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Re: [OT] Re: Why would one use += 1 at the place of ++?

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On 5/19/2011 5:58 PM, David Lamb wrote:
> On 19/05/2011 8:03 AM, Eric Sosman wrote:
>> On 5/19/2011 6:40 AM, David Lamb wrote:
>>> [...]
>>> I think ++ exists only because the hardware on which C was developed had
>>> an addressing mode that did it atomically in the very special case of
>>> referring to
>>> something = array[index++];
>>
>> FWIW, some guy named Dennis Ritchie says this is not true.
>
> He ought to know.
>
>> "People often guess that [++ and --]were created to use the
>> auto-increment and auto-decrement address modes provided
>> by the DEC PDP-11 on which C and Unix first became popular.
>> This is historically impossible, since there was no PDP-11
>> when B was developed."
>
> I had the idea that this arose from some machine where lowest small
> number of locations in memory had some form of autoincrementing when you
> used them as array indices, but that sounds so weird I may be
> hallucinating.

     Ritchie mentions such a machine (the PDP-7), but also says the
special hardware was not actually used in the implementations of ++
and -- (either prefix or postfix).  He speculates that they might have
put the idea into Thompson's head, though.  The full paper is at

	http://cm.bell-labs.com/cm/cs/who/dmr/chist.html

for folks of an archaeological bent.

-- 
Eric Sosman
esosman@ieee-dot-org.invalid

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Why would one use += 1 at the place of ++? Merciadri Luca <Luca.Merciadri@student.ulg.ac.be> - 2011-05-19 09:19 +0200
  Re: Why would one use += 1 at the place of ++? Bent C Dalager <bcd@pvv.ntnu.no> - 2011-05-19 10:22 +0000
  Re: Why would one use += 1 at the place of ++? David Lamb <dalamb@cs.queensu.ca> - 2011-05-19 06:40 -0400
    Re: Why would one use += 1 at the place of ++? Jeff Higgins <jeff@invalid.invalid> - 2011-05-19 07:58 -0400
    [OT] Re: Why would one use += 1 at the place of ++? Eric Sosman <esosman@ieee-dot-org.invalid> - 2011-05-19 08:03 -0400
      Re: [OT] Re: Why would one use += 1 at the place of ++? Patricia Shanahan <pats@acm.org> - 2011-05-19 07:35 -0700
        Re: [OT] Re: Why would one use += 1 at the place of ++? Eric Sosman <esosman@ieee-dot-org.invalid> - 2011-05-19 22:57 -0400
          Re: [OT] Re: Why would one use += 1 at the place of ++? rossum <rossum48@coldmail.com> - 2011-05-20 11:00 +0100
          Re: [OT] Re: Why would one use += 1 at the place of ++? Patricia Shanahan <pats@acm.org> - 2011-05-20 12:55 -0700
      Re: [OT] Re: Why would one use += 1 at the place of ++? David Lamb <dalamb@cs.queensu.ca> - 2011-05-19 17:58 -0400
        Re: [OT] Re: Why would one use += 1 at the place of ++? Eric Sosman <esosman@ieee-dot-org.invalid> - 2011-05-19 23:13 -0400
    Re: Why would one use += 1 at the place of ++? Lew <noone@lewscanon.com> - 2011-05-19 08:43 -0400
  Re: Why would one use += 1 at the place of ++? Eric Sosman <esosman@ieee-dot-org.invalid> - 2011-05-19 07:51 -0400
  Re: Why would one use += 1 at the place of ++? Jeff Higgins <jeff@invalid.invalid> - 2011-05-19 08:03 -0400
    Re: Why would one use += 1 at the place of ++? Lew <noone@lewscanon.com> - 2011-05-19 08:08 -0400
  Re: Why would one use += 1 at the place of ++? Roedy Green <see_website@mindprod.com.invalid> - 2011-05-19 10:23 -0700
    Re: Why would one use += 1 at the place of ++? Merciadri Luca <Luca.Merciadri@student.ulg.ac.be> - 2011-05-19 21:15 +0200
      Re: Why would one use += 1 at the place of ++? Lew <noone@lewscanon.com> - 2011-05-19 15:29 -0400

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