From: Christian Luginbuehl <dinkel@...>
Date: 2007-08-20T02:49:28+09:00
Subject: Float addition problem / Processor bug?

Hi,

Check out this weird IRB output:

=== START ===
irb(main):001:0> a = 2.95 + 2.95 + 2.95
=> 8.85
irb(main):002:0> puts 8.85 - a
-1.77635683940025e-15
=> nil
=== END ===

I'm running "ruby 1.8.6 (2007-06-07 patchlevel 36) [i486-linux]" on 
Xubuntu beta with this processor:

=== START cat /proc/cpuinfo ===
processor       : 0
vendor_id       : GenuineIntel
cpu family      : 15
model           : 2
model name      : Intel(R) Pentium(R) 4 CPU 2.26GHz
stepping        : 4
cpu MHz         : 2271.951
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 clflush dts acpi mmx fxsr sse sse2 ss ht tm up
bogomips        : 4547.85
clflush size    : 64
=== END cat /proc/cpuinfo ===

Is it a processor bug, a simple rounding problem or a ruby error?

How do I proceed?

Thanks,

Dinkel