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Re: Union test for endianess

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On 06/17/2011 10:53 PM, James Waldby wrote:
...
> On general purpose computers without special sensors, no portable 
> program can discover the relative spatial positions of electrons 
> that represent data bits, making physical order of bits irrelevant.

True.

> The logical succession order of bits in unsigned chars as revealed
> by C's <<, >> shift operators cannot differ from arithmetic order, 
> because C99 6.5.7 specifies <<, >> in terms of multiplication and
> division by powers of 2.  It appears that in the context of C99 C 
> there is only one possible bit succession order within unsigned bit 
> fields and unsigned chars, which is the 1, 2, 4... order referred to
> in footnote 40.

Not quite. C allows access to the object representation of an object as
an array of unsigned char. If I set an unsigned long object to store a
value of 1, It's a meaningful question to ask which bit of which byte is
set as a result. I believe that the standard's use of the term
"successive" should not be interpreted as mandating that it be the
lowest order bit of any of those bytes; it could be a bit that has a
value of 8 in the third byte, for instance.

I've heard of a platform where there was built-in support for floating
point math, but no hardware support for large integer types. A clumsy
work-around was created, that implemented a large integer type by using
floating point operations. For such an implementation, bits would almost
certainly not be found in any of the normally expected places in the
underlying array of unsigned char.
-- 
James Kuyper

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Union test for endianess Bhasker Penta <bskdsp@gmail.com> - 2011-06-16 20:16 -0700
  Re: Union test for endianess Ian Collins <ian-news@hotmail.com> - 2011-06-17 15:36 +1200
    Re: Union test for endianess Willem <willem@toad.stack.nl> - 2011-06-17 14:13 +0000
      Re: Union test for endianess Joe Wright <joewwright@comcast.net> - 2011-06-17 14:00 -0400
        Re: Union test for endianess Jorgen Grahn <grahn+nntp@snipabacken.se> - 2011-06-19 19:25 +0000
  Re: Union test for endianess China Blue Angels <chine.bleu@yahoo.com> - 2011-06-16 20:54 -0700
    Re: Union test for endianess Willem <willem@toad.stack.nl> - 2011-06-17 14:14 +0000
      Re: Union test for endianess James Kuyper <jameskuyper@verizon.net> - 2011-06-17 10:28 -0400
        Re: Union test for endianess Keith Thompson <kst-u@mib.org> - 2011-06-17 10:54 -0700
      Re: Union test for endianess Shao Miller <sha0.miller@gmail.com> - 2011-06-17 10:35 -0500
      Re: Union test for endianess "J. J. Farrell" <jjf@bcs.org.uk> - 2011-06-18 01:50 +0100
  Re: Union test for endianess China Blue Angels <chine.bleu@yahoo.com> - 2011-06-16 21:00 -0700
    Re: Union test for endianess Ben Bacarisse <ben.usenet@bsb.me.uk> - 2011-06-17 12:09 +0100
  Re: Union test for endianess Shao Miller <sha0.miller@gmail.com> - 2011-06-17 00:50 -0500
    Re: Union test for endianess Bhasker Penta <bskdsp@gmail.com> - 2011-06-16 23:17 -0700
      Re: Union test for endianess Shao Miller <sha0.miller@gmail.com> - 2011-06-17 03:01 -0500
        Re: Union test for endianess Shao Miller <sha0.miller@gmail.com> - 2011-06-17 13:33 -0500
          Re: Union test for endianess James Kuyper <jameskuyper@verizon.net> - 2011-06-18 09:18 -0400
          Re: Union test for endianess Shao Miller <sha0.miller@gmail.com> - 2011-06-19 17:22 -0500
          Re: Union test for endianess Tim Rentsch <txr@alumni.caltech.edu> - 2011-06-19 16:24 -0700
        Re: Union test for endianess Bhasker Penta <bskdsp@gmail.com> - 2011-06-18 01:08 -0700
        Re: Union test for endianess Tim Rentsch <txr@alumni.caltech.edu> - 2011-06-19 15:52 -0700
  Re: Union test for endianess James Kuyper <jameskuyper@verizon.net> - 2011-06-17 09:32 -0400
    Re: Union test for endianess James Kuyper <jameskuyper@verizon.net> - 2011-06-17 09:52 -0400
      Re: Union test for endianess Bhasker Penta <bskdsp@gmail.com> - 2011-06-17 07:13 -0700
        Re: Union test for endianess James Kuyper <jameskuyper@verizon.net> - 2011-06-17 10:31 -0400
    Re: Union test for endianess "christian.bau" <christian.bau@cbau.wanadoo.co.uk> - 2011-06-17 15:57 -0700
      Re: Union test for endianess Keith Thompson <kst-u@mib.org> - 2011-06-17 16:42 -0700
        Re: Union test for endianess James Waldby <not@valid.invalid> - 2011-06-18 02:53 +0000
          Re: Union test for endianess James Kuyper <jameskuyper@verizon.net> - 2011-06-17 23:59 -0400
            Re: Union test for endianess James Waldby <not@valid.invalid> - 2011-06-18 14:45 +0000
              Re: Union test for endianess James Kuyper <jameskuyper@verizon.net> - 2011-06-18 11:08 -0400
              Re: Union test for endianess cri@tiac.net (Richard Harter) - 2011-06-18 19:47 +0000
                Re: Union test for endianess James Waldby <not@valid.invalid> - 2011-06-18 23:15 +0000
                Re: Union test for endianess James Kuyper <jameskuyper@verizon.net> - 2011-06-18 22:42 -0400
              Re: Union test for endianess Jens <jens.gustedt@gmail.com> - 2011-06-19 07:41 -0700
              Re: Union test for endianess Roberto Waltman <usenet@rwaltman.com> - 2011-06-22 11:25 -0400
                Re: Union test for endianess James Kuyper <jameskuyper@verizon.net> - 2011-06-22 11:40 -0400
                Re: Union test for endianess James Waldby <not@valid.invalid> - 2011-06-22 21:42 +0000
      Re: Union test for endianess James Kuyper <jameskuyper@verizon.net> - 2011-06-17 21:18 -0400
  Re: Union test for endianess falk@rahul.net (Edward A. Falk) - 2011-06-17 20:50 +0000
  Re: Union test for endianess "Morris Keesan" <mkeesan@post.harvard.edu> - 2011-06-18 10:42 -0400
    Re: Union test for endianess Ben Bacarisse <ben.usenet@bsb.me.uk> - 2011-06-18 22:55 +0100
      Re: Union test for endianess "Morris Keesan" <mkeesan@post.harvard.edu> - 2011-06-19 21:14 -0400
  Re: Union test for endianess Jens <jens.gustedt@gmail.com> - 2011-06-19 07:46 -0700
    Re: Union test for endianess Tim Rentsch <txr@alumni.caltech.edu> - 2011-06-19 16:14 -0700
    Re: Union test for endianess Shao Miller <sha0.miller@gmail.com> - 2011-06-19 20:24 -0500
      Re: Union test for endianess Jens <jens.gustedt@gmail.com> - 2011-06-20 00:31 -0700
        Re: Union test for endianess Shao Miller <sha0.miller@gmail.com> - 2011-06-20 04:33 -0500
        Re: Union test for endianess Tim Rentsch <txr@alumni.caltech.edu> - 2011-06-20 12:22 -0700

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