On 06/12/2013 15:49, Gábor Csárdi wrote:
On Fri, Dec 6, 2013 at 10:42 AM, Prof Brian Ripley
<rip...@stats.ox.ac.uk> wrote:
On 06/12/2013 14:42, Gábor Csárdi wrote:
On Fri, Dec 6, 2013 at 9:38 AM, Duncan Murdoch <murdoch.dun...@gmail.com>
wrote:
On 06/12/2013 8:21 AM, Larissa Hauer wrote:
[...]
I would not assume that a 2D matrix in C doesn't have gaps in it between
the
rows. Let C treat it as a vector, and write a little macro that does the
indexing. For example,
#define INDEX(i,j) (i) + rows*(j)
I would make this
#define INDEX(i,j) ((i) + rows*(j))
just to be on the safe side.
And to be safer on a 64-bit platform
#define INDEX(i,j) ((i) + rows*(R_xlen_t)(j))
since rows*j might overflow there.
Indeed. Of course this still does not save you from indexing
out-of-range and integer overflow in the addition.
To a large extent it does. It means the arithmetic is done in R_xlen_t,
64-bit on 64-bit machines, and so any legitimate index gets computed
correctly.
Gabor
[...]
--
Brian D. Ripley, rip...@stats.ox.ac.uk
Professor of Applied Statistics, http://www.stats.ox.ac.uk/~ripley/
University of Oxford, Tel: +44 1865 272861 (self)
1 South Parks Road, +44 1865 272866 (PA)
Oxford OX1 3TG, UK Fax: +44 1865 272595
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