Re: [Bluez-devel] more encoder stuff

[Lars Grunewaldt <lgw@dark-reality.de>]

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Marcel Holtmann wrote:
| Hi Henryk,
|
|
|>>The MAD library (www.underbit.com/products/mad/) is using fixed-point
|>>integer computation. Do you think it is possible to do the same thing
|>>for SBC? Will it give us some extra performance?
|>
|>Unfortunately I'm not familiar with fixed-point arithmetics, especially
|>with how to handle multiplication. So if anyone who has done this before
|>would step forward ...
|>
|>Well, I did some naive tests: I probably did something wrong, but I'm
|>not seeing any significant difference between floating point and fixed
|>point (that is: integer). For multiplication the difference is not
|>noticeable (1.38s vs. 1.36s in my test program) and for addition it is
|>not that big (0.77s vs. 0.47s).
|>
|>I guess we'll be fine using floating point as long as there is an FPU.
|
|
| we can optimize at any time if needed, because the SBC API should hide
| this stuff. For me this sounds perfect for a diploma thesis for someone
| interested in audio codec stuff and Bluetooth.

*raising hand*

thing is, on modern CPU you won't get much speedup with fixed point
stuff, because the main advantage was eliminated by Intel when they
build the pseudo-pipes into their FPU's. That's why id used floating
point operations for gfx for the first time, making life for non-Pentium
owners really hard. AMD also has the pseudo-pipes, and modern
multiplication/devision on FPU is very fast.

But of course there are still some cycles to kill in audio processing
always. I'll advertise this project to my professor...

cu,
~  Lars
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