static int hex(char c)
{
	char lc = tolower(c);

	if (isdigit(lc))
		return lc - '0';
	if (isxdigit(lc))
		return lc - 'a' + 10;
	return -1;
}

This weakness involves numeric computation errors, such as integer overflows, underflows, or precision losses, which can lead to miscalculations and exploitable behaviors in software.