SIZE_MAX could be defined as -1 promoted to an unsigned type, meaning that the unsigned comparison would always yield false. Or am I missing something?

In any case, if the promotion is what is intended, 'nbytes' should be probably replaced with '(size_t) nbytes' to silence the warning and to make it explicit.

Am So., 4. Apr. 2021 um 08:24 Uhr schrieb Jeffrey Walton <noloader@gmail.com>:

On Sun, Apr 4, 2021 at 2:17 AM Marc Nieper-Wißkirchen
<marc.nieper+gnu@gmail.com> wrote:
>
> GCC prints the following warning when compiling the new code:
>
> lib/xmalloc.c: In function 'xpalloc':
> lib/xmalloc.c:132:64: warning: comparison of integer expressions of different signedness: 'long unsigned int' and 'idx_t' {aka 'long int'} [-Wsign-compare]
> 132 | = ((INT_MULTIPLY_WRAPV (n, item_size, &nbytes) || SIZE_MAX < nbytes)
>
> If I understand the error message correctly, it is because 'nbytes' is a signed type while SIZE_MAX is unsigned.
>
> Does the comparison make any sense, by the way?

Only for positive integers.

If idx_t is negative, like -1, then -1 will be promoted to an unsigned
type and then -1 > 0.

Jeff