[patch] Run-time external data access.

[Jules Bergmann]

Attach patch implements and tests external data access with run-time 
selection of the layout.

In theory, should work something like this:

	// Assume this is an operator() function for a class similar
	// to Fft.  It calls a backend (backend_) to do the work.
	// Since the backend is chosen at run-time (and is derived
	// from a virtual base class), we can't use the normal
	// Ext_data because it requires that layout be chosen
	// at compile-time.  Instead we need to use run-time ext_data.

	operator()(
	  const_Vector<T, Block0> in,
	  Vector<T, Block1> out)
	{

	  // First, determine layout of blocks:
	  Rt_layout<1> rtl_in  = block_layout(in.block());
	  Rt_layout<1> rtl_out = block_layout(out.block());

	  // Second, queury the backend about what layout
	  // it can support.
	  // Backend will modify rtl_in and rtl_out.
	  //
	  // For example, it might:
	  //  - set strides to unit-stride if it only supports
	  //    unit-stride,
	  //  - set complex formats to match,
	  //  - set dimension-ordering ,
	  //  - etc.
	  backend_->query_layout(rtl_in, rtl_out);

	  // Thrid, create run-time Ext_data objects
	  Rt_ext_data<Block0, 1> ext_in(in.block(), rtl_in);
	  Rt_ext_data<Block1, 1> ext_out(out.block(), rtl_out);

	  // Fourth, call functions in backend.
	  //
	  // Some knowledge may get encoded here.  In particular,
	  // because split- and interleaved- complex have
	  // different types, we need to call the appropriate
	  // backend function.  The backends could do this dispatch
	  // too.

	  // backends don't have functions with mixed split/interleaved
	  // arguments.
	  assert(rtl_in.complex == rtl_out.complex);
	  if (rtl_in.complex == cmplx_inter_fmt)
	  {
	    backend_->doit(rtl_in.data().as_inter(),
	                   rtl_in.stride(0),
	                   rtl_out.data().as_inter(),
	                   rtl_out.stride(0),
	                   out.size());
	  }
	  else // (rtl_in.complex == cmplx_split_fmt)
	  {
	    backend_->doit(rtl_in.data().as_split(),
	                   rtl_in.stride(0),
	                   rtl_out.data().as_split(),
	                   rtl_out.stride(0),
	                   out.size());
	  }
	}

				-- Jules

-- 
Jules Bergmann
CodeSourcery
jules at codesourcery.com
(650) 331-3385 x705
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