[FFmpeg-devel] [Issue 664] [PATCH] Fix AAC PNS Scaling

[Måns Rullgård]

Uoti Urpala <uoti.urpala at pp1.inet.fi> writes:

> On Tue, 2008-10-07 at 23:01 +0200, Michael Niedermayer wrote:
>> On Tue, Oct 07, 2008 at 04:40:20PM -0400, Alex Converse wrote:
>> > Does ffmpeg target any non IEEE-754 machines?
>> 
>> ffmpeg should work on mostly POSIX- mostly ISO C- twos complement machines
>> that does not implicate IEEE i think ...

The float to int conversion with magic bias assumes IEEE format
floats.  Most of the code seems rather insensitive to rounding modes
and such, though.

> Plain C says so little about floating point that it is impossible to
> write a useful program relying only on "guaranteed to work by the
> standard" assumptions. There's no widely used standard between the
> precision levels of C and IEEE-754, so in practice a program must choose
> between  1) require IEEE-754  2) list a custom set of assumptions  3)
> decide "how likely is this to work on practical platforms?" on a
> case-by-case basis.

Add the fact that many CPUs have a fast, not-quite-IEEE floating-point
mode.

-- 
M?ns Rullg?rd
mans at mansr.com