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Re: return -1 using size_t???

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Ben Bacarisse <ben.usenet@bsb.me.uk> writes:

> Ike Naar <ike@sverige.freeshell.org> writes:
>
>> On 2012-02-12, Ben Bacarisse <ben.usenet@bsb.me.uk> wrote:
>>> Keith Thompson <kst-u@mib.org> writes:
>>> There is one that does both (selectable as an option).  I just happened
>>> to be reading a Unisys C manual[1] recently.  It's part of MCP: Unisys's
>>> OS that runs on big machines derived from a Burroughs architecture.  It
>>> has 48-bit words and 8-bit bytes.
>>>
>>>  sizeof char/unsigned char/signed char is 1
>>>  sizeof long double is 12
>>>  sizeof everything else is 6
>>>
>>> Despite having 48 bits, all integer types have 39 value bits.  Signed
>>> types have, in addition, a sign bit (presumably the 40th).  The
>>> remaining bits are presumably related to the tagged architecture that
>>> Burroughs machines have always had and, as far as C goes, will be
>>> padding bits.  These machine will definitely have trap-representations,
>>> since some sets of these tag bits are designed to cause traps in certain
>>> situations.
>>
>> Having worked with these systems in the early 1980's, I remember
>> that integers are just floating point numbers where the 8-bit exponent
>> contains all zeroes, and the (1+39)-bit mantissa holds the value.
>
> Ah, that makes sense.  There were, I think, CDC machines that did that
> too.  Do you know what happened when exponent bits got set (and indeed
> if they could get set) by operations like ~?

Well, sort-of.  They did use a representation in which having the sign
and exponent bits all 0 or all 1 would give the same result as an
integer, but they had separate integer and floating point instructions
so an integer add (for instance) could use all 60 bits for value.

The one exception to that rule was multiplication:  there were only
floating point multiplication instructions, but the "double precision"
multiply would correctly multiply two integers, provided the result fit
in 48 (iirc) bits.

I've come across the claim many times that this was in fact an accident
that wasn't noticed until the machine was in production, but haven't
come across any substantiation of it.  I don't think Thornton's book
mentions that you can do this (but could easily be mis-remembering).

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return -1 using size_t??? Robert Hayes <rhyes80@gmail.com> - 2012-02-11 11:21 -0800
  Re: return -1 using size_t??? Shao Miller <sha0.miller@gmail.com> - 2012-02-11 15:00 -0500
    Re: return -1 using size_t??? Ben Bacarisse <ben.usenet@bsb.me.uk> - 2012-02-11 23:24 +0000
  Re: return -1 using size_t??? Jeffrey R <joeff@nospam.com> - 2012-02-11 19:58 +0000
    Re: return -1 using size_t??? Eric Sosman <esosman@ieee-dot-org.invalid> - 2012-02-11 15:11 -0500
  Re: return -1 using size_t??? Eric Sosman <esosman@ieee-dot-org.invalid> - 2012-02-11 15:07 -0500
    Re: return -1 using size_t??? Robert Hayes <rhyes80@gmail.com> - 2012-02-11 12:42 -0800
      Re: return -1 using size_t??? Malcolm McLean <malcolm.mclean5@btinternet.com> - 2012-02-11 13:19 -0800
        Re: return -1 using size_t??? Keith Thompson <kst-u@mib.org> - 2012-02-11 17:10 -0800
          Re: return -1 using size_t??? Malcolm McLean <malcolm.mclean5@btinternet.com> - 2012-02-12 03:48 -0800
            Re: return -1 using size_t??? Keith Thompson <kst-u@mib.org> - 2012-02-12 04:04 -0800
      Re: return -1 using size_t??? Jeffrey R <joeff@nospam.com> - 2012-02-11 22:25 +0000
        Re: return -1 using size_t??? Devil with the China Blue Dress <chine.bleu@yahoo.com> - 2012-02-11 14:36 -0800
          Re: return -1 using size_t??? Ben Bacarisse <ben.usenet@bsb.me.uk> - 2012-02-11 23:17 +0000
        Re: return -1 using size_t??? Jeroen Mostert <jmostert@xs4all.nl> - 2012-02-11 23:46 +0100
          Re: return -1 using size_t??? pete <pfiland@mindspring.com> - 2012-02-11 19:18 -0500
        Re: return -1 using size_t??? Eric Sosman <esosman@ieee-dot-org.invalid> - 2012-02-12 08:38 -0500
      Re: return -1 using size_t??? Ben Bacarisse <ben.usenet@bsb.me.uk> - 2012-02-11 23:32 +0000
      Re: return -1 using size_t??? pete <pfiland@mindspring.com> - 2012-02-11 19:15 -0500
    Re: return -1 using size_t??? Ralph Spitzner <rasp@spitzner.org> - 2012-02-13 13:51 +0100
  Re: return -1 using size_t??? Devil with the China Blue Dress <chine.bleu@yahoo.com> - 2012-02-11 12:40 -0800
    Re: return -1 using size_t??? Eric Sosman <esosman@ieee-dot-org.invalid> - 2012-02-11 17:02 -0500
      Re: return -1 using size_t??? Devil with the China Blue Dress <chine.bleu@yahoo.com> - 2012-02-11 14:11 -0800
        Re: return -1 using size_t??? Eric Sosman <esosman@ieee-dot-org.invalid> - 2012-02-11 17:21 -0500
          Re: return -1 using size_t??? Devil with the China Blue Dress <chine.bleu@yahoo.com> - 2012-02-11 14:31 -0800
            Re: return -1 using size_t??? Willem <willem@toad.stack.nl> - 2012-02-11 22:52 +0000
            Re: return -1 using size_t??? Jens Gustedt <jens.gustedt@loria.fr> - 2012-02-12 00:20 +0100
              Re: return -1 using size_t??? Devil with the China Blue Dress <chine.bleu@yahoo.com> - 2012-02-12 09:21 -0800
                Re: return -1 using size_t??? Keith Thompson <kst-u@mib.org> - 2012-02-12 12:27 -0800
                Re: return -1 using size_t??? Jeroen Mostert <jmostert@xs4all.nl> - 2012-02-12 22:17 +0100
                Re: return -1 using size_t??? Devil with the China Blue Dress <chine.bleu@yahoo.com> - 2012-02-12 15:10 -0800
                Re: return -1 using size_t??? Nick Keighley <nick_keighley_nospam@hotmail.com> - 2012-02-13 03:11 -0800
                Re: return -1 using size_t??? Ben Bacarisse <ben.usenet@bsb.me.uk> - 2012-02-12 23:25 +0000
                Re: return -1 using size_t??? Jeroen Mostert <jmostert@xs4all.nl> - 2012-02-13 07:46 +0100
                Re: return -1 using size_t??? Ike Naar <ike@sverige.freeshell.org> - 2012-02-13 10:27 +0000
                Re: return -1 using size_t??? Ben Bacarisse <ben.usenet@bsb.me.uk> - 2012-02-13 12:36 +0000
                Re: return -1 using size_t??? Joe Pfeiffer <pfeiffer@cs.nmsu.edu> - 2012-02-13 10:26 -0700
                Re: return -1 using size_t??? Ike Naar <ike@iceland.freeshell.org> - 2012-02-14 00:18 +0000
                Re: return -1 using size_t??? Ben Bacarisse <ben.usenet@bsb.me.uk> - 2012-02-14 00:29 +0000
                Re: return -1 using size_t??? Devil with the China Blue Dress <chine.bleu@yahoo.com> - 2012-02-13 16:37 -0800
                Re: return -1 using size_t??? Angel <angel+news@spamcop.net> - 2012-02-13 11:47 +0000
                Re: return -1 using size_t??? Ben Bacarisse <ben.usenet@bsb.me.uk> - 2012-02-13 12:54 +0000
                Re: return -1 using size_t??? Angel <angel+news@spamcop.net> - 2012-02-13 14:30 +0000
                Re: return -1 using size_t??? Phil Carmody <thefatphil_demunged@yahoo.co.uk> - 2012-02-22 01:53 +0200
                Re: return -1 using size_t??? James Kuyper <jameskuyper@verizon.net> - 2012-02-13 12:11 -0500
                Re: return -1 using size_t??? Ben Bacarisse <ben.usenet@bsb.me.uk> - 2012-02-13 17:28 +0000
                Re: return -1 using size_t??? James Kuyper <jameskuyper@verizon.net> - 2012-02-13 13:08 -0500
                Re: return -1 using size_t??? Ben Bacarisse <ben.usenet@bsb.me.uk> - 2012-02-13 23:06 +0000
                Re: return -1 using size_t??? William Ahern <william@wilbur.25thandClement.com> - 2012-02-13 14:39 -0800
                Re: return -1 using size_t??? Keith Thompson <kst-u@mib.org> - 2012-02-13 14:59 -0800
                Re: return -1 using size_t??? Jens Gustedt <jens.gustedt@loria.fr> - 2012-02-12 22:17 +0100
                Re: return -1 using size_t??? Devil with the China Blue Dress <chine.bleu@yahoo.com> - 2012-02-12 15:06 -0800
                Re: return -1 using size_t??? Eric Sosman <esosman@ieee-dot-org.invalid> - 2012-02-12 18:12 -0500
                Re: return -1 using size_t??? Phil Carmody <thefatphil_demunged@yahoo.co.uk> - 2012-02-22 02:15 +0200
  Re: return -1 using size_t??? Barry Schwarz <schwarzb@dqel.com> - 2012-02-11 14:27 -0800
    Re: return -1 using size_t??? Keith Thompson <kst-u@mib.org> - 2012-02-11 17:34 -0800

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