big: fix large division.
I missed a case.
R=rsc, agl
CC=golang-dev
https://golang.org/cl/156092
diff --git a/src/pkg/big/nat.go b/src/pkg/big/nat.go
index 8fabd7c..7fad9f8 100644
--- a/src/pkg/big/nat.go
+++ b/src/pkg/big/nat.go
@@ -310,20 +310,26 @@
// D2.
for j := m; j >= 0; j-- {
// D3.
- qhat, rhat := divWW_g(u[j+n], u[j+n-1], v[n-1]);
+ var qhat Word;
+ if u[j+n] == v[n-1] {
+ qhat = _B - 1
+ } else {
+ var rhat Word;
+ qhat, rhat = divWW_g(u[j+n], u[j+n-1], v[n-1]);
- // x1 | x2 = q̂v_{n-2}
- x1, x2 := mulWW_g(qhat, v[n-2]);
- // test if q̂v_{n-2} > br̂ + u_{j+n-2}
- for greaterThan(x1, x2, rhat, u[j+n-2]) {
- qhat--;
- prevRhat := rhat;
- rhat += v[n-1];
- // v[n-1] >= 0, so this tests for overflow.
- if rhat < prevRhat {
- break
+ // x1 | x2 = q̂v_{n-2}
+ x1, x2 := mulWW_g(qhat, v[n-2]);
+ // test if q̂v_{n-2} > br̂ + u_{j+n-2}
+ for greaterThan(x1, x2, rhat, u[j+n-2]) {
+ qhat--;
+ prevRhat := rhat;
+ rhat += v[n-1];
+ // v[n-1] >= 0, so this tests for overflow.
+ if rhat < prevRhat {
+ break
+ }
+ x1, x2 = mulWW_g(qhat, v[n-2]);
}
- x1, x2 = mulWW_g(qhat, v[n-2]);
}
// D4.
