Re: fixed type (delta) in ada

[Simon Wright <simon@pogner.demon.co.uk>]

Nick Roberts <nickroberts@callnetuk.com> writes:

> Nap wrote:
> > 
> > does anyone know why mutiplication between fixed type in ada produce a
> > big round off error?
> > ...
> 
> Do you want the short answer or the long answer, Nap?
> 
> The short version of the long answer is: the 'small' chosen for the type
> 'money' will be a power of two (e.g. 1/128); 0.20 will therefore not
> have an exact representation when converted to the type 'money'; this
> inexact representation of 0.20 will therefore produce an inexact result
> after multiplication.
> 
> The short version of the short answer is: use a decimal type instead of
> a fixed type (example follows).
> 
>    type Money is delta 0.01 digits 11;
> 
> Problem solved.

Alternatively,

  Money_Small : constant := 0.01;
  type Money is delta Money_Small range 0.0..100_000_000.00;
  for Money'Small use Money_Small;

gives the expected result for the case in question.