• The XS code part of xforms could be enhanced to analyse the supplied Perl parameters, and use the xform spec to determine the required type for each. It could then make ndarrays out of the Perl values with the required type, avoiding the need for conversion.
• A further benefit from that would be in generating versions of readdata (backward dataflow wouldn't make sense) that only processed Perl SVs, which would avoid overhead in the Perl-value-only scenario (and allow removing the PMCode for log10).

Other thoughts

• For generated redodims/readdata/writebackdata functions, they should merge the indx and either long or longlong case, since they are functionally identical and it's a bit less code to generate.
• non-[o] OtherPars should be copied into stack vars at the start of r/w functions, and be forced as rvalues.