Strange comparision in hash_SHA2_template.c/add_length

[Marcin Stępnicki]

Hi,

We have the following function:

/* adds *inc* to the length of the hash_state *hs*
 * return 1 on success
 * return 0 if the length overflows
 */
static int add_length(hash_state *hs, sha2_word_t inc) {
    sha2_word_t overflow_detector;
    overflow_detector = hs->length_lower;
    hs->length_lower += inc;
    if (overflow_detector > hs->length_lower) {
        overflow_detector = hs->length_upper;
        hs->length_upper++;
        if (hs->length_upper > hs->length_upper)
            return 0;
    }
    return 1;
}

Can you tell me when the condition which returns 0 is met? I may be missing something really obvious, but it seems to me that we should compare length_upper with overflow_detector instead.

Thank you,
Marcin