Re: Representation clauses and side-efects on STM32F411 ravenscar runtime

[Bob Duff <bobduff@theworld.com>]

Frédéric Praca <frederic.praca@free.fr> writes:

> Le Sun, 02 Aug 2015 15:54:50 -0400, Bob Duff a écrit :
>
>> "Jeffrey R. Carter" <spam.jrcarter.not@spam.not.acm.org> writes:
>> 
>>> On 08/02/2015 01:59 AM, Frédéric Praca wrote:
>>>> 
>>>>    type Mantissa is range 0 .. 2**12 - 1 with Size => 12;
>>>>    type Fraction is range 0 .. 2**4 - 1 with Size => 4;
>> 
>> Note that the Sizes will be 12 and 4 by default.
>> 
>>> Wouldn't modular types be better for these?
>> 
>> Why would you want wraparound arithmetic for these?  Seems like it would
>> just hide bugs.
>
> I fully agree. Mantissa and Fraction don't have to use wraparound 
> arithmetic. In fact, these two variables together represent a fixed point 
> type and the magic must be inside the functions which calculates these 
> variables according to the bus frequency and by the way must take care of 
> the carry and possible overflow.

Then would a fixed-point type work?

    type Baud_Rate is delta 1.0/16 range ...;
    for Baud_Rate'Small use 1.0/16;

- Bob