linux-kernel - Re: Floating point usage inside kernel

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Fri, 25 Nov 2011 17:46:48 +0000
From:	Nuno Santos <nsantos@...gma.com>
To:	Paulo Marques <pmarques@...popie.com>
CC:	Jiri Slaby <jirislaby@...il.com>, linux-kernel@...r.kernel.org
Subject: Re: Floating point usage inside kernel

>
> 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
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/