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Re: Size of bool unspecified: why?

From "JBarleycorn" <jbnh2o@newsnet.org>
Newsgroups comp.lang.c++
Subject Re: Size of bool unspecified: why?
Date 2011-07-22 18:21 -0500
Organization A noiseless patient Spider
Message-ID <j0d0ld$45b$1@dont-email.me> (permalink)
References (2 earlier) <c8406a74-f3d9-4dd5-a3d7-3fb58c4d8ac0@l37g2000yqd.googlegroups.com> <j07eqo$qho$1@dont-email.me> <ca187bb0-9ac3-460c-b68c-b9167bc1edb4@g12g2000yqd.googlegroups.com> <j0ah1j$7fk$1@dont-email.me> <06bd239a-85d2-4b0c-bd8a-f435ef8cb3a6@ft10g2000vbb.googlegroups.com>

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"James Kanze" <james.kanze@gmail.com> wrote in message 
news:06bd239a-85d2-4b0c-bd8a-f435ef8cb3a6@ft10g2000vbb.googlegroups.com...
> On Jul 22, 1:42 am, "JBarleycorn" <jbn...@newsnet.org> wrote:

>> I have a feeling that "most" compilers by default expand all arguments
>> less than the "word" size to the "word" size.  Surely for simplicity 
>> of
>> implementation... stack offsets, etc.
>
> Most compilers do insert padding,

VC++ 2010 zero-extends unsigned ints of 8-bit before pushing them onto 
the stack as an arg. I just tested it because the documentation just says 
it "widens" and I had taken that, for some reason, to mean "by zero or 
sign extension" and wanted to know now if that was indeed the case, and 
it is so. Here's the doc: 
http://msdn.microsoft.com/en-us/library/984x0h58.aspx

> since not doing so will either
> slow the code down significantly (Intel) or cause the program to
> crash (most other processors) because of misaligned data.
> Inserting padding is not expanding an argument to word size;
> when a compiler inserts padding, the bytes in the padding have
> unspecified (and often random) values.  If I have something
> like:
>
>    void f( char ch );
>
>    char aChar;
>    f( aChar );
>
> I expect a compiler on an Intel to generate either:
>
>    push aChar
>
> (if `aChar` is correctly aligned), or
>
>    mov al, aChar
>    push eax
>
> to pass the argument.

No, it (VC++) does zero or sign extension before pushing the arg on the 
stack. Here is the relevant portion of the result of my test code:

; 26   :    pass8arg = Pass8(pass8arg);

 movzx ecx, BYTE PTR _pass8arg$[ebp]
 push ecx
 call ?Pass8@@YGEE@Z    ; Pass8
 mov BYTE PTR _pass8arg$[ebp], al

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Size of bool unspecified: why? "MikeP" <mp011011@some.org> - 2011-07-16 05:33 -0500
  Re: Size of bool unspecified: why? BGB <cr88192@hotmail.com> - 2011-07-16 10:02 -0700
    Re: Size of bool unspecified: why? James Kanze <james.kanze@gmail.com> - 2011-07-20 13:05 -0700
      Re: Size of bool unspecified: why? "JBarleycorn" <jbnh2o@newsnet.org> - 2011-07-20 15:46 -0500
        Re: Size of bool unspecified: why? Ian Collins <ian-news@hotmail.com> - 2011-07-21 09:01 +1200
          Re: Size of bool unspecified: why? "JBarleycorn" <jbnh2o@newsnet.org> - 2011-07-20 19:32 -0500
            Re: Size of bool unspecified: why? Ian Collins <ian-news@hotmail.com> - 2011-07-21 14:46 +1200
              Re: Size of bool unspecified: why? "JBarleycorn" <jbnh2o@newsnet.org> - 2011-07-20 23:28 -0500
                Re: Size of bool unspecified: why? Ian Collins <ian-news@hotmail.com> - 2011-07-21 16:43 +1200
                Re: Size of bool unspecified: why? "JBarleycorn" <jbnh2o@newsnet.org> - 2011-07-21 02:56 -0500
                Re: Size of bool unspecified: why? Ian Collins <ian-news@hotmail.com> - 2011-07-21 20:19 +1200
                Re: Size of bool unspecified: why? "JBarleycorn" <jbnh2o@newsnet.org> - 2011-07-21 18:29 -0500
                Re: Size of bool unspecified: why? Ian Collins <ian-news@hotmail.com> - 2011-07-22 11:40 +1200
                Re: Size of bool unspecified: why? "JBarleycorn" <jbnh2o@newsnet.org> - 2011-07-21 22:33 -0500
                Re: Size of bool unspecified: why? Ian Collins <ian-news@hotmail.com> - 2011-07-22 15:46 +1200
                Re: Size of bool unspecified: why? "JBarleycorn" <jbnh2o@newsnet.org> - 2011-07-21 23:07 -0500
                Re: Size of bool unspecified: why? Ian Collins <ian-news@hotmail.com> - 2011-07-22 16:12 +1200
                Re: Size of bool unspecified: why? Ian Collins <ian-news@hotmail.com> - 2011-07-31 18:45 +1200
                Re: Size of bool unspecified: why? Nick Keighley <nick_keighley_nospam@hotmail.com> - 2011-07-22 00:12 -0700
                Re: Size of bool unspecified: why? James Kanze <james.kanze@gmail.com> - 2011-07-22 11:10 -0700
                Re: Size of bool unspecified: why? "JBarleycorn" <jbnh2o@newsnet.org> - 2011-07-22 16:52 -0500
                Re: Size of bool unspecified: why? Ian Collins <ian-news@hotmail.com> - 2011-07-23 09:55 +1200
                Re: Size of bool unspecified: why? James Kanze <james.kanze@gmail.com> - 2011-07-22 11:01 -0700
                Re: Size of bool unspecified: why? "JBarleycorn" <jbnh2o@newsnet.org> - 2011-07-22 17:17 -0500
                Re: Size of bool unspecified: why? Ian Collins <ian-news@hotmail.com> - 2011-07-23 10:46 +1200
                Re: Size of bool unspecified: why? James Kanze <james.kanze@gmail.com> - 2011-07-24 03:48 -0700
                Re: Size of bool unspecified: why? Robert Wessel <robertwessel2@yahoo.com> - 2011-07-24 12:40 -0500
                Re: Size of bool unspecified: why? James Kanze <james.kanze@gmail.com> - 2011-07-30 11:22 -0700
                Re: Size of bool unspecified: why? "Alf P. Steinbach" <alf.p.steinbach:usenet@gmail.com> - 2011-07-31 02:33 +0200
                Re: Size of bool unspecified: why? James Kanze <james.kanze@gmail.com> - 2011-07-30 11:34 -0700
                Re: Size of bool unspecified: why? "Alf P. Steinbach" <alf.p.steinbach:usenet@gmail.com> - 2011-07-25 04:46 +0200
                Re: Size of bool unspecified: why? James Kanze <james.kanze@gmail.com> - 2011-07-21 07:23 -0700
                Re: Size of bool unspecified: why? "JBarleycorn" <jbnh2o@newsnet.org> - 2011-07-21 18:52 -0500
                Re: Size of bool unspecified: why? James Kanze <james.kanze@gmail.com> - 2011-07-22 11:24 -0700
                Re: Size of bool unspecified: why? "JBarleycorn" <jbnh2o@newsnet.org> - 2011-07-22 17:22 -0500
                Re: Size of bool unspecified: why? Ian Collins <ian-news@hotmail.com> - 2011-07-23 10:51 +1200
                Re: Size of bool unspecified: why? Nick Keighley <nick_keighley_nospam@hotmail.com> - 2011-07-22 00:17 -0700
                Re: Size of bool unspecified: why? Robert Wessel <robertwessel2@yahoo.com> - 2011-07-22 04:26 -0500
            Re: Size of bool unspecified: why? James Kanze <james.kanze@gmail.com> - 2011-07-21 02:09 -0700
              Re: Size of bool unspecified: why? "JBarleycorn" <jbnh2o@newsnet.org> - 2011-07-21 19:11 -0500
                Re: Size of bool unspecified: why? James Kanze <james.kanze@gmail.com> - 2011-07-22 11:58 -0700
                Re: Size of bool unspecified: why? "JBarleycorn" <jbnh2o@newsnet.org> - 2011-07-22 17:48 -0500
            Re: Size of bool unspecified: why? Nick Keighley <nick_keighley_nospam@hotmail.com> - 2011-07-21 08:41 -0700
              Re: Size of bool unspecified: why? "JBarleycorn" <jbnh2o@newsnet.org> - 2011-07-21 19:14 -0500
                Re: Size of bool unspecified: why? James Kanze <james.kanze@gmail.com> - 2011-07-22 12:01 -0700
                Re: Size of bool unspecified: why? "JBarleycorn" <jbnh2o@newsnet.org> - 2011-07-22 17:51 -0500
        Re: Size of bool unspecified: why? Noah Roberts <dont@email.me> - 2011-07-20 16:57 -0700
          Re: Size of bool unspecified: why? James Kanze <james.kanze@gmail.com> - 2011-07-21 07:29 -0700
            Re: Size of bool unspecified: why? "JBarleycorn" <jbnh2o@newsnet.org> - 2011-07-21 19:24 -0500
              Re: Size of bool unspecified: why? Ian Collins <ian-news@hotmail.com> - 2011-07-22 12:33 +1200
                Re: Size of bool unspecified: why? "JBarleycorn" <jbnh2o@newsnet.org> - 2011-07-21 22:42 -0500
        Re: Size of bool unspecified: why? James Kanze <james.kanze@gmail.com> - 2011-07-21 01:59 -0700
          Re: Size of bool unspecified: why? "JBarleycorn" <jbnh2o@newsnet.org> - 2011-07-21 19:42 -0500
            Re: Size of bool unspecified: why? James Kanze <james.kanze@gmail.com> - 2011-07-22 12:20 -0700
              Re: Size of bool unspecified: why? "JBarleycorn" <jbnh2o@newsnet.org> - 2011-07-22 18:21 -0500
  Re: Size of bool unspecified: why? Robert Wessel <robertwessel2@yahoo.com> - 2011-07-16 22:23 -0500
    Re: Size of bool unspecified: why? "MikeP" <mp011011@some.org> - 2011-07-17 00:07 -0500
      Re: Size of bool unspecified: why? Ian Collins <ian-news@hotmail.com> - 2011-07-17 17:15 +1200
        Re: Size of bool unspecified: why? "MikeP" <mp011011@some.org> - 2011-07-17 00:24 -0500
      Re: Size of bool unspecified: why? Robert Wessel <robertwessel2@yahoo.com> - 2011-07-17 02:02 -0500
        Re: Size of bool unspecified: why? "MikeP" <mp011011@some.org> - 2011-07-17 03:02 -0500
          Re: Size of bool unspecified: why? Robert Wessel <robertwessel2@yahoo.com> - 2011-07-17 03:23 -0500
            Re: Size of bool unspecified: why? "MikeP" <mp011011@some.org> - 2011-07-17 05:36 -0500
              Re: Size of bool unspecified: why? "James" <no@spam.invalid> - 2011-07-17 16:24 -0700
                Re: Size of bool unspecified: why? "MikeP" <mp011011@some.org> - 2011-07-18 06:49 -0500
                Re: Size of bool unspecified: why? "James" <no@spam.invalid> - 2011-07-18 16:46 -0700
                Re: Size of bool unspecified: why? Ian Collins <ian-news@hotmail.com> - 2011-07-19 11:59 +1200
                Re: Size of bool unspecified: why? "MikeP" <mp011011@some.org> - 2011-07-19 22:18 -0500
        Re: Size of bool unspecified: why? "MikeP" <mp011011@some.org> - 2011-07-17 03:04 -0500
      Re: Size of bool unspecified: why? Nick Keighley <nick_keighley_nospam@hotmail.com> - 2011-07-22 00:32 -0700
      Re: Size of bool unspecified: why? Nick Keighley <nick_keighley_nospam@hotmail.com> - 2011-07-22 00:41 -0700
  Re: Size of bool unspecified: why? Juha Nieminen <nospam@thanks.invalid> - 2011-07-17 13:50 +0000
    Re: Size of bool unspecified: why? "MikeP" <mp011011@some.org> - 2011-07-18 06:50 -0500
      Re: Size of bool unspecified: why? James Kanze <james.kanze@gmail.com> - 2011-07-20 13:06 -0700
    Re: Size of bool unspecified: why? Pawel Dziepak <pdziepak@quarnos.org> - 2011-07-21 12:59 +0000
      Re: Size of bool unspecified: why? James Kanze <james.kanze@gmail.com> - 2011-07-21 07:11 -0700
        Re: Size of bool unspecified: why? "JBarleycorn" <jbnh2o@newsnet.org> - 2011-07-21 19:21 -0500
          Re: Size of bool unspecified: why? James Kanze <james.kanze@gmail.com> - 2011-07-22 12:28 -0700

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