math/big: (*Rat).SetString("1/0") should not be ok

[gopherbot]

by casey.marshall:

Issue in 1.3 & tip.

Calling big.Rat.SetString with a rational string value that has a zero denominator will
produce an incorrect and unexpected result.

big.Rat.SetString simply assumes the denominator is 1 when it is actually 0.

big.Rat.SetString with a zero denominator should return nil, false.

http://play.golang.org/p/kTfKTZd8JI

-Casey

[minux]

Comment 1:

I think we should detect this special case in (*Rat).SetString as if b is zero,
(*Rat).norm() will treat it as an integer with value a.

Labels changed: added release-go1.4maybe, repo-main.

Status changed to Accepted.

[gopherbot]

Comment 3 by casey.marshall:

Proposed a fix: https://golang.org/cl/159760043/

[minux]

Comment 4:

Add "Fixes issue #8920" to your CL description, and run "hg mail 159760043", otherwise we
can't see it.

[gopherbot]

Comment 5:

CL https://golang.org/cl/159760043 mentions this issue.

[griesemer]

Comment 6:

Fixed with r=0ca77a6b76c1a990f7c01ba84381bc95ae8cbc81.

Status changed to Fixed.