code review 119630043: cmd/link: fix zig-zag decoding

cmd/link: fix zig-zag decoding

The >>1 shift needs to happen before converting to int32, otherwise
large values will decode with an incorrect sign bit.

The <<31 shift can happen before or after, but before is consistent
with liblink and the go12symtab doc.

Bug demo at http://play.golang.org/p/jLrhPUakIu

[mdempsky, 2014-08-09 00:00:32]

Hello golang-codereviews@googlegroups.com,

I'd like you to review this change to
https://code.google.com/p/go

[minux, 2014-08-09 00:35:26]

test?

[rsc, 2014-08-11 17:51:08]

LGTM

I have some tests for this pending, although it's unlikely we'd get to a
delta that large.

[rsc, 2014-08-11 18:14:40]

*** Submitted as https://code.google.com/p/go/source/detail?r=62969513e59e ***

cmd/link: fix zig-zag decoding

The >>1 shift needs to happen before converting to int32, otherwise
large values will decode with an incorrect sign bit.

The <<31 shift can happen before or after, but before is consistent
with liblink and the go12symtab doc.

Bug demo at http://play.golang.org/p/jLrhPUakIu

LGTM=rsc
R=golang-codereviews, minux, rsc
CC=golang-codereviews
https://codereview.appspot.com/119630043

Committer: Russ Cox <rsc@golang.org>