Edit report at http://bugs.php.net/bug.php?id=53045&edit=1
ID: 53045
Updated by: rasmus@php.net
Reported by: remy at wh dot nl
Summary: broken result of intval()
Status: Open
Type: Bug
Package: *Math Functions
Operating System: FreeBSD
PHP Version: 5.2.14
Block user comment: N
New Comment:
Not sure there is a whole lot we can do about this. It is a typical
IEEE-754
precision problem. Try this simple C program, for example:
[a.c]
#include <stdio.h>
#include <math.h>
int main(int argc, char *argv[]) {
printf("%.16f\n",log(8) / log(2));
}
LDFLAGS=-lm make a
./a
I get: 3.0000000000000000
I bet you get 2.9999999999999996
or something along those lines.
We might be able to do something clever with PHP's precision setting
internally
and round to that precision before doing the truncation there, but in
reality
you are dealing with floating point numbers here and whenever you deal
with
floating point numbers when programming you have to treat them as
approximations, never as exact values. Unless you are using arbitrary
precision
functions such as the gmp or bcmath function (which are orders of
magnitude
slower) you are going to have to account for these imprecisions in your
code.
Previous Comments:
------------------------------------------------------------------------
[2010-10-13 08:38:16] remy at wh dot nl
php -i output:
phpinfo()
PHP Version => 5.2.14
System => FreeBSD xxx.xxx.com 7.3-STABLE FreeBSD 7.3-STABLE #7: Thu Jul
15 20:09:49 CEST 2010 remy@xxx.xxx.com:/usr/obj/usr/src/sys/XXX
i386
Build Date => Sep 22 2010 20:07:20
Configure Command => './configure' '--with-libxml-dir=/usr/local/lib'
'--with-config-file-path=/home/www/php' '--with-zlib' '--with-mysql'
'--with-pgsql' '--enable-calendar' '--enable-mbstring'
'--with-apxs2=/home/www/bin/apxs' '--enable-ftp' '--with-gd'
'--enable-mbregex' '--enable-gd-native-ttf'
'--with-png-dir=/usr/local/lib' '--with-jpeg-dir=/usr/local/lib'
'--with-xpm-dir=/usr/X11R6/lib' '--with-freetype-dir=/usr/local/lib'
'--with-iconv' '--with-curl' '--with-bz2'
------------------------------------------------------------------------
[2010-10-13 08:33:34] remy at wh dot nl
var_dump( unpack("H*",pack("d", 3.0000)) );
var_dump( unpack("H*",pack("d", log(8,2))) );
array(1) {
[1]=>
string(16) "0000000000000840"
}
array(1) {
[1]=>
string(16) "ffffffffffff0740"
}
------------------------------------------------------------------------
[2010-10-13 05:25:02] cataphract@php.net
I can't reproduce on mipsel/32-bit/Linux, PHP 5.2.14.
Can you show us the result of this:
<?php
var_dump( unpack("H*",pack("d", 3.0000)) );
var_dump( unpack("H*",pack("d", log(8,2))) );
I get
array(1) {
[1]=>
string(16) "0000000000000840"
}
array(1) {
[1]=>
string(16) "0000000000000840"
}
------------------------------------------------------------------------
[2010-10-12 19:33:45] remy at wh dot nl
CPU: Intel(R) Pentium(R) 4 CPU 3.20GHz (3211.39-MHz 686-class CPU)
Origin = "GenuineIntel" Id = 0xf43 Family = f Model = 4 Stepping =
3
Features=0xbfebfbff<FPU,VME,DE,PSE,TSC,MSR,PAE,MCE,CX8,APIC,SEP,MTRR,PGE,MCA,CMOV,PAT,PSE36,CLFLUSH,DT
S,ACPI,MMX,FXSR,SSE,SSE2,SS,HTT,TM,PBE>
Features2=0x649d<SSE3,DTES64,MON,DS_CPL,EST,CNXT-ID,CX16,xTPR>
AMD Features=0x20000000<LM>
Logical CPUs per core: 2
------------------------------------------------------------------------
[2010-10-12 19:30:32] remy at wh dot nl
Yes, 32bit, here is some hardware and OS info from sysctl:
kern.ostype: FreeBSD
kern.osrelease: 7.3-STABLE
kern.osrevision: 199506
kern.version: FreeBSD 7.3-STABLE #7: Thu Jul 15 20:09:49 CEST 2010
kern.maxvnodes: 100000
kern.maxproc: 6164
kern.maxfiles: 12328
kern.argmax: 262144
kern.securelevel: -1
kern.clockrate: { hz = 1000, tick = 1000, profhz = 2000, stathz = 133 }
kern.posix1version: 200112
kern.ngroups: 16
kern.job_control: 1
kern.saved_ids: 0
kern.boottime: { sec = 1281862574, usec = 963320 } Sun Aug 15 10:56:14
2010
kern.domainname:
kern.osreldate: 703100
kern.bootfile: /boot/kernel/kernel
kern.maxfilesperproc: 11095
kern.maxprocperuid: 5547
hw.machine: i386
hw.model: Intel(R) Pentium(R) 4 CPU 3.20GHz
hw.ncpu: 2
hw.byteorder: 1234
hw.physmem: 2134020096
hw.usermem: 1906421760
hw.pagesize: 4096
hw.floatingpoint: 1
hw.machine_arch: i386
hw.realmem: 2147155968
------------------------------------------------------------------------
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