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

[Alex Converse]

On Tue, Oct 7, 2008 at 5:47 PM, M?ns Rullg?rd <mans at mansr.com> wrote:
> 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.
>

This chunk of code doesn't need rounding modes, it just needs the
internal representation. Though AAC-Main on the other hand...

--Alex