Re: Behind the scenes of uniform arrays?

[Miroslav Silovic <silovic@zesoi.fer.hr>]

Jim Blandy <jimb@red-bean.com> writes:

> Yeah, there will always be a way for C code to get at the real bytes
> of a uniform array.  The SCM_CHARS macro works on uniform vectors,
> and SCM_VELTS works for uniform arrays.  I think.  :)

Hmm, let's see how much I remember of the internals (after writing
lots of uniform arrays code - and I still have to look at Guile
sources to do so).

SCM_LENGTH and SCM_VELTS return length and the first element of the
uniform vector. You probably want to cast the result of SCM_VELTS
(like (double*)SCM_VELTS(blah) )

SCM_ARRAY_V returns the uniform vector containing the elements of the
uniform array. SCM_ARRAY_NDIM is rank, SCM_ARRAY_BASE is the offset,
and SCM_ARRAY_DIMS is the vector with dimensions for the array. So
to index 2-dimensional array, you'd do

((double*)SCM_VELTS(SCM_ARRAY_V(arr))) + SCM_ARRAY_BASE(arr) + (i -
SCM_ARRAY_DIMS(a)[0].lbnd) * SCM_ARRAY_DIMS(a)[0].inc + (j -
SCM_ARRAY_DIMS(a)[1].lbnd) * SCM_ARRAY_DIMS(a)[1].inc

(result is a pointer to double).

This will work for both normal and shared arrays.

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