Edit report at https://bugs.php.net/bug.php?id=64142&edit=1
ID: 64142
Updated by: r...@php.net
Reported by: r...@php.net
Summary: dval to lval different behavior on ppc64
-Status: Closed
+Status: Assigned
Type: Bug
Package: *General Issues
Operating System: GNU/Linux
PHP Version: 5.4.11
Assigned To: remi
Block user comment: N
Private report: N
New Comment:
@cataphract see my latest message on php-cvs ML.
Really strange. C Test (with -O2) give the same result on x86_64 and ppc64 and
seems to prove the fix is not needed.
No I need to understand why it improves the PHP result.
I can keep the test builder for some time, so will investigate on this...
Previous Comments:
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[2013-02-05 12:37:07] cataphr...@php.net
BTW, that's with optimization turned off. If I pass -O3 to gcc , it's still
able to figure out it doesn't need to cast anything and the output is
-9223372036854775808.
In any case, we should get to the bottom of this. I very much doubt the patch
is wrong, but if we figure out the underling cause we may find out the problem
is larger.
------------------------------------------------------------------------
[2013-02-05 12:32:35] cataphr...@php.net
> (long)(double)9223372036854775807-1 = 9223372036854775807
Ah sorry, I read that wrong. It can't obviously be rounding down, because the
result seems larger; you're subtracting one here when you're adding 1 on top...
The part about the closes doubles is wrong too, they're already spaced by 1024
by then.
In any case, your explanation in the commit seems both irrelevant and wrong. AS
to the wrong part, in x86_64:
printf("%ld\n",((long)(double)9223372036854775807)+1);
double dd = 9223372036854775807;
printf("%ld\n", ((long)dd) + 1);
gives
-9223372036854775808
-9223372036854775807
So the -9223372036854775808 result is just an artifact of the compiler doing
away with the casts completely.
------------------------------------------------------------------------
[2013-02-05 11:05:02] cataphr...@php.net
The commit message says:
> On x86_64:
> (long)(double)9223372036854775807+1 = -9223372036854775808
> On ppc64
> (long)(double)9223372036854775807-1 = 9223372036854775807
How much is (long)(double)0x7fffffffffffffffL in that arch? Is it
0x7ffffffffffffffeL ?
The closest doubles near 0x7fffffffffffffff are 0x8000000000000000 and
0x7ffffffffffffffe. So basically ppp64 rounds down while x64 rounds up? If
that's the case, there's nothing to "fix" in the code; you'll presumably get
this behavior in a lot of other places, not just when casting LONG_MAX to
double.
But in any case, I don't see how that is relevant to the patch. The patch
changes a (long)dval cast to (long)(unsigned long)dval cast, which is a
double-to-long cast, not a long-to-double cast.
------------------------------------------------------------------------
[2013-02-05 07:19:18] r...@php.net
Automatic comment on behalf of remi
Revision:
http://git.php.net/?p=php-src.git;a=commit;h=6533094d9e4d0c85044a170d9fad9a3986a68675
Log: Fixed bug #64142 (dval to lval different behavior on ppc64)
------------------------------------------------------------------------
[2013-02-05 01:16:05] ras...@php.net
You should be able to commit it now
------------------------------------------------------------------------
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