big: fix carry error, add test case.

crypto/x509: reenable tests.

R=gri
CC=go-dev
http://go/go-review/1026004

src/pkg/big/arith.go

@@ -82,9 +82,6 @@ func mulWW_g(x, y Word) (z1, z0 Word) {
 		// z = z[1]*_B + z[0] = x*y
 		z0 = t1<<_W2 + t0;
 		z1 = (t1 + t0>>_W2)>>_W2;
-		if z0 < t0 {
-			z1++;
-		}
 		return;
 	}
 

src/pkg/big/arith_test.go

@@ -278,10 +278,11 @@ type mulWWTest struct {
 
 var mulWWTests = []mulWWTest{
 	mulWWTest{_M, _M, _M-1, 1},
+	// 32 bit only: mulWWTest{0xc47dfa8c, 50911, 0x98a4, 0x998587f4},
 }
 
 
-func TestMulWWW(t *testing.T) {
+func TestMulWW(t *testing.T) {
 	for i, test := range mulWWTests {
 		q, r := mulWW_g(test.x, test.y);
 		if q != test.q || r != test.r {

src/pkg/big/int_test.go

@@ -263,11 +263,40 @@ func checkDiv(x, y []byte) bool {
 }
 
 
+type divTest struct {
+	x, y string;
+	q, r string;
+}
+
+
+var divTests = []divTest{
+	divTest{
+		"476217953993950760840509444250624797097991362735329973741718102894495832294430498335824897858659711275234906400899559094370964723884706254265559534144986498357",
+		"9353930466774385905609975137998169297361893554149986716853295022578535724979483772383667534691121982974895531435241089241440253066816724367338287092081996",
+		"50911",
+		"1",
+	},
+}
+
+
 func TestDiv(t *testing.T) {
 	err := quick.Check(checkDiv, nil);
 	if err != nil {
 		t.Error(err);
 	}
+
+	for i, test := range divTests {
+		x, _ := new(Int).SetString(test.x, 10);
+		y, _ := new(Int).SetString(test.y, 10);
+		expectedQ, _ := new(Int).SetString(test.q, 10);
+		expectedR, _ := new(Int).SetString(test.r, 10);
+
+		q, r := new(Int).Div(x, y);
+
+		if CmpInt(q, expectedQ) != 0 || CmpInt(r, expectedR) != 0 {
+			t.Errorf("#%d got (%s, %s) want (%s, %s)", i, q, r, expectedQ, expectedR);
+		}
+	}
 }
 
 

src/pkg/crypto/x509/x509_test.go

@@ -4,17 +4,6 @@
 
 package x509
 
-import "testing"
-
-func TestToKeepGoTestHappy(t *testing.T) {
-}
-
-/*
-
-Div is broken for this key in 32-bit mode.
-
-TODO(agl): reenabled when Div is fixed.
-
 import (
 	"big";
 	"crypto/rsa";
@@ -61,5 +50,3 @@ var rsaPrivateKey = &rsa.PrivateKey{
 	P: bigFromString("98920366548084643601728869055592650835572950932266967461790948584315647051443"),
 	Q: bigFromString("94560208308847015747498523884063394671606671904944666360068158221458669711639"),
 }
-
-*/
\ No newline at end of file