// Copyright 2009 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

package main

import Big "bignum"

const (
	sa = "991";
	sb = "2432902008176640000";  // 20!
	sc = "93326215443944152681699238856266700490715968264381621468592963895217599993229915608941463976156518286253697920827223758251185210916864000000000000000000000000";  // 100!
)


var (
	a = Big.NatFromString(sa, 10);
	b = Big.NatFromString(sb, 10);
	c = Big.NatFromString(sc, 10);
)


var test_msg string;
func TEST(n uint, b bool) {
	if !b {
		panic("TEST failed: ", test_msg, "(", n, ")\n");
	}
}


func TEST_EQ(n uint, x, y *Big.Natural) {
	if x.Cmp(y) != 0 {
		println("TEST failed:", test_msg, "(", n, ")\n");
		println("x =", x.String(10));
		println("y =", y.String(10));
		panic();
	}
}


func TestConv() {
	test_msg = "TestConv";
	TEST(0, a.Cmp(Big.Nat(991)) == 0);
	TEST(1, b.Cmp(Big.Fact(20)) == 0);
	TEST(2, c.Cmp(Big.Fact(100)) == 0);
	TEST(3, a.String(10) == sa);
	TEST(4, b.String(10) == sb);
	TEST(5, c.String(10) == sc);
}


func TestShift() {
	test_msg = "TestShift1L";
	TEST(0, b.Shl(0).Cmp(b) == 0);
	TEST(1, c.Shl(1).Cmp(c) > 0);
	
	test_msg = "TestShift1R";
	TEST(0, b.Shr(0).Cmp(b) == 0);
	TEST(1, c.Shr(1).Cmp(c) < 0);

	test_msg = "TestShift2";
	for i := uint(0); i < 100; i++ {
		TEST(i, c.Shl(i).Shr(i).Cmp(c) == 0);
	}

	test_msg = "TestShift3L";
	{	const m = 3;
		p := b;
		f := Big.Nat(1<<m);
		for i := uint(0); i < 100; i++ {
			TEST_EQ(i, b.Shl(i*m), p);
			p = p.Mul(f);
		}
	}

	test_msg = "TestShift3R";
	{	p := c;
		for i := uint(0); c.Cmp(Big.NatZero) == 0; i++ {
			TEST_EQ(i, c.Shr(i), p);
			p = p.Shr(1);
		}
	}
}


func TestMul() {
	test_msg = "TestMulA";
	TEST_EQ(0, b.Mul(Big.MulRange(0, 100)), Big.Nat(0));
	TEST_EQ(0, b.Mul(Big.MulRange(21, 100)), c);
	
	test_msg = "TestMulB";
	const n = 100;
	p := b.Mul(c).Shl(n);
	for i := uint(0); i < n; i++ {
		TEST_EQ(i, b.Shl(i).Mul(c.Shl(n-i)), p);
	}
}


func TestDiv() {
	test_msg = "TestDivA";
	TEST_EQ(0, c.Div(Big.Nat(1)), c);
	TEST_EQ(1, c.Div(Big.Nat(100)), Big.Fact(99));
	TEST_EQ(2, b.Div(c), Big.Nat(0));
	TEST_EQ(4, Big.Nat(1).Shl(100).Div(Big.Nat(1).Shl(90)), Big.Nat(1).Shl(10));
	TEST_EQ(5, c.Div(b), Big.MulRange(21, 100));
	
	test_msg = "TestDivB";
	const n = 100;
	p := Big.Fact(n);
	for i := uint(0); i < n; i++ {
		TEST_EQ(i, p.Div(Big.MulRange(1, uint64(i))), Big.MulRange(uint64(i+1), n));
	}
}


func TestMod() {
	test_msg = "TestModA";
	for i := uint(0); ; i++ {
		d := Big.Nat(1).Shl(i);
		if d.Cmp(c) < 0 {
			TEST_EQ(i, c.Add(d).Mod(c), d);
		} else {
			TEST_EQ(i, c.Add(d).Div(c), Big.Nat(2));
			TEST_EQ(i, c.Add(d).Mod(c), d.Sub(c));
			break;
		}
	}
}


func main() {
	TestConv();
	TestShift();
	TestMul();
	TestDiv();
	TestMod();
	print("PASSED\n");
}