From: "Ara.T.Howard" <ahoward@...>
Date: 2004-02-19T01:54:54+09:00
Subject: Re: Ruby 1.8.1: Unexpected "pack" result

On Thu, 19 Feb 2004, Dale Martenson wrote:

> Date: Thu, 19 Feb 2004 00:05:53 +0900
> From: Dale Martenson <dmartenson@multitech.com>
> Newsgroups: comp.lang.ruby
> Subject: Ruby 1.8.1: Unexpected "pack" result
> 
> I noticed something that does seem correct. In an application I have been
> shipping, I pack value in order to perform IOCTL calls against a device. I
> hit a problem when using Ruby 1.8.1. The following worked in 1.6.7 and
> 1.8.0:
> 
>           [ 0xFFFFFFFF ].pack("i")
> 
> In 1.8.1, this raises a "Range Error: bignum to big to convert into 'int'".
> 
> I understood that an "i" designator meant a signed native integer (32-bits).
> I don't see why this should fail. 
> 
> Also, if I use the "l" designator to indicate a signed long integer (again
> 32-bits). Everything works.
> 
>           [ 0xFFFFFFFF ].pack("l")
> 
> Shouldn't "i" and "l" act the same if the native size of an integer is
> 32-bits?

well, it looks like the orginal code was the problem:


  ~ > cat int_max.rb 

    require 'tmpdir'
    require 'ftools'

    c_prog = <<-code
      #include <limits.h>
      main(){int i = INT_MAX; write(1,&i,sizeof(int));}
    code

    tmp = Dir::tmpdir

    a_c = File.join tmp, 'a.c' 
    a_out = File.join tmp, 'a.out' 
    out = File.join tmp, 'out' 

    open(a_c, 'w'){|f| f.write c_prog}
    system "cc #{ a_c } -o #{ a_out }"
    system "#{ a_out } > #{ out }"

    int_max = IO.read(out).unpack('i').first

    p(int_max)
    p((2 ** 31) - 1)
    p(0xFFFFFFFF)
    p((2 ** 32) - 1)


    File.rm_f a_c
    File.rm_f a_out
    File.rm_f out

  ~ > ruby int_max.rb 

    2147483647
    2147483647
    4294967295
    4294967295



you only get 31 bits for signed ints.

-a
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