From mboxrd@z Thu Jan  1 00:00:00 1970
X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) on polar.synack.me
X-Spam-Level: 
X-Spam-Status: No, score=-1.9 required=5.0 tests=BAYES_00
	autolearn=unavailable autolearn_force=no version=3.4.4
Path: 
 eternal-september.org!reader01.eternal-september.org!reader02.eternal-september.org!feeder.eternal-september.org!news.swapon.de!fu-berlin.de!uni-berlin.de!individual.net!not-for-mail
From: Niklas Holsti <niklas.holsti@tidorum.invalid>
Newsgroups: comp.lang.ada
Subject: Re: Ada case-statement
Date: Thu, 15 Mar 2018 09:56:52 +0200
Organization: Tidorum Ltd
Message-ID: <fguna4Fb0ugU1@mid.individual.net>
References: <365d65ea-5f4b-4b6a-be9b-1bba146394ab@googlegroups.com>
 <p8bnbi$n0f$1@gioia.aioe.org> <p8cgeh$1v7d$1@gioia.aioe.org>
 <76eeca56-3246-49d2-baf3-0879741e7e12@googlegroups.com>
 <p8d1q1$jub$1@gioia.aioe.org>
Mime-Version: 1.0
Content-Type: text/plain; charset=utf-8; format=flowed
Content-Transfer-Encoding: 8bit
X-Trace: individual.net 7BcgSnA3qzZ6H6F6p9aStw9cGYMfCpJn2JqT5NcNWQv4apA3G2
Cancel-Lock: sha1:h8KtQCFT5mBsDSF72G/edq3kXjQ=
User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.8; rv:45.0)
 Gecko/20100101 Thunderbird/45.8.0
In-Reply-To: <p8d1q1$jub$1@gioia.aioe.org>
Xref: reader02.eternal-september.org comp.lang.ada:50988
Date: 2018-03-15T09:56:52+02:00
List-Id: <comp.lang.ada>

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
       .      @       .