Re: Ada case-statement

[Niklas Holsti <niklas.holsti@tidorum.invalid>]

On 18-03-15 07:54 , J-P. Rosen wrote:
> Le 15/03/2018 à 04:10, Dan'l Miller a écrit :
>> For dense case statements that utilize all or most of an enumerated
>> type's enumerated values, a jump table is the most likely on most
>> processors to achieve O(1) growth [instead of if-statement-based O(n)
>> growth, where n is the quantity of enumerated values in an enumerated
>> type].
> Long time ago, as I was working on Ada/ED, my shelf had a PHD thesis
> entirely on how to generate code for case statements. Various techniques
> depending on the number of values, the density of mentionned values in
> the subtype, etc.
>
> Of course, you had the if/elsif and plain jump table techniques, but
> also hashed jump tables, jump tables indexed by intervals, various mixes
> (if/elsif to eliminate sparse cases, then tables for the rest)...

And soon we will have processors with the "Mill" architecture, which can 
execute up to five conditional jumps in _parallel_, in each CPU cycle... 
brings a whole new set of possibilities for case-statement codde :-)

https://millcomputing.com/docs/switches/

BTW, the Mill architecture would be good at running Ada programs: very 
good at controlling the handling arithmetic errors, also good at 
subprogram calling, threading, emphasis on security (octet-granularity 
memory protection), etc. As a statically scehduled processor, it _could_ 
also be the only hope left for a powerful architecture with somewhat 
deterministic execution timing, for use in critical real-time systems, 
although the Mill developers currently do not describe it as a real-time 
processor.

-- 
Niklas Holsti
Tidorum Ltd
niklas holsti tidorum fi
       .      @       .