Re: Saturated Arithmetic

[Markus Kuhn <Markus.Kuhn@cl.cam.ac.uk>]

Mats Weber wrote:
> What is a saturating type ?

Saturated/saturating arithmetic is a variant of integer or
fixed-point arithmetic in which

  T'Last + 1 = T'Last
  T'First - 1 = T'First

etc., i.e. where overflows and underflows of computations
result in the closest representable value, and not in a
wraparound or exception.

Such types are *very* widely used in digital signal processing.
If your result in an audio filter algorithm happens to be
slightly above 16#ffff#, then the output you want is 16#ffff# as
the closest possible approximation to the real result and you
clearly do not want a wraparound to 16#0000# or an exception or
extra code that has to take care of this in inner loops.

Most DSPs as well as the new Intel MMX instructions provide
hardware support for saturated arithmetic. I guess, adding
saturated integer and fixed point types to Ada0X would be a sensible
idea (at least if there will be a digital signal processing
special annex).

Markus

-- 
Markus G. Kuhn, Security Group, Computer Lab, Cambridge University, UK
email: mkuhn at acm.org,  home page: <http://www.cl.cam.ac.uk/~mgk25/>