Re: delta?

[Matthew Heaney <matthew_heaney@acm.org>]

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.