math: pure go version of math.Sqrt is broken

If you pass math.Float64frombits(uint64(2)) to math.Sqrt on a machine that uses the software version (such as ppc64x https://golang.org/src/math/stubs_ppc64x.s#L87) it will end up in an infinite loop here https://golang.org/src/math/sqrt.go#L110

Unfortunatelly i don't have a ppc64x machine nearby. So I can't test this properly, however I did copy the library and manually call math.sqrt (the unexported, pure go version) with the argument and I have reproduced the problem.

[cespare]

Nice find, any subnormal with 0 LSB will hit this. Fixed in https://golang.org/cl/16158.

[gopherbot]

CL https://golang.org/cl/16158 mentions this issue.

[binarycrusader]

Should this fix also be applied to src/runtime/sqrt.go#L120 ?

https://github.com/golang/go/blob/master/src/runtime/sqrt.go#L120

[cespare]

@binarycrusader yeah, I'll submit another CL

[gopherbot]

CL https://golang.org/cl/16291 mentions this issue.