code review 822045: math: atan2 special cases (negative zero)

math: atan2 special cases (negative zero)

Added Signbit(), revised Copysign()

[Charlie Dorian, 2010-04-08 17:55:10]

Hello rsc (cc: golang-dev@googlegroups.com),

I'd like you to review this change.

[rsc1, 2010-04-08 18:30:58]

looks good; tiny nit

http://codereview.appspot.com/822045/diff/2001/3004
File src/pkg/math/copysign.go (right):

http://codereview.appspot.com/822045/diff/2001/3004#newcode11
src/pkg/math/copysign.go:11: return
Float64frombits(Float64bits(x)&0x7fffffffffffffff |
Float64bits(y)&0x8000000000000000)
a little hard to read

const sign = 1<<63
return Float64frombits(Float64bits(x)&^sign | Float64bits(y)&sign)

http://codereview.appspot.com/822045/diff/2001/3005
File src/pkg/math/signbit.go (right):

http://codereview.appspot.com/822045/diff/2001/3005#newcode9
src/pkg/math/signbit.go:9: return Float64bits(x)&0x8000000000000000 != 0
&(1<<63)

[Charlie Dorian, 2010-04-08 20:01:42]

Hello rsc (cc: golang-dev@googlegroups.com),

Please take another look.

[Charlie Dorian, 2010-04-08 20:01:45]

Thanks for the review.

On Thu, Apr 8, 2010 at 2:30 PM,  <rsc@google.com> wrote:
> looks good; tiny nit
>
> http://codereview.appspot.com/822045/diff/2001/3004
> File src/pkg/math/copysign.go (right):
>
> http://codereview.appspot.com/822045/diff/2001/3004#newcode11
> src/pkg/math/copysign.go:11: return
> Float64frombits(Float64bits(x)&0x7fffffffffffffff |
> Float64bits(y)&0x8000000000000000)
> a little hard to read
>
> const sign = 1<<63
> return Float64frombits(Float64bits(x)&^sign | Float64bits(y)&sign)
Done.

>
> http://codereview.appspot.com/822045/diff/2001/3005
> File src/pkg/math/signbit.go (right):
>
> http://codereview.appspot.com/822045/diff/2001/3005#newcode9
> src/pkg/math/signbit.go:9: return Float64bits(x)&0x8000000000000000 != 0
> &(1<<63)
Done.

>
> http://codereview.appspot.com/822045/show
>

[rsc1, 2010-04-08 20:07:53]

LGTM

thanks

[rsc, 2010-04-08 20:24:10]

*** Submitted as http://code.google.com/p/go/source/detail?r=2d74f76a6da9 ***

math: atan2 special cases (negative zero)

Added Signbit(), revised Copysign()

R=rsc
CC=golang-dev
http://codereview.appspot.com/822045

Committer: Russ Cox <rsc@golang.org>