README.md

dcircshift

Perform a circular shift on a double-precision floating-point strided array in-place.

Usage

var dcircshift = require( '@stdlib/blas/ext/base/dcircshift' );

dcircshift( N, k, x, strideX )

Performs a circular shift on a double-precision floating-point strided array in-place.

var Float64Array = require( '@stdlib/array/float64' );

var x = new Float64Array( [ 1.0, 2.0, 3.0, 4.0, 5.0 ] );

dcircshift( x.length, 2, x, 1 );
// x => <Float64Array>[ 4.0, 5.0, 1.0, 2.0, 3.0 ]

The function has the following parameters:

• N: number of indexed elements.
• k: number of positions to shift.
• x: input Float64Array.
• strideX: stride length.

The N and stride parameters determine which elements in the strided array are accessed at runtime. For example, to circularly shift every other element:

var Float64Array = require( '@stdlib/array/float64' );

var x = new Float64Array( [ 1.0, 0.0, 2.0, 0.0, 3.0, 0.0, 4.0, 0.0 ] );

dcircshift( 4, 1, x, 2 );
// x => <Float64Array>[ 4.0, 0.0, 1.0, 0.0, 2.0, 0.0, 3.0, 0.0 ]

Note that indexing is relative to the first index. To introduce an offset, use typed array views.

var Float64Array = require( '@stdlib/array/float64' );

// Initial array...
var x0 = new Float64Array( [ 0.0, 1.0, 2.0, 3.0, 4.0, 5.0 ] );

// Create an offset view...
var x1 = new Float64Array( x0.buffer, x0.BYTES_PER_ELEMENT*1 ); // start at 2nd element

// Circularly shift elements in the view:
dcircshift( 5, 2, x1, 1 );
// x0 => <Float64Array>[ 0.0, 4.0, 5.0, 1.0, 2.0, 3.0 ]

dcircshift.ndarray( N, k, x, strideX, offsetX )

Performs a circular shift on a double-precision floating-point strided array in-place using alternative indexing semantics.

var Float64Array = require( '@stdlib/array/float64' );

var x = new Float64Array( [ 1.0, 2.0, 3.0, 4.0, 5.0 ] );

dcircshift.ndarray( x.length, 2, x, 1, 0 );
// x => <Float64Array>[ 4.0, 5.0, 1.0, 2.0, 3.0 ]

The function has the following additional parameters:

• offsetX: starting index.

While typed array views mandate a view offset based on the underlying buffer, the offset parameter supports indexing semantics based on a starting index. For example, to access only the last three elements of the strided array:

var Float64Array = require( '@stdlib/array/float64' );

var x = new Float64Array( [ 1.0, 2.0, 3.0, 4.0, 5.0, 6.0 ] );

dcircshift.ndarray( 3, 1, x, 1, x.length-3 );
// x => <Float64Array>[ 1.0, 2.0, 3.0, 6.0, 4.0, 5.0 ]

Notes

• If N <= 0, both functions return the strided array unchanged.
• If k is a multiple of N, both functions return the strided array unchanged.
• If k > 0 elements are shifted to the right.
• If k < 0 elements are shifted to the left.

Examples

var discreteUniform = require( '@stdlib/random/array/discrete-uniform' );
var dcircshift = require( '@stdlib/blas/ext/base/dcircshift' );

var x = discreteUniform( 10, -100, 100, {
    'dtype': 'float64'
});
console.log( x );

dcircshift( x.length, 3, x, 1 );
console.log( x );

---

C APIs

Usage

#include "stdlib/blas/ext/base/dcircshift.h"

stdlib_strided_dcircshift( N, k, *X, strideX )

Performs a circular shift on a double-precision floating-point strided array in-place.

double x[] = { 1.0, 2.0, 3.0, 4.0, 5.0 };

stdlib_strided_dcircshift( 5, 2, x, 1 );

The function accepts the following arguments:

• N: [in] CBLAS_INT number of indexed elements.
• k: [in] CBLAS_INT number of positions to shift.
• X: [inout] double* input array.
• strideX: [in] CBLAS_INT stride length.

void stdlib_strided_dcircshift( const CBLAS_INT N, const CBLAS_INT k, double *X, const CBLAS_INT strideX );

stdlib_strided_dcircshift_ndarray( N, k, *X, strideX, offsetX )

Performs a circular shift on a double-precision floating-point strided array in-place using alternative indexing semantics.

double x[] = { 1.0, 2.0, 3.0, 4.0, 5.0 };

stdlib_strided_dcircshift_ndarray( 5, 2, x, 1, 0 );

The function accepts the following arguments:

• N: [in] CBLAS_INT number of indexed elements.
• k: [in] CBLAS_INT number of positions to shift.
• X: [inout] double* input array.
• strideX: [in] CBLAS_INT stride length.
• offsetX: [in] CBLAS_INT starting index.

void stdlib_strided_dcircshift_ndarray( const CBLAS_INT N, const CBLAS_INT k, double *X, const CBLAS_INT strideX, const CBLAS_INT offsetX );

Examples

#include "stdlib/blas/ext/base/dcircshift.h"
#include <stdio.h>

int main( void ) {
    // Create a strided array:
    double x[] = { 1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0, 8.0 };

    // Specify the number of elements:
    const int N = 8;

    // Specify the shift amount:
    const int k = 3;

    // Specify a stride:
    const int strideX = 1;

    // Perform the circular shift:
    stdlib_strided_dcircshift( N, k, x, strideX );

    // Print the result:
    for ( int i = 0; i < 8; i++ ) {
        printf( "x[ %i ] = %lf\n", i, x[ i ] );
    }
}