#include <limits.h>
#include <errno.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

/*
 * Decode decimal integer from 'str'; the value is written in '*v'.
 * Returned value is a pointer to the next non-decimal character in the
 * string. If there is no digit at all, or the value encoding is not
 * minimal (extra leading zeros), or the value does not fit in an
 * 'unsigned long', then NULL is returned.
 */
static const char *
decode_decimal_pornin(const char *str, unsigned long *v)
{
	const char *orig;
	unsigned long acc;

	orig = str;
	acc = 0;
	for (orig = str;; str ++) {
		int c;

		c = *str;
		if (c < '0' || c > '9') {
			break;
		}
		c -= '0';
		if (acc > (ULONG_MAX / 10)) {
			return NULL;
		}
		acc *= 10;
		if ((unsigned long)c > (ULONG_MAX - acc)) {
			return NULL;
		}
		acc += (unsigned long)c;
	}
	if (str == orig || (*orig == '0' && str != (orig + 1))) {
		return NULL;
	}
	*v = acc;
	return str;
}

static const char *
decode_decimal_solar(const char *str, unsigned long *v)
{
	char *end;

	errno = 0;
	*v = strtoul(str, &end, 10);
	if (errno ||
	    str == end ||
	    end - str != strspn(str, "0123456789") ||
	    (*v == 0 && end - str != 1))
		return NULL;
	return end;
}

static void test_simple(const char *str)
{
	unsigned long vp = 1111111111U, vs = 2222222222U;
	const char *pp, *ps;

	pp = decode_decimal_pornin(str, &vp);
	ps = decode_decimal_solar(str, &vs);

	if (pp != ps || (pp && vp != vs))
		printf("%s: %p != %p || %lu != %lu\n",
		    str, pp, ps, vp, vs);
}

static void test_tree(const char *str, int level)
{
	char buf[100];

	test_simple(str);

	if (++level > 2)
		return;

	snprintf(buf, sizeof(buf), "-%s", str);
	test_tree(buf, level);

	snprintf(buf, sizeof(buf), "x%s", str);
	test_tree(buf, level);

	snprintf(buf, sizeof(buf), " %s", str);
	test_tree(buf, level);

	snprintf(buf, sizeof(buf), "\n%s", str);
	test_tree(buf, level);

	snprintf(buf, sizeof(buf), "%s%s", str, str);
	test_tree(buf, level);

	snprintf(buf, sizeof(buf), "%sx%s", str, str);
	test_tree(buf, level);

	snprintf(buf, sizeof(buf), "%s %s", str, str);
	test_tree(buf, level);

	snprintf(buf, sizeof(buf), "%s\n%s", str, str);
	test_tree(buf, level);
}

static void test(const char *str)
{
	test_tree(str, 0);
}

int main(void)
{
	test("");
	test("0");
	test("00");
	test("12345678");
	test("2147483647");
	test("2147483648");
	test("4294967295");
	test("4294967296");
	test("4294967297");
	test("9999999999");
	test("99999999999999999999");
	test("999999999999999999999999999999");

	return 0;
}