Hi Matt,
I tried to look into this issue once again, but I completely
misunderstand why do we need all this magic. Why do we need conversion
of positive double into negative long?
I would stay with single DVAL_TO_LVAL() definition and use it in places
instead of (long)Z_DVAL().
#define DVAL_TO_LVAL(d, l) \
if ((d) > LONG_MAX) { \
(l) = LONG_MAX; \
} else if ((d) < LONG_MIN) { \
(l) = LONG_MIN; \
} else {\
(l) = (long) (d); \
}
Or may be we need a second macro for conversion into unsigned long where
it needed?
#define DVAL_TO_ULONG(d, l) \
if ((d) > ULONG_MAX) { \
(l) = ULONG_MAX; \
} else if ((d) < 0) { \
(l) = 0; \
} else {\
(l) = (unsigned long) (d); \
}
It also possible to add notices in case of overflow detection.
Thanks. Dmitry.
Matt Wilmas wrote:
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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