big: fix ProbablyPrime bug, comments
(changes adopted from alc, agl)
R=agl1, agl
CC=golang-dev
https://golang.org/cl/181137
diff --git a/src/pkg/big/nat.go b/src/pkg/big/nat.go
index 877bc98..da9f1d7 100644
--- a/src/pkg/big/nat.go
+++ b/src/pkg/big/nat.go
@@ -596,6 +596,9 @@
// possible. n is the bit length of limit.
func randomN(z []Word, rand *rand.Rand, limit []Word, n int) []Word {
bitLengthOfMSW := uint(n % _W)
+ if bitLengthOfMSW == 0 {
+ bitLengthOfMSW = _W
+ }
mask := Word((1 << bitLengthOfMSW) - 1)
z = makeN(z, len(limit), false)
@@ -616,7 +619,7 @@
}
}
- return z
+ return normN(z)
}
@@ -702,8 +705,8 @@
var bigOne = []Word{1}
var bigTwo = []Word{2}
-// ProbablyPrime performs n Miller-Rabin tests to check whether n is prime.
-// If it returns true, n is prime with probability 1 - 1/4^n.
+// ProbablyPrime performs reps Miller-Rabin tests to check whether n is prime.
+// If it returns true, n is prime with probability 1 - 1/4^reps.
// If it returns false, n is not prime.
func probablyPrime(n []Word, reps int) bool {
if len(n) == 0 {
