aam@hcrvx1.UUCP (Allen McIntosh) (10/18/84)
The System 5.2 C compiler for the VAX contains a bug "fix" for the infamous
"i *= 0.5" bug discussed recently on the net. Alas, the fix introduces
yet another bug. To demonstrate it, try running the following C program:
int a[2] = { 2, 9 };
main()
{
int i;
i = 0;
a[i++] *= 0.5;
printf("i = %d, a[0] = %d, a[1] = %d\n", i, a[0], a[1]);
if( i != 1 || a[0] != 1 || a[2] != 9 )
printf("Wrong. Correct answer is i=1, a[0]=1, a[1]=9\n");
}
On our VAX running System 5.2, the output looks like this:
i = 2, a[0] = 2, a[1] = 1
Wrong. Correct answer is i=1, a[0]=1, a[1]=9
The problem is the routine assign() added to local.c to fix the original
problem. It blindly makes a copy of the left subtree of the "*=" without
checking for side effects.
Does anyone have a working fix for this that does not degrade code quality?