[Rd] suggestion how to use memcpy in duplicate.c

[Simon Urbanek]

On Apr 21, 2010, at 3:32 PM, Romain Francois wrote:

> Le 21/04/10 17:54, Matthew Dowle a écrit :
>> 
>>> From copyVector in duplicate.c :
>> 
>> void copyVector(SEXP s, SEXP t)
>> {
>>     int i, ns, nt;
>>     nt = LENGTH(t);
>>     ns = LENGTH(s);
>>     switch (TYPEOF(s)) {
>> ...
>>     case INTSXP:
>>     for (i = 0; i<  ns; i++)
>>         INTEGER(s)[i] = INTEGER(t)[i % nt];
>>     break;
>> ...
>> 
>> could that be replaced with :
>> 
>>     case INTSXP:
>>     for (i=0; i<ns/nt; i++)
>>         memcpy((char *)DATAPTR(s)+i*nt*sizeof(int), (char *)DATAPTR(t),
>> nt*sizeof(int));
>>     break;
> 
> or at least with something like this:
> 
> int* p_s = INTEGER(s) ;
> int* p_t = INTEGER(t) ;
> for( i=0 ; i < ns ; i++){
> 	p_s[i] = p_t[i % nt];
> }
> 
> since expanding the INTEGER macro over and over has a price.
> 

... in packages, yes, but not in core R.

Cheers,
Simon


>> and similar for the other types in copyVector.  This won't help regular
>> vector copies, since those seem to be done by the DUPLICATE_ATOMIC_VECTOR
>> macro, see next suggestion below, but it should help copyMatrix which calls
>> copyVector, scan.c which calls copyVector on three lines, dcf.c (once) and
>> dounzip.c (once).
>> 
>> For the DUPLICATE_ATOMIC_VECTOR macro there is already a comment next to it
>> :
>> 
>>     <FIXME>: surely memcpy would be faster here?
>> 
>> which seems to refer to the for loop  :
>> 
>>     else { \
>>     int __i__; \
>>     type *__fp__ = fun(from), *__tp__ = fun(to); \
>>     for (__i__ = 0; __i__<  __n__; __i__++) \
>>       __tp__[__i__] = __fp__[__i__]; \
>>   } \
>> 
>> Could that loop be replaced by the following ?
>> 
>>    else { \
>>    memcpy((char *)DATAPTR(to), (char *)DATAPTR(from), __n__*sizeof(type)); \
>>    }\
>> 
>> In the data.table package, dogroups.c uses this technique, so the principle
>> is tested and works well so far.
>> 
>> Are there any road blocks preventing this change, or is anyone already
>> working on it ?  If not then I'll try and test it (on Ubuntu 32bit) and
>> submit patch with timings, as before.  Comments/pointers much appreciated.
>> 
>> Matthew
>> 
>> ______________________________________________
>> R-devel at r-project.org mailing list
>> https://stat.ethz.ch/mailman/listinfo/r-devel
>> 
>> 
> 
> 
> -- 
> Romain Francois
> Professional R Enthusiast
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> http://romainfrancois.blog.free.fr
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