Edit report at http://bugs.php.net/bug.php?id=47168&edit=1
ID: 47168
Updated by: il...@php.net
Reported by: exploringbinary at gmail dot com
Summary: printf of floating point variable prints maximum of
40 decimal places
-Status: Assigned
+Status: Closed
Type: Bug
Package: Math related
Operating System: *
PHP Version: 5.2.9
Assigned To: iliaa
Block user comment: N
Private report: N
New Comment:
This bug has been fixed in SVN.
Snapshots of the sources are packaged every three hours; this change
will be in the next snapshot. You can grab the snapshot at
http://snaps.php.net/.
Thank you for the report, and for helping us make PHP better.
Previous Comments:
------------------------------------------------------------------------
[2010-11-19 17:36:12] il...@php.net
Automatic comment from SVN on behalf of iliaa
Revision: http://svn.php.net/viewvc/?view=revision&revision=305561
Log: Fixed bug #47168 (printf of floating point variable prints maximum
of 40 decimal places).
------------------------------------------------------------------------
[2009-04-30 14:44:43] exploringbinary at gmail dot com
A reader of my blog pointed out that serialize and unserialize have
similar issues. I ran some tests and discovered that 2^-143 is the
smallest negative power of two that PHP can serialize, and 2^-40 is the
smallest it can unserialize.
Here's are the testcases:
This code works it prints
d:8.9683101716788292539118693330554632401936764280097009392452370
16894662929189507849514484405517578125E-44;
<?php
//Serialize 2^-143
$dyadic = //Compute as (2^-50)^2 * 2^-43 to break up
0.00000000000000088817841970012523233890533447265625*
0.00000000000000088817841970012523233890533447265625*
0.0000000000001136868377216160297393798828125;
echo serialize ($dyadic);
?>
This code fails it prints
d:4.4841550858394146269559346665277316200968382140048504696226185
08447331464594753924757242202758789062E-44;
<?php
//Serialize 2^-144
$dyadic = //Compute as (2^-50)^2 * 2^-44 to break up
0.00000000000000088817841970012523233890533447265625*
0.00000000000000088817841970012523233890533447265625*
0.00000000000005684341886080801486968994140625;
echo serialize ($dyadic);
?>
This code works it prints
0.0000000000009094947017729282379150390625
<?php
//Serialize and unserialize 2^-40
$dyadic = 0.0000000000009094947017729282379150390625;
printf ("%1.40f",unserialize(serialize($dyadic)));
?>
This code fails it prints
Fails, prints 0.0000000000004547473508864641189575195312
<?php
//Serialize and unserialize 2^-41
$dyadic = 0.00000000000045474735088646411895751953125;
printf ("%1.41f",unserialize(serialize($dyadic)));
?>
------------------------------------------------------------------------
[2009-04-30 03:48:24] ras...@php.net
There are a couple of other places that need to be changed. I have a
patch but I haven't had a chance to go through and fix the test cases
yet. I'll get to it before RC2 next week.
------------------------------------------------------------------------
[2009-04-30 01:23:58] ivan dot rey at inpltda dot com
I agree also.
Full precision should be available for the developer.
I wonder if recompiling php with a different CAP in In
php-5.2.8\ext\standard\formatted_print.c I found this:
#define MAX_FLOAT_PRECISION 40 is the actual solution or if it has some
further implications.
------------------------------------------------------------------------
[2009-04-29 05:21:05] ras...@php.net
I agree with Rick here. The 40-digit limit is strangely arbitrary and
doesn't match the size of the double. We are hiding available precision
here.
------------------------------------------------------------------------
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the rest of the comments, please view the bug report online at
http://bugs.php.net/bug.php?id=47168
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