Hi all,
Since noticing and reporting last year [1] different behavior when casting
out-of-range doubles to int after the DVAL_TO_LVAL() macro was updated, I've
wondered how to get the behavior I observed, and thought could be relied on
(that was wrong to think, since it was un- or implementation-defined), back.
And how to do so (what should be expected?), while keeping in mind the
reason for the change: consistent behavior for tests. [2] Except that the
current code does not give consistent results, depending on which
DVAL_TO_LVAL definition is used on a platform. [3]
[1] http://marc.info/?l=php-internals&m=120799720922202&w=2
[2] http://marc.info/?l=php-internals&m=123495655802226&w=2
[3] http://marc.info/?l=php-internals&m=123496364812725&w=2
So after I finally started to test my ideas for "consistent/reliable
overflow across platforms" a few days ago, I noticed that my workaround
technique quit working (0 instead of overflow) with doubles over 2^63,
without resorting to fmod(). That's on Windows, but I suspect the same may
happen on other systems that are limited to 64-bit integer processing
internally or something (32-bit platforms?). On 64-bit Linux anyway, it
looks like doubles > 2^63 do rollover as expected (128-bit "internal
processing?"): http://marc.info/?l=php-internals&m=123376495021789&w=2
I wasn't sure how to rethink things after that... But of course with
doubles, precision has been lost long before 2^63 anyway, as far as
increments of 1 (it's 1024 at 2^63).
What I wound up with for now, is using 5.2's method on 64-bit platforms, and
on 32-bit, overflow behavior should be reliable up to 2^63 on platforms that
have zend_long64 type available (long long, __int64), which I'm guessing is
most (?), because of the unsigned long involvement. Finally a fallback
workaround for 32-bit platforms without a 64-bit type.
I updated a few other places in the code where only a (long) cast was used.
And sort of unrelated, but I added an 'L' conversion specifier for
zend_parse_parameters() in case it would be useful for PHP functions that
want to limit values to LONG_MAX/LONG_MIN, without overflow, which I thought
the DVAL_TO_LVAL change was *trying* to do.
http://realplain.com/php/dval_to_lval.diff
http://realplain.com/php/dval_to_lval_5_3.diff
And here is an initial version of zend_dval_to_lval() (before 2^63 issue and
thinking of zend_long64 + unsigned long), where some configure checks would
set ZEND_DVAL_TO_LVAL_USE_* as needed.
http://realplain.com/php/dval_to_lval.txt
Any general feedback, comments, questions, suggestions? Hoping these
conversion issues could be sorted out for good in a "nice," logical way. :-)
Unfortunately on Windows, I'm just guessing, rather than testing, conversion
results in different environments...
Thanks,
Matt
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