Re: Problem using static floats
Re: Problem using static floats
- Subject: Re: Problem using static floats
- From: Scott F Bayes <email@hidden>
- Date: Sat, 21 Jul 2007 20:10:29 +0900
Hi Shawn,
No, this wasn't the return value. This was on of the arguments being
received as garbage by the method parameters. Saw it while execution
was in the method. Debugger was actually pretty helpful for a change,
and the code was free-running with the same kind of symptoms (being
random-appearing, I can't guarantee it was the same problem for sure,
but the odds are on it).. If I spoke IA-32, I probably could detect
the flaw in the debugger disassembly, but 68K was my last assembly
fluency. From what I could glean, looks like doubles are passed as a
reference on the stack, whereas floats look to be passed by value on
the stack (though it could be it's an ivar reference), but am not
sure. My guess is that the 4 bytes received for the float are taken
from where the float ain't.
Best Regards
ScottB
On Jul 20, 2007, at 02:37 , Shawn Erickson wrote:
On 7/19/07, Scott F Bayes <email@hidden> wrote:
Hi Joel,
I saw something somewhat similar a few days ago and submitted a bug
report. No response yet. 10.4.10 on an original MacBook, latest
Xcode, stock standard.
In my case, passing a float into an Obj-C instance method failed.
Just before the method call, the debugger showed the expected value
in my float variable. On the other side, inside the method, the
incoming float argument was essentially a random number. When I
changed to a double, it worked fine. So did an int.
This sounds like the caller assuming the return type to be something
other then what the implementation expected. Did you get any compiler
warnings about it assuming the return type for a message?
It is highly likely that the calling code doesn't have visibility of
the methods declaration and as a result assumes the return type to be
id (a pointer) which is default return type for objective-c messages.
Pointers (integers) are passed in different registers the floats and
as a result the caller is looking in the wrong registers on return
from the method.
-Shawn
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