Path: utzoo!attcan!uunet!samsung!uakari.primate.wisc.edu!crdgw1!crdos1!davidsen
From: davidsen@crdos1.crd.ge.COM (Wm E Davidsen Jr)
Newsgroups: comp.arch
Subject: Re: MIPS, Compaq and Microsoft in bed - NYT story
Message-ID: <3188@crdos1.crd.ge.COM>
Date: 11 Feb 91 16:50:46 GMT
References: <29920@usc> <45758@mips.mips.COM>
Reply-To: davidsen@crdos1.crd.ge.com (bill davidsen)
Organization: GE Corp R&D Center, Schenectady NY
Lines: 43

In article <45758@mips.mips.COM> cprice@mips.COM (Charlie Price) writes:

| The important aspect of a 64-bit machine is that the user
| program virtual address space can be larger than 32 bits.
| If you want a nice flat big linear space to play with as you
| like, then you have to have big addresses.
| If you have big addresses, presumably you want to be able to
| manipulate them easily and that means same-sized registers
| and integer operations.

  What you are saying is that there are lots of poorly written
non-portable programs around which do bizarre non-portable things with
addresses, on the theory that because the {vax,sun,32k} has a linear
address space starting with zero, that "all that ANSI crap about pointers
doesn't mean much." (quote from one of my C students).

  Since all you can portable do in C is add or subtract ints and
pointers, or subtract pointers, you don't need the rest of the
arithmetic, except to do vastly unportable things. Portable programs
don't AND or XOR stuff into pointers, nor assume that their high or low
bits are available for flags.

  And honestly, other languages which have pointers are not usually used
to perform these atrocities. Other languages seem to be able to convince
programmers that a pointer is not an int.

  I really can't accept your idea that the size of an int must be the
same as the size of an address. I seem to remember a DG machine in which
the pointers were 48 bits, and several machines where the pointers are
not in the format of ordinal values of consecutively numbered bytes.
These machines exist and run, C and all the other usual languages.

  There is no particular technical reason not to have, say, 48 bit
addressing, with 32 bit ints. There may be marketing reasons, but that's
another issue completely.

  I agree that 64 bit ints are useful in solving certain problems, I
just don't buy the argument that useful work can't be done if the size
of int isn't the size of a pointer.
-- 
bill davidsen	(davidsen@crdos1.crd.GE.COM -or- uunet!crdgw1!crdos1!davidsen)
  "I'll come home in one of two ways, the big parade or in a body bag.
   I prefer the former but I'll take the latter" -Sgt Marco Rodrigez


Brought to you by Super Global Mega Corp .com