactive Unix 2.2.  It
works when compiled with gcc 2.1.  I can now also report that it works
(even when compiled with gcc 2.3.1) when run on a machine with a FPU.
That is to say the problem is caused by a bug in Interactive's 80387
emulator that is used when no physical 80387 is present.  (Or is it
ATT's emulator?   In other words will the problem affect non ISC
system V.3.2's on 386's ?  How about System V.4 ?

The program:

------------------------------------------------

#include <stdio.h>


void Store (float a, float *b) { *b=a; }
float Sum (float a, float b) {float r; Store(a+b, &r); return (r); }
float Diff (float a, float b){float r; Store(a-b, &r); return (r); }
float Mul (float a, float b) {float r; Store(a*b, &r); return (r); }


int main () {
	volatile int digits = 0;
	volatile float b = 1.0;
	volatile float base = 2;

	do {
		digits++;
		b = Mul (b, base);
	}
	while (Diff (Diff (Sum (b, 1.0), b), 1.0) == 0.0);

	printf ("Digits = %d\n", digits);

	return 0;
}

--
John Hughes, RCI CalvaCom, Paris, France