From: Jeffrey Carter <spam.jrcarter.not@spam.not.acm.org>
Subject: Re: RFC: Generic Fixed-Point IIR Filter
Date: Thu, 26 Mar 2015 15:02:18 -0700
Date: 2015-03-26T15:02:18-07:00 [thread overview]
Message-ID: <mf1vjn$23k$1@dont-email.me> (raw)
In-Reply-To: <mf1snt$3j6$1@loke.gir.dk>
On 03/26/2015 02:12 PM, Randy Brukardt wrote:
>
> Right. The rule specifically does not allow something like:
> A * B * C
> because that could take an infinite number of bits to evaluate (just keeping
> adding the * operators) - the number of bits needed is the sum of the
> maximum bits for each value. Universal-fixed is not supposed to overflow,
> some something has to make it implementable. In addition, most machines have
> a double precision multiply operation (like the 32*32 bits gives 64 bits
> operation the OP mentioned and a matching divide). So there's an obvious
> implementation in many cases (not on the margins, as I noted), so long as we
> are talking about a single multiply. Ada runtime math isn't supposed to
> require some complex infinite precision operation (which admittedly is
> interesting, since the compiler is required to do exactly that).
That makes sense. The main reason for fixed point in Ada 83 was to be faster
than SW floating-point on processors without FPUs. But since, as you note, the
compiler has to be able to do unbounded-precision math, then the compiler could
link in the library it uses to do that and do its intermediate calculations
using it. There could be a compiler switch to determine which is done. I think
GNAT has this.
What would be even better would be for the language to make the spec of that
unbounded-precision package part of the standard library.
--
Jeff Carter
"Since I strongly believe that overpopulation is by
far the greatest problem in the world, this [Soylent
Green] would be my only message movie."
Charleton Heston
123
next prev parent reply other threads:[~2015-03-26 22:02 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-03-26 16:25 RFC: Generic Fixed-Point IIR Filter Patrick Noffke
2015-03-26 17:05 ` Dmitry A. Kazakov
2015-03-26 17:41 ` Jeffrey Carter
2015-03-26 19:44 ` Patrick Noffke
2015-03-26 20:34 ` Randy Brukardt
2015-03-26 20:39 ` Jeffrey Carter
2015-03-26 21:12 ` Randy Brukardt
2015-03-26 21:30 ` Patrick Noffke
2015-03-26 22:02 ` Jeffrey Carter [this message]
2015-03-27 12:17 ` G.B.
2015-03-26 21:17 ` Patrick Noffke
2015-03-26 20:37 ` Jeffrey Carter
2015-03-27 11:37 ` Brian Drummond
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