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Posted to user@thrift.apache.org by Daniel Eggert <da...@umzugsagenten.de> on 2012/03/28 11:53:05 UTC

C strict aliasing rules

The Cocoa code has this in TBinaryProtocol:


- (void) writeDouble: (double) value
{
  // spit out IEEE 754 bits - FIXME - will this get us in trouble on
  // PowerPC?
  [self writeI64: *((int64_t *) &value)];
}

this should be changed to

- (void) writeDouble: (double) value
{
    // spit out IEEE 754 bits - FIXME - will this get us in trouble on
    // PowerPC?
    union {
        int64_t i64;
        double d;
    } u;
    u.d = value;
    [self writeI64: u.i64];
}

since the current code violates C strict aliasing rules -- it works but it's undefined behavior.

C.f. <http://labs.qt.nokia.com/2011/06/10/type-punning-and-strict-aliasing/>


Daniel

Re: C strict aliasing rules

Posted by Jake Farrell <jf...@apache.org>.

If you would like to contribute a patch for this please see
http://thrift.apache.org/docs/HowToContribute/




On Wednesday, March 28, 2012, Richard Salz wrote:

> Is Cocoa C?
>
> --
> STSM, WebSphere Appliance Architect
> https://www.ibm.com/developerworks/mydeveloperworks/blogs/soma/
>
>

Re: C strict aliasing rules

Posted by Richard Salz <rs...@us.ibm.com>.

Is Cocoa C?

--
STSM, WebSphere Appliance Architect
https://www.ibm.com/developerworks/mydeveloperworks/blogs/soma/