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From: antispam@fricas.org (Waldek Hebisch)
Newsgroups: comp.lang.c
Subject: Re: Suggested method for returning a string from a C program?
Date: Sat, 22 Mar 2025 14:07:43 -0000 (UTC)
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Kaz Kylheku <643-408-1753@kylheku.com> wrote:
> On 2025-03-22, bart <bc@freeuk.com> wrote:
> 
>> The point is that there was usually a size exactly double the width of 
>> 'int', but it become less necessary when 'int' reached 64 bits.
> 
> Yes, because other than for masks of 128 bits, there isn't a whole
> lot of stuff you can *count* for which you need such large integers.
> 
> Money?
> 
> In an accounting system, if you use signed 64 bits for pennies, you can
> go to 9.2 x 10^16 dollars.

Actually, to do fast division of N-bit number by fixed N-bit number
one need 2N-bit multiplication.  Such divisions appear in base
convertions (to decimal) and when doing "decimal" rounding.
Also, converting between currencies needs extra accuracy.  So
_fast_ financial arithmetic may need rather large number of digits,
current tendecy is to allow up to 37 digits in intermediate quantities.

Note that 64-bit _result_ type means that 32-bit integers are
largest that can be multiplied exactly, that is very limiting.

> Large integers are needed for crypto and such, but then 128 isn't enough
> anyway.

Double word arthmetic is crucial if you want efficient high-level
implementation of multiple precision arithmetic.  So, 64-bit is
enough on 32-bit machines, 128-bit is needed on 64-bit machines
and hypotetical 128-bit machines would need 256-bit integer
type as a building block for efficient multiple precision
arithmetic.

-- 
                              Waldek Hebisch