[FFmpeg-devel] [PATCH 02/14] libavcodec: Implementation of AAC_fixed_decoder (LC-module) [2/5]

Nedeljko Babic Nedeljko.Babic at imgtec.com
Wed Oct 8 11:46:56 CEST 2014

Hi again,

>> but I do agree that it is more maintainable to have one float emulation and I
>> am willing to integrate our emulation in softfloat.
>> However, there is a difference in some conventions used (for example is it more
>> important to represent exactly 0.5 or 1, order of fields in struct that
>> represents emulated float, etc.) and our aac implementation is tailored to use
>> our float emulation.
>i dont understand what you mean by 0.5 vs 1 ?
>floats are base 2 so both 0.5 and 1 can be represented exactly

I was a little unclear here, sorry.

It is true that both 0.5 and 1 can be represented exactly.

I was referring to a range of normalized mantissas.
We are using [0.5 - 1) and softfloat uses different range.
We do not have 1 in our range.

Please look at difference between av_normalize1_sf that is used in softfloat
version of mul and normalization used in our float_mul for example.

If we need to use range from softfloat, all calculations in aac fixed point 
implementation that depend on it need to be changed, so I am in favor of using
our range (of course :)), especially since softfloat is not being used anywhere
currently and changing the range of mantissas in it would not cause any
disturbance in ffmpeg.

- Nedeljko

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