Re: Re: About integer64

[Abramo Bagnara <abramo@alsa-project.org>]

Paul Davis wrote:
> 
> >What I'm misunderstanding? I tend to interpret the former and the latter
> >statements in a contradictory way.
> 
> my reading of the "docs" (the Mac OS X driver and utilities) is that
> RME haven't figured out a way to truncate the 64 bit fixed point
> representation to a 32 bit integer using the Xilinx FPGA. they have
> figured out how to render it as a 64 bit integer. so, they do the math
> using a fixed point representation, then transform to 64 bit integer
> when storing it in the register. the final part of the transform is
> done by the host CPU, in our case up in user space since we can't do
> float math conveniently in the kernel.
> 
> does that make it clearer?

Not very much:
a) if 32 bit integer could be enough expressive, what's the problem to
truncate it in your driver?
b) if a 32 bit integer is not enough and a float is preferrable:
considered that an ieee754 floating point is in the form (1+man)*2^exp
what's the problem in converting it in your driver using ffs and some
shift?

With both way I don't see the two point you make:
1) why bother with signed vs unsigned
2) why use 64 bit integer

Of course if a 64 bit integer is the best way to represent/report the
value all is fine, but in this case I doubt that you don't have
available the 64th bit for the sign.

-- 
Abramo Bagnara                       mailto:abramo@alsa-project.org

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It sounds good!

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