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speed up bounds-checked element access and cache vector lengths #1511

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de977ea
speed up bounds-checked element access and cache vector lengths
kevinushey Sep 30, 2026
7946442
update NEWS
kevinushey Sep 30, 2026
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9 changes: 9 additions & 0 deletions ChangeLog
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Original file line number Diff line number Diff line change
@@ -1,3 +1,12 @@
2026-09-30 Kevin Ushey <kevinushey@gmail.com>

* inst/include/Rcpp/vector/traits.h: Move the out-of-bounds warning into
a cold, out-of-line helper; cache the vector length in proxy_cache
* inst/include/Rcpp/vector/Vector.h: Return the cached length from
size() and length() rather than calling Rf_xlength() each time
* inst/include/Rcpp/vector/Matrix.h: Cache the number of columns
* inst/include/Rcpp/vector/SubMatrix.h: Idem

2026-09-22 Iñaki Ucar <iucar@fedoraproject.org>

* inst/include/Rcpp/sugar/matrix/col.h: Fix Col constructor using ncol()
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3 changes: 3 additions & 0 deletions inst/NEWS.Rd
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Expand Up @@ -27,6 +27,9 @@
warnings (Iñaki in \ghpr{1508} closing \ghit{1497})
\item The \code{col} constructor now uses \code{nrow} in an
initialization (Iñaki in \ghpr{1509})
\item Bounds-checked element access is faster, and vector lengths and
matrix column counts are now cached (Kevin in \ghpr{1511} closing
\ghit{1510})
}
\item Changes in Rcpp Documentation:
\itemize{
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30 changes: 16 additions & 14 deletions inst/include/Rcpp/vector/Matrix.h
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Expand Up @@ -28,6 +28,7 @@ namespace Rcpp{
template <int RTYPE, template <class> class StoragePolicy = PreserveStorage >
class Matrix : public Vector<RTYPE, StoragePolicy>, public MatrixBase<RTYPE, true, Matrix<RTYPE,StoragePolicy> > {
int nrows ;
int ncols ;

public:
using Vector<RTYPE, StoragePolicy>::size; // disambiguate diamond pattern for g++-6 and later
Expand All @@ -49,33 +50,33 @@ class Matrix : public Vector<RTYPE, StoragePolicy>, public MatrixBase<RTYPE, tru
typedef typename VECTOR::Proxy Proxy ;
typedef typename VECTOR::const_Proxy const_Proxy ;

Matrix() : VECTOR(Dimension(0, 0)), nrows(0) {}
Matrix() : VECTOR(Dimension(0, 0)), nrows(0), ncols(0) {}

Matrix(SEXP x) : VECTOR(x), nrows( VECTOR::dims()[0] ) {}
Matrix(SEXP x) : VECTOR(x), nrows( VECTOR::dims()[0] ), ncols( VECTOR::dims()[1] ) {}

Matrix( const Dimension& dims) : VECTOR( Rf_allocMatrix( RTYPE, dims[0], dims[1] ) ), nrows(dims[0]) {
Matrix( const Dimension& dims) : VECTOR( Rf_allocMatrix( RTYPE, dims[0], dims[1] ) ), nrows(dims[0]), ncols(dims[1]) {
if( dims.size() != 2 ) throw not_a_matrix();
VECTOR::init() ;
}
Matrix( const int& nrows_, const int& ncols) : VECTOR( Dimension( nrows_, ncols ) ),
nrows(nrows_)
Matrix( const int& nrows_, const int& ncols_) : VECTOR( Dimension( nrows_, ncols_ ) ),
nrows(nrows_), ncols(ncols_)
{}

template <typename Iterator>
Matrix( const int& nrows_, const int& ncols, Iterator start ) :
VECTOR( start, start + (static_cast<R_xlen_t>(nrows_)*ncols) ),
nrows(nrows_)
Matrix( const int& nrows_, const int& ncols_, Iterator start ) :
VECTOR( start, start + (static_cast<R_xlen_t>(nrows_)*ncols_) ),
nrows(nrows_), ncols(ncols_)
{
VECTOR::attr( "dim" ) = Dimension( nrows, ncols ) ;
}

Matrix( const int& n) : VECTOR( Dimension( n, n ) ), nrows(n) {}
Matrix( const int& n) : VECTOR( Dimension( n, n ) ), nrows(n), ncols(n) {}


Matrix( const Matrix& other) : VECTOR( other.get__() ), nrows(other.nrows) {}
Matrix( const Matrix& other) : VECTOR( other.get__() ), nrows(other.nrows), ncols(other.ncols) {}

template <bool NA, typename MAT>
Matrix( const MatrixBase<RTYPE,NA,MAT>& other ) : VECTOR( Rf_allocMatrix( RTYPE, static_cast<int>(other.nrow()), static_cast<int>(other.ncol()) ) ), nrows(static_cast<int>(other.nrow())) {
Matrix( const MatrixBase<RTYPE,NA,MAT>& other ) : VECTOR( Rf_allocMatrix( RTYPE, static_cast<int>(other.nrow()), static_cast<int>(other.ncol()) ) ), nrows(static_cast<int>(other.nrow())), ncols(static_cast<int>(other.ncol())) {
import_matrix_expression<NA,MAT>( other, nrows, ncol() ) ;
}

Expand All @@ -86,20 +87,21 @@ class Matrix : public Vector<RTYPE, StoragePolicy>, public MatrixBase<RTYPE, tru
if( ! ::Rf_isMatrix(x) ) throw not_a_matrix();
VECTOR::set__( x ) ;
nrows = other.nrows ;
ncols = other.ncols ;
return *this ;
}
Matrix& operator=( const SubMatrix<RTYPE>& ) ;

explicit Matrix( const no_init_matrix& obj) : VECTOR(Rf_allocMatrix(RTYPE, obj.nrow(), obj.ncol())), nrows(obj.nrow()) {}
explicit Matrix( const no_init_matrix& obj) : VECTOR(Rf_allocMatrix(RTYPE, obj.nrow(), obj.ncol())), nrows(obj.nrow()), ncols(obj.ncol()) {}

inline int ncol() const {
return VECTOR::dims()[1];
return ncols ;
}
inline int nrow() const {
return nrows ;
}
inline int cols() const {
return VECTOR::dims()[1];
return ncols ;
}
inline int rows() const {
return nrows ;
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3 changes: 2 additions & 1 deletion inst/include/Rcpp/vector/SubMatrix.h
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Expand Up @@ -56,7 +56,7 @@ class SubMatrix : public Rcpp::MatrixBase< RTYPE, true, SubMatrix<RTYPE> > {
} ;

template <int RTYPE, template <class> class StoragePolicy >
Matrix<RTYPE,StoragePolicy>::Matrix( const SubMatrix<RTYPE>& sub ) : VECTOR( Rf_allocMatrix( RTYPE, sub.nrow(), sub.ncol() )), nrows(sub.nrow()) {
Matrix<RTYPE,StoragePolicy>::Matrix( const SubMatrix<RTYPE>& sub ) : VECTOR( Rf_allocMatrix( RTYPE, sub.nrow(), sub.ncol() )), nrows(sub.nrow()), ncols(sub.ncol()) {
int nc = sub.ncol() ;
iterator start = VECTOR::begin() ;
iterator rhs_it ;
Expand All @@ -73,6 +73,7 @@ Matrix<RTYPE,StoragePolicy>& Matrix<RTYPE,StoragePolicy>::operator=( const SubMa
int nc = sub.ncol(), nr = sub.nrow() ;
if( nc != nrow() || nr != ncol() ){
nrows = nr ;
ncols = nc ;
VECTOR::set__( Rf_allocMatrix( RTYPE, nr, nc ) ) ;
}
iterator start = VECTOR::begin() ;
Expand Down
6 changes: 3 additions & 3 deletions inst/include/Rcpp/vector/Vector.h
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Expand Up @@ -263,17 +263,17 @@ class Vector :
#endif

/**
* the length of the vector, uses Rf_xlength
* the length of the vector, as cached by update()
*/
inline R_xlen_t length() const {
return ::Rf_xlength( Storage::get__() ) ;
return cache.get_size() ;
}

/**
* alias of length
*/
inline R_xlen_t size() const {
return ::Rf_xlength( Storage::get__() ) ;
return cache.get_size() ;
}

/**
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24 changes: 19 additions & 5 deletions inst/include/Rcpp/vector/traits.h
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Expand Up @@ -24,6 +24,16 @@
namespace Rcpp{
namespace traits{

// Kept out of line and marked cold so that the (almost never taken)
// warning path doesn't bloat element access and block optimization of
// hot loops, e.g. in sugar expressions.
#if defined(__GNUC__)
__attribute__((noinline, cold))
#endif
inline void warn_index_out_of_bounds(R_xlen_t i, R_xlen_t size) {
warning("subscript out of bounds (index %s >= vector size %s)", i, size); // #nocov
}

template <int RTYPE, template <class> class StoragePolicy = PreserveStorage >
class r_vector_cache{
public:
Expand All @@ -38,11 +48,12 @@ namespace traits{

inline void update( const VECTOR& v ) {
start = ::Rcpp::internal::r_vector_start<RTYPE>(v) ;
size = v.size();
size = ::Rf_xlength(v.get__());
}

inline iterator get() const { return start; }
inline const_iterator get_const() const { return start; }
inline R_xlen_t get_size() const { return size; }

inline proxy ref() { check_index(0); return start[0] ;}
inline proxy ref(R_xlen_t i) { check_index(i); return start[i] ; }
Expand All @@ -55,7 +66,7 @@ namespace traits{
void check_index(R_xlen_t i) const {
#ifndef RCPP_NO_BOUNDS_CHECK
if (i >= size) {

@Enchufa2 Enchufa2 Sep 30, 2026

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Maybe the likely/unlikely macro technique used in the kernel helps too in these cases?

@Enchufa2 Enchufa2 Sep 30, 2026

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I see there are C++ attributes too, but that means C++20.

warning("subscript out of bounds (index %s >= vector size %s)", i, size); // #nocov
warn_index_out_of_bounds(i, size); // #nocov
}
#endif
}
Expand All @@ -73,13 +84,15 @@ namespace traits{
typedef typename r_vector_proxy<RTYPE, StoragePolicy>::type proxy ;
typedef typename r_vector_const_proxy<RTYPE, StoragePolicy>::type const_proxy ;

proxy_cache(): p(0){}
proxy_cache(): p(0), size(0){}
~proxy_cache(){}
void update( const VECTOR& v ){
p = const_cast<VECTOR*>(&v) ;
size = ::Rf_xlength(v.get__());
}
inline iterator get() const { return iterator( proxy(*p, 0 ) ) ;}
inline const_iterator get_const() const { return const_iterator( const_proxy(*p, 0) ) ; }
inline R_xlen_t get_size() const { return size; }

inline proxy ref() { check_index(0); return proxy(*p,0) ; }
inline proxy ref(R_xlen_t i) { check_index(i); return proxy(*p,i);}
Expand All @@ -89,11 +102,12 @@ namespace traits{

private:
VECTOR* p ;
R_xlen_t size ;

void check_index(R_xlen_t i) const {
#ifndef RCPP_NO_BOUNDS_CHECK
if (i >= p->size()) {
warning("subscript out of bounds (index %s >= vector size %s)", i, p->size()); // #nocov
if (i >= size) {
warn_index_out_of_bounds(i, size); // #nocov
}
#endif
}
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