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To: <internals@lists.php.net>,
	"Iain Lewis" <ilewis@uk.ibm.com>
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Date: Wed, 4 Feb 2009 11:30:53 -0600
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Subject: Re: [PHP-DEV] casting doubles to ints
From: php_lists@realplain.com ("Matt Wilmas")

Hi Iain,

(Yes, this subject has me sending a message to the list again instead of
lurking, and I should be back with some internals stuff again soon, hehe.
:^))

----- Original Message -----
From: "Iain Lewis"
Sent: Wednesday, February 04, 2009
Subject: [PHP-DEV] casting doubles to ints

> Hello all,
>
> I wanted to suggest back porting the behaviour of the DVAL_TO_LVAL macro
> from zend_operators.h from 5.3 to 5.2, and wondered whether people
> thought this was a good idea or not?
>
> The reason I want to do this is that while writing some tests, I noticed
> that the behaviour of casting a float to an int is a bit
> counter-intuitive on 64bit platforms for PHP 5.2. It looks as though
> this has been fixed in 5.3, and it would seem like a good idea to put
> this change back to 5.2 as well. From a personal point of view, it would
> mean I could write one test that would work on both 5.2 and 5.3, but it
> also seems like a sensible change, as the current behaviour is
> non-obvious. The change would cause some current tests to break, but I
> am happy to do the work to fix those up.

NOOOO, please. :-)  In fact, I thought maybe your message was complaining
about the 5.3 changes.  I was suggesting reverting 5.3 to 5.2's behavior at
the very least -- see my "DVAL_TO_LVAL() change, different behavior" thread
[1] from last year for the reasons.  It breaks long-time behavior
(overflow-wise), and isn't even consistent with how it works.  I was
thinking there will be some breakage, bug reports, etc. as 5.3 is used more,
if others are doing stuff like my examples showed. *shrug*

In addition to my suggestion of going back to the behavior of 5.2 and
earlier, I think DVAL_TO_LVAL() can be updated to ensure consistent,
reliable overflow behavior on all systems -- it seems like it has been on
the majority, but a simple (long) cast of the double (when out of range) in
C is implementation-defined, so depending...  Anyway, I didn't get to test
my idea yet, but will get to it soon!

The thing that I think was originally trying to be fixed (large function
args) can be done easily in zend_parse_parameters() for those desired use
cases.

[1] http://marc.info/?t=120799728700001&r=1&w=2

> This is how a few expressions get evaluated at the moment. Changing the
> macro would make the 5.2 behaviour match 5.3
>
> Expression 5.3 (RHEL5-64)       5.2 (RHEL5-64)
>
> (int) (PHP_INT_MAX) 9223372036854775807  9223372036854775807
> (int) (PHP_INT_MAX + 1) 9223372036854775807 -9223372036854775808
> (int) (PHP_INT_MAX + 1000) 9223372036854775807 -9223372036854775808
> (int) (PHP_INT_MAX + 10000) 9223372036854775807 -9223372036854765568
>
> Does this seem like a good change?


- Matt