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Re: C/C++ pitfalls related to 64-bits (unsigned long & double)

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On 02/14/2012 12:53 PM, Lowell Gilbert wrote:
> Keith Thompson <kst-u@mib.org> writes:
> 
>> Ben Bacarisse <ben.usenet@bsb.me.uk> writes:
>>> BGB <cr88192@hotmail.com> writes:
>> [...]
>>>> as I understand it, the entire range of 32 bit integers can be exactly
>>>> represented by a double.
>>>
>>> In the architecture in question, yes.
>> [...]
>>
>> In any conforming C implementation; the requirements on double are such
>> that it can represent any 32-bit integer value exactly.
> 
> Because of the Usual Arithmetic Conversions, 
> or is there some other reason?

Those rules tell you what conversions must occur; they don't tell you
what the results must be, and in particular they don't tell you anything
about which values can be represented exactly.

Section 5.2.4.2.2, "Characteristics of floating types" describes a model
for a floating point representation. An implementation is not required
to use precisely that representation, but it must use one that's
sufficiently similar that it's characteristics can be described in terms
of that model.  In that model, the smallest integer that cannot be
represented exactly is pow(b,p+1)+1. Paragraph 11 requires that
FLT_RADIX, (corresponding to 'b' in the model) must be an integer with a
value of at least 2. Paragraph 13 requires that DBL_EPSILON
(corresponding to pow(b,1-p) in the model) must be 1e-9 or smaller,
which imposes a minimum value of p for any given b.

The description of 'p' implies, but does not explicitly require, that it
is an integer. I can't figure out how a non-integral value for 'p' could
be implemented. With integer values for both b  and p, the smallest
value you can get for an unrepresentable integer occurs for b==2 and
p==31, for which DBL_EPSILON is 2^-30; the corresponding smallest
unrepresentable integer is 2^32+1.

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C/C++ pitfalls related to 64-bits (unsigned long & double) Alex Vinokur <alex.vinokur@gmail.com> - 2012-02-13 04:41 -0800
  Re: C/C++ pitfalls related to 64-bits (unsigned long & double) Leigh Johnston <leigh@i42.co.uk> - 2012-02-13 12:49 +0000
    Re: C/C++ pitfalls related to 64-bits (unsigned long & double) Alex Vinokur <alex.vinokur@gmail.com> - 2012-02-13 04:59 -0800
      Re: C/C++ pitfalls related to 64-bits (unsigned long & double) Leigh Johnston <leigh@i42.co.uk> - 2012-02-13 13:07 +0000
  Re: C/C++ pitfalls related to 64-bits (unsigned long & double) Goran <goran.pusic@gmail.com> - 2012-02-13 04:54 -0800
    Re: C/C++ pitfalls related to 64-bits (unsigned long & double) Alex Vinokur <alex.vinokur@gmail.com> - 2012-02-13 05:00 -0800
    Re: C/C++ pitfalls related to 64-bits (unsigned long & double) Ben Bacarisse <ben.usenet@bsb.me.uk> - 2012-02-13 13:27 +0000
    Re: C/C++ pitfalls related to 64-bits (unsigned long & double) Goran <goran.pusic@gmail.com> - 2012-02-13 07:14 -0800
  Re: C/C++ pitfalls related to 64-bits (unsigned long & double) Eric Sosman <esosman@ieee-dot-org.invalid> - 2012-02-13 08:14 -0500
    Re: C/C++ pitfalls related to 64-bits (unsigned long & double) Eric Sosman <esosman@ieee-dot-org.invalid> - 2012-02-13 08:17 -0500
      Re: C/C++ pitfalls related to 64-bits (unsigned long & double) glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2012-02-13 21:52 +0000
        Re: C/C++ pitfalls related to 64-bits (unsigned long & double) James Kuyper <jameskuyper@verizon.net> - 2012-02-13 17:08 -0500
        Re: C/C++ pitfalls related to 64-bits (unsigned long & double) Eric Sosman <esosman@ieee-dot-org.invalid> - 2012-02-13 20:44 -0500
  Re: C/C++ pitfalls related to 64-bits (unsigned long & double) Ben Bacarisse <ben.usenet@bsb.me.uk> - 2012-02-13 13:16 +0000
    Re: C/C++ pitfalls related to 64-bits (unsigned long & double) BGB <cr88192@hotmail.com> - 2012-02-13 11:18 -0700
      Re: C/C++ pitfalls related to 64-bits (unsigned long & double) "MikeWhy" <boat042-nospam@yahoo.com> - 2012-02-13 15:18 -0600
        Re: C/C++ pitfalls related to 64-bits (unsigned long & double) James Kuyper <jameskuyper@verizon.net> - 2012-02-13 16:26 -0500
          Re: C/C++ pitfalls related to 64-bits (unsigned long & double) "MikeWhy" <boat042-nospam@yahoo.com> - 2012-02-13 16:05 -0600
            Re: C/C++ pitfalls related to 64-bits (unsigned long & double) James Kuyper <jameskuyper@verizon.net> - 2012-02-13 17:13 -0500
              Re: C/C++ pitfalls related to 64-bits (unsigned long & double) Ben Bacarisse <ben.usenet@bsb.me.uk> - 2012-02-13 23:35 +0000
                Re: C/C++ pitfalls related to 64-bits (unsigned long & double) BGB <cr88192@hotmail.com> - 2012-02-13 17:25 -0700
                Re: C/C++ pitfalls related to 64-bits (unsigned long & double) Ben Bacarisse <ben.usenet@bsb.me.uk> - 2012-02-14 01:45 +0000
                Re: C/C++ pitfalls related to 64-bits (unsigned long & double) BGB <cr88192@hotmail.com> - 2012-02-13 18:55 -0700
                Re: C/C++ pitfalls related to 64-bits (unsigned long & double) Miles Bader <miles@gnu.org> - 2012-02-14 11:51 +0900
                Re: C/C++ pitfalls related to 64-bits (unsigned long & double) Ben Bacarisse <ben.usenet@bsb.me.uk> - 2012-02-14 03:13 +0000
                Re: C/C++ pitfalls related to 64-bits (unsigned long & double) BGB <cr88192@hotmail.com> - 2012-02-13 20:39 -0700
                Re: C/C++ pitfalls related to 64-bits (unsigned long & double) Miles Bader <miles@gnu.org> - 2012-02-14 13:25 +0900
                Re: C/C++ pitfalls related to 64-bits (unsigned long & double) BGB <cr88192@hotmail.com> - 2012-02-13 23:22 -0700
                Re: C/C++ pitfalls related to 64-bits (unsigned long & double) "MikeWhy" <boat042-nospam@yahoo.com> - 2012-02-14 02:56 -0600
                Re: C/C++ pitfalls related to 64-bits (unsigned long & double) BGB <cr88192@hotmail.com> - 2012-02-14 09:13 -0700
                Re: C/C++ pitfalls related to 64-bits (unsigned long & double) "MikeWhy" <boat042-nospam@yahoo.com> - 2012-02-14 11:16 -0600
                Re: C/C++ pitfalls related to 64-bits (unsigned long & double) BGB <cr88192@hotmail.com> - 2012-02-14 12:27 -0700
                Re: C/C++ pitfalls related to 64-bits (unsigned long & double) Eric Sosman <esosman@ieee-dot-org.invalid> - 2012-02-13 23:04 -0500
                Re: C/C++ pitfalls related to 64-bits (unsigned long & double) Miles Bader <miles@gnu.org> - 2012-02-14 14:00 +0900
                Re: C/C++ pitfalls related to 64-bits (unsigned long & double) Robert Wessel <robertwessel2@yahoo.com> - 2012-02-14 00:45 -0600
                Re: C/C++ pitfalls related to 64-bits (unsigned long & double) glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2012-02-14 14:22 +0000
                Re: C/C++ pitfalls related to 64-bits (unsigned long & double) Robert Wessel <robertwessel2@yahoo.com> - 2012-02-14 13:06 -0600
                Re: C/C++ pitfalls related to 64-bits (unsigned long & double) BGB <cr88192@hotmail.com> - 2012-02-14 12:40 -0700
                Re: C/C++ pitfalls related to 64-bits (unsigned long & double) James Kuyper <jameskuyper@verizon.net> - 2012-02-13 23:05 -0500
                Re: C/C++ pitfalls related to 64-bits (unsigned long & double) Miles Bader <miles@gnu.org> - 2012-02-14 14:01 +0900
                Re: C/C++ pitfalls related to 64-bits (unsigned long & double) Keith Thompson <kst-u@mib.org> - 2012-02-14 03:01 -0800
                Re: C/C++ pitfalls related to 64-bits (unsigned long & double) Lowell Gilbert <lgusenet@be-well.ilk.org> - 2012-02-14 12:53 -0500
                Re: C/C++ pitfalls related to 64-bits (unsigned long & double) James Kuyper <jameskuyper@verizon.net> - 2012-02-14 14:39 -0500
            Re: C/C++ pitfalls related to 64-bits (unsigned long & double) jgk@panix.com (Joe keane) - 2012-02-14 20:45 +0000
              Re: C/C++ pitfalls related to 64-bits (unsigned long & double) glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2012-02-14 22:57 +0000
              Re: C/C++ pitfalls related to 64-bits (unsigned long & double) Keith Thompson <kst-u@mib.org> - 2012-02-14 15:38 -0800
                Re: C/C++ pitfalls related to 64-bits (unsigned long & double) glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2012-02-15 00:22 +0000
                Re: C/C++ pitfalls related to 64-bits (unsigned long & double) Robert Wessel <robertwessel2@yahoo.com> - 2012-02-15 00:39 -0600
                Re: C/C++ pitfalls related to 64-bits (unsigned long & double) glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2012-02-15 08:00 +0000
      Re: C/C++ pitfalls related to 64-bits (unsigned long & double) Ben Bacarisse <ben.usenet@bsb.me.uk> - 2012-02-13 22:00 +0000
        Re: C/C++ pitfalls related to 64-bits (unsigned long & double) BGB <cr88192@hotmail.com> - 2012-02-13 17:04 -0700
          Re: C/C++ pitfalls related to 64-bits (unsigned long & double) Malcolm McLean <malcolm.mclean5@btinternet.com> - 2012-02-13 16:15 -0800
          Re: C/C++ pitfalls related to 64-bits (unsigned long & double) Ben Bacarisse <ben.usenet@bsb.me.uk> - 2012-02-14 00:46 +0000
            Re: C/C++ pitfalls related to 64-bits (unsigned long & double) BGB <cr88192@hotmail.com> - 2012-02-13 18:31 -0700
              Re: C/C++ pitfalls related to 64-bits (unsigned long & double) BGB <cr88192@hotmail.com> - 2012-02-13 18:41 -0700
                Re: C/C++ pitfalls related to 64-bits (unsigned long & double) Ben Bacarisse <ben.usenet@bsb.me.uk> - 2012-02-14 02:33 +0000
                Re: C/C++ pitfalls related to 64-bits (unsigned long & double) BGB <cr88192@hotmail.com> - 2012-02-13 20:20 -0700
                Re: C/C++ pitfalls related to 64-bits (unsigned long & double) Ben Bacarisse <ben.usenet@bsb.me.uk> - 2012-02-14 03:26 +0000
                Re: C/C++ pitfalls related to 64-bits (unsigned long & double) BGB <cr88192@hotmail.com> - 2012-02-13 20:49 -0700
              Re: C/C++ pitfalls related to 64-bits (unsigned long & double) Robert Wessel <robertwessel2@yahoo.com> - 2012-02-14 00:24 -0600
                Re: C/C++ pitfalls related to 64-bits (unsigned long & double) BGB <cr88192@hotmail.com> - 2012-02-13 23:42 -0700
                Re: C/C++ pitfalls related to 64-bits (unsigned long & double) James Kuyper <jameskuyper@verizon.net> - 2012-02-14 06:48 -0500
                Re: C/C++ pitfalls related to 64-bits (unsigned long & double) Ben Bacarisse <ben.usenet@bsb.me.uk> - 2012-02-14 13:51 +0000
                Re: C/C++ pitfalls related to 64-bits (unsigned long & double) BGB <cr88192@hotmail.com> - 2012-02-14 08:42 -0700
                Re: C/C++ pitfalls related to 64-bits (unsigned long & double) glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2012-02-14 19:58 +0000
                Re: C/C++ pitfalls related to 64-bits (unsigned long & double) glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2012-02-14 14:27 +0000
                Re: C/C++ pitfalls related to 64-bits (unsigned long & double) BGB <cr88192@hotmail.com> - 2012-02-14 09:10 -0700
                Re: C/C++ pitfalls related to 64-bits (unsigned long & double) glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2012-02-14 20:02 +0000
  Re: C/C++ pitfalls related to 64-bits (unsigned long & double) Noob <root@127.0.0.1> - 2012-02-13 15:22 +0100
  Re: C/C++ pitfalls related to 64-bits (unsigned long & double) legalize+jeeves@mail.xmission.com (Richard) - 2012-02-13 18:49 +0000
    Re: C/C++ pitfalls related to 64-bits (unsigned long & double) James Kuyper <jameskuyper@verizon.net> - 2012-02-13 13:55 -0500
      Re: C/C++ pitfalls related to 64-bits (unsigned long & double) Juha Nieminen <nospam@thanks.invalid> - 2012-02-13 19:14 +0000
  Re: C/C++ pitfalls related to 64-bits (unsigned long & double) Barry Schwarz <schwarzb@dqel.com> - 2012-02-13 12:14 -0800

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