long long atoll(const char *p)
{
	long long n;
	int c, neg = 0;
	unsigned char   *up = (unsigned char *)p;

	if (!isdigit(c = *up)) {
		while (isspace(c))
			c = *++up;
		switch (c) {
		case '-':
			neg++;
			/* FALLTHROUGH */
		case '+':
			c = *++up;
		}
		if (!isdigit(c))
			return (0);
	}

	for (n = '0' - c; isdigit(c = *++up); ) {
		n *= 10; /* two steps to avoid unnecessary overflow */
		n += '0' - c; /* accum neg to avoid surprises at MAX */
	}

	return (neg ? n : -n);
}