Page History

...

const unsigned long mask = 0x80000000;
unsigned long x;

/* Initialize x */

x |= (x ^ mask) + 1;

This code has the desired effect for implementations where unsigned long has a precision of 32 bits but not for implementations where unsigned long has a precision of 64 bits.

...

const unsigned long mask = ~(ULONG_MAX >> 1);
unsigned long x;

/* Initialize x */

x |= (x ^ mask) + 1;

Risk Assessment

Vulnerabilities are frequently introduced while porting code. A buffer overflow vulnerability may result, for example, if an incorrectly defined integer constant is used to determine the size of a buffer. It is always best to write portable code, especially when there is no performance overhead for doing so.

...