Re: Here come the 128-bit pointers

From	BGB <cr88192@gmail.com>
Newsgroups	comp.lang.c
Subject	Re: Here come the 128-bit pointers
Date	2022-01-26 15:35 -0600
Organization	A noiseless patient Spider
Message-ID	<ssseqb$717$1@dont-email.me> (permalink)
References	(2 earlier) <ssochk$t26$1@dont-email.me> <sspgoj$s5l$1@dont-email.me> <ssprrc$d8h$1@dont-email.me> <ssr1jb$nqj$1@dont-email.me> <sssabd$625$1@dont-email.me>

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On 1/26/2022 2:18 PM, Bart wrote:
> On 26/01/2022 08:43, Bonita Montero wrote:
>> I don't see any sense in logical or physical 128 bit pointers.
>> Imagine that memory-density could be shrinked up to 100 times,
>> so computers could be equipped with much more memory. But it
>> would be impossible have tolerable access-times with an amount
>> of memory in the upper margin of 64 bit (that's 16 billion
>> gigabytes).
>> So the only usage for me would be a larger address space to
>> accomodate larger memory-mapped files. But memory-mapped files
>> are slow anyway as they don't allow pipelined transfers from
>> the disk (except asynchronous read-ahead). An access-facility
>> like in a database-system which issues pipelined asynchronous
>> operations is much more efficient.
>> And have a look at the filesystems: although ZFS data-layout
>> allows 128 bit filesystems, its current implementation is
>> limited to 64 bit.
> 
> How often are you going to be working with a single file more than 2**64 
> bytes in size? (Equivalent to 16 million 1TB drives I think.)
> 
> Or perhaps you want to be able memory-map every file on every computer 
> in the world at the same time?
> 

I expect such large mmaps to be exceedingly unlikely.

> The various plans for 128 bits anyway don't appear to give that kind of 
> addressability. While those uses are so niche that a software solution 
> will work perfectly well. Bear in mind that fetching any data from a 
> file will be bigger overhead than having to use two 64-bit registers to 
> emulate such a pointer.
> 
> I think the chip makers are just desperately trying to find more uses 
> for wider GP registers.

Could be.

My preference (in my ISA) had been to use register pairs.

Handling 128-bit data as fixed pairs has both some of the same features 
as having separate registers (such as not having much of the register 
space being "wasted" for narrower values), but in other cases pairs can 
be treated by the hardware (and ISA) as if they were a single larger 
register (without as much cost and complexity as would be associated 
with using separately addressable register pairs).

So, for example: R3:R2, R5:R4, and R7:R6 can be treated as a 128-bit 
register, wheres, say: R6:R5 or R7:R2 or similar cannot...

Though, going the other way and trying to, say, allows for 128x 32-bit 
registers or similar, would have its own issues (doesn't make sense from 
a cost/benefit POV).

Granted, this is for an ISA that is doing everything with a single big 
register file (no separate FPU or SIMD registers).

Thread

Here come the 128-bit pointers scott@slp53.sl.home (Scott Lurndal) - 2022-01-24 18:12 +0000
  Re: Here come the 128-bit pointers Dan Purgert <dan@djph.net> - 2022-01-24 18:31 +0000
  Re: Here come the 128-bit pointers BGB <cr88192@gmail.com> - 2022-01-24 15:41 -0600
  Re: Here come the 128-bit pointers Bonita Montero <Bonita.Montero@gmail.com> - 2022-01-25 08:25 +0100
    Re: Here come the 128-bit pointers BGB <cr88192@gmail.com> - 2022-01-25 02:31 -0600
      Re: Here come the 128-bit pointers Öö Tiib <ootiib@hot.ee> - 2022-01-25 02:04 -0800
        Re: Here come the 128-bit pointers scott@slp53.sl.home (Scott Lurndal) - 2022-01-25 14:48 +0000
        Re: Here come the 128-bit pointers BGB <cr88192@gmail.com> - 2022-01-25 11:54 -0600
          Re: Here come the 128-bit pointers scott@slp53.sl.home (Scott Lurndal) - 2022-01-25 18:23 +0000
            Re: Here come the 128-bit pointers BGB <cr88192@gmail.com> - 2022-01-25 14:17 -0600
          Re: Here come the 128-bit pointers David Brown <david.brown@hesbynett.no> - 2022-01-26 09:36 +0100
            Re: Here come the 128-bit pointers Theo <theom+news@chiark.greenend.org.uk> - 2022-01-28 22:12 +0000
      Re: Here come the 128-bit pointers Bonita Montero <Bonita.Montero@gmail.com> - 2022-01-25 19:49 +0100
        Re: Here come the 128-bit pointers BGB <cr88192@gmail.com> - 2022-01-25 15:59 -0600
          Re: Here come the 128-bit pointers scott@slp53.sl.home (Scott Lurndal) - 2022-01-25 22:25 +0000
          Re: Here come the 128-bit pointers Bonita Montero <Bonita.Montero@gmail.com> - 2022-01-26 09:43 +0100
            Re: Here come the 128-bit pointers scott@slp53.sl.home (Scott Lurndal) - 2022-01-26 15:53 +0000
              Re: Here come the 128-bit pointers Bonita Montero <Bonita.Montero@gmail.com> - 2022-01-26 17:25 +0100
            Re: Here come the 128-bit pointers Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2022-01-26 08:34 -0800
              Re: Here come the 128-bit pointers Bonita Montero <Bonita.Montero@gmail.com> - 2022-01-26 17:57 +0100
              Re: Here come the 128-bit pointers Bart <bc@freeuk.com> - 2022-01-26 17:10 +0000
                Re: Here come the 128-bit pointers scott@slp53.sl.home (Scott Lurndal) - 2022-01-26 17:27 +0000
                Re: Here come the 128-bit pointers Bart <bc@freeuk.com> - 2022-01-26 17:41 +0000
                Re: Here come the 128-bit pointers scott@slp53.sl.home (Scott Lurndal) - 2022-01-26 18:05 +0000
                Re: Here come the 128-bit pointers Bart <bc@freeuk.com> - 2022-01-26 18:23 +0000
                Re: Here come the 128-bit pointers BGB <cr88192@gmail.com> - 2022-01-26 14:42 -0600
                Re: Here come the 128-bit pointers BGB <cr88192@gmail.com> - 2022-01-26 14:30 -0600
              Re: Here come the 128-bit pointers Mateusz Viste <mateusz@xyz.invalid> - 2022-01-26 19:36 +0100
                Re: Here come the 128-bit pointers scott@slp53.sl.home (Scott Lurndal) - 2022-01-26 18:52 +0000
            Re: Here come the 128-bit pointers tth <tth@none.invalid> - 2022-01-26 21:01 +0100
            Re: Here come the 128-bit pointers Bart <bc@freeuk.com> - 2022-01-26 20:18 +0000
              Re: Here come the 128-bit pointers BGB <cr88192@gmail.com> - 2022-01-26 15:35 -0600
                Re: Here come the 128-bit pointers scott@slp53.sl.home (Scott Lurndal) - 2022-01-26 21:50 +0000
                Re: Here come the 128-bit pointers BGB <cr88192@gmail.com> - 2022-01-26 20:34 -0600
                Re: Here come the 128-bit pointers Bart <bc@freeuk.com> - 2022-01-27 12:11 +0000
                Re: Here come the 128-bit pointers BGB <cr88192@gmail.com> - 2022-01-27 13:40 -0600
        Re: Here come the 128-bit pointers William Ahern <william@25thandClement.com> - 2022-01-27 13:28 -0800
  Re: Here come the 128-bit pointers Theo Markettos <theom+news@chiark.greenend.org.uk> - 2022-01-28 23:18 +0000

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