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and subject line Bug#294386: Arithetical bug in perl?
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From: "Rafal Ramocki" <[EMAIL PROTECTED]>
To: [EMAIL PROTECTED]
Subject: Arithetical bug in perl?
Date: Wed, 9 Feb 2005 17:53:16 +0330
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Package: perl
Version: 5.6.1-8.8, v5.8.4-5
I was writing a small script, but happened something wired.
This is my script:
-----
#!/usr/bin/perl
my $z1=1;
my $z2=1;
while ($z2 < 3 )
{
$z1 = $z1 + 0.01;
if ($z1 > 7.11)
{
$z1 = 0.01;
$z2 = $z2 + 0.01;
print "z2= $z2\n";
}
}
-----
after I ran it i saw on the console folowing output (fragment)
<cut>
z2= 2.23
z2= 2.24
z2= 2.25
z2= 2.26
z2= 2.27
z2= 2.27999999999999
z2= 2.28999999999999
z2= 2.29999999999999
z2= 2.30999999999999
<cut>
z2= 2.70999999999999
z2= 2.71999999999999
z2= 2.72999999999999
z2= 2.73999999999999
z2= 2.74999999999998
z2= 2.75999999999998
z2= 2.76999999999998
z2= 2.77999999999998
<cut>
I have wondering about that for some time. I don't have idea what is
happening and way. In the middle of operation from z2 is substractet that
verry small value 0.00000000000001 or added 0.00999999999999 insteed of 0.01.
and I dont know why.
I've tested that script on 3 folowing machines:
Debian stable
Kernel 2.4.27
libc6 2.2.5-11.8
zeus:~# cat /proc/cpuinfo
processor : 0
vendor_id : GenuineIntel
cpu family : 6
model : 5
model name : Pentium II (Deschutes)
stepping : 2
cpu MHz : 233.866
cache size : 512 KB
fdiv_bug : no
hlt_bug : no
f00f_bug : no
coma_bug : no
fpu : yes
fpu_exception : yes
cpuid level : 2
wp : yes
flags : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca
cmov pat pse36 mmx fxsr
bogomips : 466.94
Debian Testing:
libc6 2.3.2.ds1-20
kernel 2.4.28
cerber:/home/interblock/maniac# cat /proc/cpuinfo
processor : 0
vendor_id : GenuineIntel
cpu family : 15
model : 2
model name : Intel(R) Celeron(R) CPU 2.00GHz
stepping : 9
cpu MHz : 1995.042
cache size : 128 KB
fdiv_bug : no
hlt_bug : no
f00f_bug : no
coma_bug : no
fpu : yes
fpu_exception : yes
cpuid level : 2
wp : yes
flags : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca
cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe cid
bogomips : 3984.58
Debian Testing
libc6 2.3.2.ds1-20
kernel 2.4.29
hermes:/home/staff/maniac# cat /proc/cpuinfo
processor : 0
vendor_id : GenuineIntel
cpu family : 6
model : 8
model name : Celeron (Coppermine)
stepping : 3
cpu MHz : 567.975
cache size : 128 KB
fdiv_bug : no
hlt_bug : no
f00f_bug : no
coma_bug : no
fpu : yes
fpu_exception : yes
cpuid level : 2
wp : yes
flags : fpu vme de pse tsc msr pae mce cx8 sep mtrr pge mca cmov
pat pse36 mmx fxsr sse
bogomips : 1130.49
If i can give you any other help please ask.
---------------------------------------
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From: Florian Weimer <[EMAIL PROTECTED]>
To: "Rafal Ramocki" <[EMAIL PROTECTED]>
Cc: [EMAIL PROTECTED]
Subject: Re: Bug#294386: Arithetical bug in perl?
References: <[EMAIL PROTECTED]>
Date: Wed, 09 Feb 2005 20:39:36 +0100
In-Reply-To: <[EMAIL PROTECTED]> (Rafal Ramocki's message of
"Wed, 9 Feb 2005 17:53:16 +0330")
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* Rafal Ramocki:
> I was writing a small script, but happened something wired.
This is not a bug, this is how floating point arithmetic works. In
binary floating point arithmetic, 0.01 has no exact representation
(like one third in decimal floating point). The errors pile up, and
after a few iterations of your loop, they become apparent.
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