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From: =?ISO-8859-1?Q?Santiago_Urue=F1a?= <suruena@gmail.com>
Newsgroups: comp.lang.ada
Subject: Re: and then... (a curiosity)
Date: Tue, 2 Sep 2008 15:34:20 -0700 (PDT)
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Date: 2008-09-02T15:34:20-07:00
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> I've noticed that. What is the justification for it? I presume that, bein=
g
> compiler writers, AdaCore has some specialized knowledge that led them to=
 make
> that choice.
>
I think that the idea is to always use "and then" / "or else" when
there is a function call because maybe thanks to lazy evaluation some
of those calls can be avoided. In contrast, the AdaCore style guide
suggest using plain "and" / "or" operators when just boolean flags are
involved because it is usually faster to evaluate all the variables
than using lazy evaluation.

Branches and jumps instructions really hurt performance in modern
processors, so when just a set of boolean variables must be evaluated
it is faster to read all of them instead of generating some branches.
When function calls are involved you will have those jump instructions
anyway, so it is better to use lazy evaluation to avoid the overhead
of the function call.

--
Santiago Urue=F1a-Pascual <suruena@gmail.com>