openssl/bugs/dggccbug.c

/* NOCW */
/* dggccbug.c */
/* bug found by Eric Young (eay@cryptsoft.com) - May 1995 */

#include <stdio.h>

/*
 * There is a bug in gcc version 2.5.8 (88open OCS/BCS, DG-2.5.8.3, Oct 14
 * 1994) as shipped with DGUX 5.4R3.10 that can be bypassed by defining
 * DG_GCC_BUG in my code. The bug manifests itself by the vaule of a pointer
 * that is used only by reference, not having it's value change when it is
 * used to check for exiting the loop.  Probably caused by there being 2
 * copies of the valiable, one in a register and one being an address that is
 * passed.
 */

/*-
 * compare the out put from
 * gcc dggccbug.c; ./a.out
 * and
 * gcc -O dggccbug.c; ./a.out
 * compile with -DFIXBUG to remove the bug when optimising.
 */

void inc(a)
int *a;
{
    (*a)++;
}

main()
{
    int p = 0;
#ifdef FIXBUG
    int dummy;
#endif

    while (p < 3) {
        fprintf(stderr, "%08X\n", p);
        inc(&p);
#ifdef FIXBUG
        dummy += p;
#endif
    }
}