Re: Computer architects leaving Intel...

David Brown wrote:

On 14/09/2024 21:26, Thomas Koenig wrote:

MitchAlsup1 <mitchalsup@aol.com> schrieb:
>

In many cases int is slower now than long -- which violates the notion
of int from K&R days.

>
That's a designers's choice, I think.  It is possible to add 32-bit
instructions which should be as fast (or possibly faster) than
64-bit instructions, as AMD64 and ARM have shown.
>

 For some kinds of instructions, that's true - for others, it's not so easy without either making rather complicated instructions or having assembly instructions with undefined behaviour (imagine the terror that would bring to some people!).
 A classic example would be for "y = p[x++];" in a loop.  For a 64-bit type x, you would set up one register once with "p + x", and then have a load with post-increment instruction in the loop.  You can also do that with x as a 32-bit int, unless you are of the opinion that enough apples added to a pile should give a negative number of apples.  But with a wrapping type for x - such as unsigned int in C or modulo types in Ada, you have little choice but to hold "p" and "x" separately in registers, add them for every load, and do the increment and modulo operation.  I really can't see this all being handled by a single instruction.

This becomes much simpler in Rust where usize is the only legal index type:
Yeah, you have to actually write it as
   y = p[x];
   x += 1;
instead of a single line, but this makes zero difference to the compiler, right?
Terje
--
- <Terje.Mathisen at tmsw.no>
"almost all programming can be viewed as an exercise in caching"