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From: Terje Mathisen <terje.mathisen@tmsw.no>
Newsgroups: comp.arch
Subject: Re: Segments
Date: Thu, 16 Jan 2025 10:11:36 +0100
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Thomas Koenig wrote:
> Keith Thompson <Keith.S.Thompson+u@gmail.com> schrieb:
>> Thomas Koenig <tkoenig@netcologne.de> writes:
>> [...]
>>> CHERY targets C, which on the one hand, I understand (there's a
>>> ton of C code out there), but trying to retrofit a safe memory
>>> model onto C seems a bit awkward - it might have been better to
>>> target a language which has arrays in the first place, unlike C.
>> [...]
>>
>> C does have arrays.
> 
> Sort of - they decay into pointers at first sight.
> 
> But what I should have written was "multi-dimensional arrays",
> with a reasonable way of handling them.
> 
Rust provides an interesting data point here:

It has Vec<> which is always implemented as a dope vector, i.e. a header 
which contains the starting point and current length, along with 
allocated size. For multidimendional work, the natural mapping is 
Vec<Vec<>>, i.e. similar to classic C arrays of arrays, but with 
boundary checking.

However, in my own testing I have found that it is often faster to 
flatten those multi-dim vectors, and instead use explicit multiplication 
to get the actual position:

   array[y][x] -> array[y*width + x]

Terje

-- 
- <Terje.Mathisen at tmsw.no>
"almost all programming can be viewed as an exercise in caching"