Possible page inefficiency in do_matrix in array.c

In do_matrix in src/array.c there is a type switch containing :

case LGLSXP :
   for (i = 0; i < nr; i++)
   for (j = 0; j < nc; j++)
       LOGICAL(ans)[i + j * NR] = NA_LOGICAL;

That seems page inefficient, iiuc. Think it should be :

case LGLSXP :
   for (j = 0; j < nc; j++)
   for (i = 0; i < nr; i++)
       LOGICAL(ans)[i + j * NR] = NA_LOGICAL;

or more simply :

case LGLSXP :
   for (i = 0; i < nc*nr; i++)
       LOGICAL(ans)[i] = NA_LOGICAL;

( with some fine tuning required since NR is type R_xlen_t whilst i, nc
and nr are type int ).

Same goes for all the other types in that switch.

This came up on Stack Overflow here :
http://stackoverflow.com/questions/12220128/reason-for-faster-matrix-allocation-in-r

That is completely irrelevant - modern compilers will optimize the loops accordingly and there is no difference in speed. If you don't believe it, run benchmarks ;)

original
microbenchmark(matrix(nrow=10000, ncol=9999), times=10)
Unit: milliseconds
                               expr      min       lq  median       uq      max
1 matrix(nrow = 10000, ncol = 9999) 940.5519 940.6644 941.136 954.7196 1409.901

swapped
microbenchmark(matrix(nrow=10000, ncol=9999), times=10)
Unit: milliseconds
                               expr      min       lq   median      uq      max
1 matrix(nrow = 10000, ncol = 9999) 949.9638 950.6642 952.7497 961.001 1246.573

Cheers,
Simon
Matthew

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Possible page inefficiency in do_matrix in array.c

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