math/big: fix big.Exp and document better
- always return 1 for y <= 0
- document that the sign of m is ignored
- protect against div-0 panics by treating
m == 0 the same way as m == nil
- added extra tests
Fixes #4239.
R=agl, remyoudompheng, agl
CC=golang-dev
https://golang.org/cl/6724046
diff --git a/src/pkg/math/big/int_test.go b/src/pkg/math/big/int_test.go
index 27834ce..d3c5a0e 100644
--- a/src/pkg/math/big/int_test.go
+++ b/src/pkg/math/big/int_test.go
@@ -767,8 +767,10 @@
x, y, m string
out string
}{
+ {"5", "-7", "", "1"},
+ {"-5", "-7", "", "1"},
{"5", "0", "", "1"},
- {"-5", "0", "", "-1"},
+ {"-5", "0", "", "1"},
{"5", "1", "", "5"},
{"-5", "1", "", "-5"},
{"-2", "3", "2", "0"},
@@ -779,6 +781,7 @@
{"0x8000000000000000", "3", "6719", "5447"},
{"0x8000000000000000", "1000", "6719", "1603"},
{"0x8000000000000000", "1000000", "6719", "3199"},
+ {"0x8000000000000000", "-1000000", "6719", "1"},
{
"2938462938472983472983659726349017249287491026512746239764525612965293865296239471239874193284792387498274256129746192347",
"298472983472983471903246121093472394872319615612417471234712061",
@@ -807,12 +810,22 @@
continue
}
- z := y.Exp(x, y, m)
- if !isNormalized(z) {
- t.Errorf("#%d: %v is not normalized", i, *z)
+ z1 := new(Int).Exp(x, y, m)
+ if !isNormalized(z1) {
+ t.Errorf("#%d: %v is not normalized", i, *z1)
}
- if z.Cmp(out) != 0 {
- t.Errorf("#%d: got %s want %s", i, z, out)
+ if z1.Cmp(out) != 0 {
+ t.Errorf("#%d: got %s want %s", i, z1, out)
+ }
+
+ if m == nil {
+ // the result should be the same as for m == 0;
+ // specifically, there should be no div-zero panic
+ m = &Int{abs: nat{}} // m != nil && len(m.abs) == 0
+ z2 := new(Int).Exp(x, y, m)
+ if z2.Cmp(z1) != 0 {
+ t.Errorf("#%d: got %s want %s", i, z1, z2)
+ }
}
}
}
