Re: [Bluez-devel] libsbc optimizing

[Brad Midgley <bmidgley@xmission.com>]

Henryk

> This doesn't particularly aid readability so I'd suggest to keep the old
> code in a comment

ok

> I thought about it: Do you have long integers on that platform or will
> they be slow too? Basically there should be no number greater than 2^16
> anywhere (I'll have to check that, though) and we only need add,
> multiply and shift. 

32-bit ints are not costly, but >32 probably are too expensive.

> A naive fixed point implementation would be to use a 32 bit integers and
> shift the original value left 16 bits (multiplying by 2^16) leaving 16
> bits before and 16 bits after the decimal point. Add and Shift will work
> as usual, but for multiply additional 16 bits (e.g. an integer type with
> at least 48 bits) are needed.

uclibc provides an fp emulation library that is already doing a naive 
implementation. On a 400mhz pxa255, it works (sort of) for a2dp sink but 
only if encoding parameters are set low. It doesn't work for a2dp 
source--it only produces some choppy audio and then drops out completely.

maybe we just need to break floats into two ints. using rationals 
(numerator/denominator) is what i was thinking when I saw that first fp 
division by bits[][].

Brad


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