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From: Matthew Heaney <matthew_heaney@acm.org>
Subject: Re: delta?
Date: 1999/02/27
Message-ID: <m3btif32zy.fsf@mheaney.ni.net>#1/1
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Sender: matt@mheaney.ni.net
References: <7b9bl7$ki5$1@eng-ser1.erg.cuhk.edu.hk>
NNTP-Posting-Date: Sat, 27 Feb 1999 14:14:43 PDT
Newsgroups: comp.lang.ada
Date: 1999-02-27T00:00:00+00:00
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ycli6@se.cuhk.edu.hk (yukchi) writes:

> what is the meaning of delta and digits in the following sentence?
> type Money is delta 0.01 digits 15;

This is the declaration of a decimal fixed point type.  It means values
of Money as small as 1 cent are exactly representable.  Compare this to
a floating point type, which can only approximate the value of 1 cent.

You could do something like that using just plain fixed point types,
like this:


  Money_Delta : constant := 0.01;

  Money_First : constant := Integer'Pos (Integer'First) * Money_Delta;

  Money_Last : constant := Integer'Pos (Integer'Last) * Money_Delta;

  type Money is delta Money_Delta range Money_First .. Money_Last;

  for Money'Small use Money_Delta;


which gives you the range you can fit in an object with the same
precision as Integer.

BTW: The attribute T'Pos is handy here, because it allows you to convert
a static subtype to a univeral type, which you can then use in a
universal expression.