public inbox for linux-kernel@vger.kernel.org
 help / color / mirror / Atom feed
From: Nuno Santos <nsantos@edigma.com>
To: Paulo Marques <pmarques@grupopie.com>
Cc: Jiri Slaby <jirislaby@gmail.com>, linux-kernel@vger.kernel.org
Subject: Re: Floating point usage inside kernel
Date: Fri, 25 Nov 2011 17:46:48 +0000	[thread overview]
Message-ID: <4ECFD488.4060805@edigma.com> (raw)
In-Reply-To: <4ECFCAD5.5040606@grupopie.com>

>
> Given the range of numbers you're working with, you can probably get
> away with just a 16.16 fixed point representation. The operations go
> like this:
>
> convert a double to a fixed point number just do (but not on the kernel):
>
>    fixed = (s32)(double * 65536.0);
>
> convert an integer to fixed:
>
>    fixed = integer<<  16;
>
> multiplication:
>
>    result = (s32)(((s64) fixed_a * fixed_b)>>  16);
>
> addition:
>
>    result = fixed_a + fixed_b;
>
> etc...
>
> Unless you have overflow or need more than 16 bits of fractional
> precision, you'll have no problem with this approach.
>
> I hope this helps,
Sorry, i'm not sure if I have completely understand your suggestion. Are 
you telling me to apply this transform only to my input data, or to all 
the operations that are applied in the function used in kernel?

Thanks,

With my best regards,

Nuno

  reply	other threads:[~2011-11-25 17:46 UTC|newest]

Thread overview: 9+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <S1754322Ab1KYK6W/20111125105822Z+929@vger.kernel.org>
2011-11-25 11:14 ` Floating point usage inside kernel Nuno Santos
2011-11-25 12:08   ` Jiri Slaby
2011-11-25 16:16     ` Nuno Santos
2011-11-25 17:05       ` Paulo Marques
2011-11-25 17:46         ` Nuno Santos [this message]
2011-11-25 18:10           ` Paulo Marques
2011-11-28 10:11             ` Nuno Santos
2011-11-28 12:50               ` Paulo Marques
2011-11-28  4:00       ` Andy Lutomirski

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=4ECFD488.4060805@edigma.com \
    --to=nsantos@edigma.com \
    --cc=jirislaby@gmail.com \
    --cc=linux-kernel@vger.kernel.org \
    --cc=pmarques@grupopie.com \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox