From: Colin Bartlett <colinb2r@...>
Date: 2009-09-16T03:07:29+09:00
Subject: Re: Overflow behavior

--001485f6c5c68051260473a1a787
Content-Type: text/plain; charset=ISO-8859-1

On Tue, Sep 15, 2009 at 2:08 AM, David Masover <ninja@slaphack.com> wrote:
> irb(main):009:0> (2**62-1).class    => Fixnum
> irb(main):010:0> (2**62).class      => Bignum
> irb(main):012:0> ((-2)**62-1).class => Fixnum
> irb(main):013:0> ((-2)**62).class   => Bignum
> Fixnum seems to be a signed 63-bit integer (62 bits plus the sign bit) on
my 64-bit system.
> I'm guessing that it's actually a 31-bit signed integer on a 32-bit
system.
*
Fixnum/Bignum is implementation dependent?
On a Win32 Vista PC (with IRB/JIRB output cleaned up & aligned by hand):
*
Ruby 1.8.6 IRB:
n = if RUBY_PLATFORM.downcase == "java" then 63 else 30 end  #=> 30
nn = 2 ** n - 1 ; "#{nn.class}  #{nn}"  #=> Fixnum   1073741823
nn = -nn        ; "#{nn.class}  #{nn}"  #=> Fixnum  -1073741823
nn = 2 ** n     ; "#{nn.class}  #{nn}"  #=> Bignum   1073741824
nn = -nn        ; "#{nn.class}  #{nn}"  #=> Fixnum  -1073741824
nn = 2 ** n + 1 ; "#{nn.class}  #{nn}"  #=> Bignum   1073741825
nn = -nn        ; "#{nn.class}  #{nn}"  #=> Bignum  -1073741825
*
JRuby 1.3.1 JIRB:
n = if RUBY_PLATFORM.downcase == "java" then 63 else 30 end  #=> 63
nn = 2 ** n - 1 ; "#{nn.class}  #{nn}"  #=> Fixnum   9223372036854775807
nn = -nn        ; "#{nn.class}  #{nn}"  #=> Fixnum  -9223372036854775807
nn = 2 ** n     ; "#{nn.class}  #{nn}"  #=> Bignum   9223372036854775808
nn = -nn        ; "#{nn.class}  #{nn}"  #=> Fixnum  -9223372036854775808
nn = 2 ** n + 1 ; "#{nn.class}  #{nn}"  #=> Bignum   9223372036854775809
nn = -nn        ; "#{nn.class}  #{nn}"  #=> Bignum  -9223372036854775809

--001485f6c5c68051260473a1a787--