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From: anon@att.net
Newsgroups: comp.lang.ada
Subject: Re: evaluation of named numbers
Date: Sun, 17 Oct 2010 22:32:53 +0000 (UTC)
Organization: Aioe.org NNTP Server
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Date: 2010-10-17T22:32:53+00:00
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In <2304722c-027d-42f6-a45d-5a7646c35cf6@t8g2000yqk.googlegroups.com>, Rolf <rolf.ebert_nospam_@gmx.net> writes:
>I always thought that named numbers are fully evaluated with (almost)
>unlimited precision at compile time. I was quite astonished to see
>
>  Ticks : constant := 20 / 1000 * 16_000_000 / 8; -- 40_000 ticks
>
>evaluated to 0 and not to the expected 40.000. It seems that the
>compiler uses integer numbers also for intermediate results and 20 /
>1000 ends up to be 0 instead of 0.02. Any decent pocket calculator
>gets that right.
>
>The workaround is simple once I understood the problem:
>
>   Ticks : constant := 20 * 16_000_000 / 8 / 1000; --  40_000 ticks
>
>Are expressions for named numbers always evaluated left to right? I
>think I'll add an item to the review check list to always put
>multiplications on the left before any divisions.
>
>   Rolf


Since, Rm 4.5(8) states the Ada's answer to this problem but it 
solution in using parentheses will not corrent the problem so 
rewrite the equation may be needed.


  Ticks : constant := 20 * 16_000_000 / 8 / 1000 ; -- 40_000 ticks