Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!mailrus!purdue!bu-cs!buengc!bph
From: bph@buengc.BU.EDU (Blair P. Houghton)
Newsgroups: comp.lang.c
Subject: Re: When is a cast not a cast?
Message-ID: <2918@buengc.BU.EDU>
Date: 19 May 89 18:08:41 GMT
References: <406@skye.ed.ac.uk> <10276@smoke.BRL.MIL> <2890@buengc.BU.EDU> <334.nlhp3@oracle.nl>
Reply-To: bph@buengc.bu.edu (Blair P. Houghton)
Followup-To: comp.lang.c
Organization: Boston Univ. Col. of Eng.
Lines: 50

In article <334.nlhp3@oracle.nl> bengsig@oracle.nl (Bjorn Engsig) writes:
>Pointer addition IS meaningless.

>Let's take an example of a 3 bit machine
>with only 0, 1, 2, ... , 7 as the only addresses.  Let's also declare

Urf.  Do I gotta say it again?  Yes.  I wish I could say it in double-
height, double-width, blinking, bold characters like I could if the
entire world had vt220 terminals, but, alas...

	POINTERS ARE NOT MEMORY LOCATIONS.  THAT'S A CHILDHOOD
	EXAMPLE FOR THE PASCAL-DEPROGRAMMED.  GROW UP, C-LAND 

(obligatory smiley for to mitigate the tone of that: :-).  Thanks.)

Simplest example:  you do pointer to int.  The compiler gets smart and
stores that particular int in an accumulator.  Now, tell me the address,
in octal big-endian...

>>It's one heck of an optimization if, for some reason, the subtraction
>>appears in a loop, and the addition does not.
>No, it probably would not be.  Since by the example above, it is seen
>that you would not be able to represent the pointer sum in a single word.

I can if it's not an overflow, and that's true of any form of computerized
arithmetic, so no problem.  What?  Are you going to take away my double-
precision multiplication just because it doesn't fit into a double?

See the rampant codepostings on overflow detection.

>In article <10276@smoke.BRL.MIL> gwyn@brl.arpa (Doug Gwyn) writes:
>>>Other postings have explained why we don't think a reasonable, consistent
>>>model for this feature is possible.
>True.

Irrelevant.  I don't think a reasonable, consistent model for the
universe is possible.  Does it collapse around us, therefore?

>BTW, what is the sum of the two 'pointers' earth *russia, *southamerica :
>58 45' 22" north, 43 45' 45" east
>and
>23 47' 19" south, 95 13' 18" west

what is the sum of
23 47' 19" south, 43 45' 45" east
and
4

				--Blair
				  "And you do that _daily_ in C..."