[vorbis-dev] mdct as hardware

[Monty]

On Wed, Mar 20, 2002 at 12:46:15AM +0100, Luis Azuara wrote:
> Hi vorbis-dev!
> 
> I'm working with Pattara in the oggonachip project, and wondering about
> the implementation of mdct.c as hardware. According your recomendations
> about using the floating point version, I would say, we have to implement
> the integerized
> version of mdct as a core, and use the fpu only to round the input
> values. By doing
> that, you think the result would be still acceptable?

You can use the MDCT in CVS as a fully fixed point implementation with
no problems *if* you have a 32bit*32bit->64bit multiply.  It's a
32*32->32 multiply (which is really 16*16->32) that is an issue.  One
of those things C only sort of provides.

Segher has magic code using a union of two 32 bit ints as a 64 bit
type that apparently newest versions of GCC will compile properly to
32*32->64 on platforms that have it.

Other than that, no real caveats in that code.

Monty

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