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smskrev

Reverse a single-precision floating-point strided array in-place according to a mask.

Installation

npm install @stdlib/blas-ext-base-smskrev

Alternatively,

• To load the package in a website via a script tag without installation and bundlers, use the ES Module available on the esm branch (see README).
• If you are using Deno, visit the deno branch (see README for usage intructions).
• For use in Observable, or in browser/node environments, use the Universal Module Definition (UMD) build available on the umd branch (see README).

The branches.md file summarizes the available branches and displays a diagram illustrating their relationships.

To view installation and usage instructions specific to each branch build, be sure to explicitly navigate to the respective README files on each branch, as linked to above.

Usage

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

smskrev( N, x, strideX, mask, strideMask )

Reverses a single-precision floating-point strided array in-place according to a mask.

var Float32Array = require( '@stdlib/array-float32' );
var Uint8Array = require( '@stdlib/array-uint8' );

var x = new Float32Array( [ -2.0, 1.0, 3.0, -5.0, 4.0, 0.0, -1.0, -3.0 ] );
var mask = new Uint8Array( [ 0, 0, 0, 1, 0, 0, 0, 0 ] );

smskrev( x.length, x, 1, mask, 1 );
// x => <Float32Array>[ -3.0, -1.0, 0.0, -5.0, 4.0, 3.0, 1.0, -2.0 ]

The function has the following parameters:

• N: number of indexed elements.
• x: input Float32Array.
• strideX: stride length for x.
• mask: mask Uint8Array. If a mask array element is 0, the corresponding element in x is considered valid and included in the reversal. If a mask array element is 1, the corresponding element in x is considered invalid/missing and excluded from the reversal.
• strideMask: stride length for mask.

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

var Float32Array = require( '@stdlib/array-float32' );
var Uint8Array = require( '@stdlib/array-uint8' );

var x = new Float32Array( [ -2.0, 1.0, 3.0, -5.0, 4.0, 0.0, -1.0, -3.0 ] );
var mask = new Uint8Array( [ 0, 0, 0, 0 ] );

smskrev( 4, x, 2, mask, 1 );
// x => <Float32Array>[ -1.0, 1.0, 4.0, -5.0, 3.0, 0.0, -2.0, -3.0 ]

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

var Float32Array = require( '@stdlib/array-float32' );
var Uint8Array = require( '@stdlib/array-uint8' );

// Initial arrays...
var x0 = new Float32Array( [ 1.0, -2.0, 3.0, -4.0, 5.0, -6.0 ] );
var m0 = new Uint8Array( [ 0, 0, 0, 0, 0, 0 ] );

// Create offset views...
var x1 = new Float32Array( x0.buffer, x0.BYTES_PER_ELEMENT*1 ); // start at 2nd element
var m1 = new Uint8Array( m0.buffer, m0.BYTES_PER_ELEMENT*1 );

// Reverse every other element...
smskrev( 3, x1, 2, m1, 1 );
// x0 => <Float32Array>[ 1.0, -6.0, 3.0, -4.0, 5.0, -2.0 ]

smskrev.ndarray( N, x, strideX, offsetX, mask, strideMask, offsetMask )

Reverses a single-precision floating-point strided array in-place according to a mask and using alternative indexing semantics.

var Float32Array = require( '@stdlib/array-float32' );
var Uint8Array = require( '@stdlib/array-uint8' );

var x = new Float32Array( [ -2.0, 1.0, 3.0, -5.0, 4.0, 0.0, -1.0, -3.0 ] );
var mask = new Uint8Array( [ 0, 0, 0, 1, 0, 0, 0, 0 ] );

smskrev.ndarray( x.length, x, 1, 0, mask, 1, 0 );
// x => <Float32Array>[ -3.0, -1.0, 0.0, -5.0, 4.0, 3.0, 1.0, -2.0 ]

The function has the following additional parameters:

• offsetX: starting index for x.
• offsetMask: starting index for mask.

While typed array views mandate a view offset based on the underlying buffer, the offset parameters support indexing semantics based on starting indices. For example, to access only the last three elements:

var Float32Array = require( '@stdlib/array-float32' );
var Uint8Array = require( '@stdlib/array-uint8' );

var x = new Float32Array( [ 1.0, -2.0, 3.0, -4.0, 5.0, -6.0 ] );
var mask = new Uint8Array( [ 0, 0, 0, 0, 0, 0 ] );

smskrev.ndarray( 3, x, 1, x.length-3, mask, 1, 3 );
// x => <Float32Array>[ 1.0, -2.0, 3.0, -6.0, 5.0, -4.0 ]

Notes

• If N <= 0, both functions return x unchanged.
• Where possible, one should "reverse" a strided array by negating its stride, which is an O(1) operation, in contrast to performing an in-place reversal, which is O(N). However, in certain circumstances, this is not tenable, particularly when interfacing with libraries which assume and/or expect a specific memory layout (e.g., strided array elements arranged in memory in ascending order). In general, when working with strided arrays, only perform an in-place reversal when strictly necessary.

Examples

var discreteUniform = require( '@stdlib/random-array-discrete-uniform' );
var Uint8Array = require( '@stdlib/array-uint8' );
var smskrev = require( '@stdlib/blas-ext-base-smskrev' );

var x = discreteUniform( 10, -100, 100, {
    'dtype': 'float32'
});
console.log( x );

var mask = new Uint8Array( [ 0, 0, 0, 1, 0, 0, 1, 0, 0, 0 ] );
console.log( mask );

smskrev( x.length, x, 1, mask, 1 );
console.log( x );

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C APIs

Usage

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

stdlib_strided_smskrev( N, *X, strideX, *Mask, strideMask )

Reverses a single-precision floating-point strided array in-place according to a mask.

#include <stdint.h>

float x[] = { 1.0f, 2.0f, 3.0f, 4.0f };
const uint8_t mask[] = { 0, 0, 0, 0 };

stdlib_strided_smskrev( 4, x, 1, mask, 1 );

The function accepts the following arguments:

• N: [in] CBLAS_INT number of indexed elements.
• X: [inout] float* input array.
• strideX: [in] CBLAS_INT stride length for X.
• Mask: [in] uint8_t* mask array.
• strideMask: [in] CBLAS_INT stride length for Mask.

void stdlib_strided_smskrev( const CBLAS_INT N, float *X, const CBLAS_INT strideX, const uint8_t *Mask, const CBLAS_INT strideMask );

stdlib_strided_smskrev_ndarray( N, *X, strideX, offsetX, *Mask, strideMask, offsetMask )

Reverses a single-precision floating-point strided array in-place according to a mask and using alternative indexing semantics.

#include <stdint.h>

float x[] = { 1.0f, 2.0f, 3.0f, 4.0f };
const uint8_t mask[] = { 0, 0, 0, 0 };

stdlib_strided_smskrev_ndarray( 4, x, 1, 0, mask, 1, 0 );

The function accepts the following arguments:

• N: [in] CBLAS_INT number of indexed elements.
• X: [inout] float* input array.
• strideX: [in] CBLAS_INT stride length for X.
• offsetX: [in] CBLAS_INT starting index for X.
• Mask: [in] uint8_t* mask array.
• strideMask: [in] CBLAS_INT stride length for Mask.
• offsetMask: [in] CBLAS_INT starting index for Mask.

void stdlib_strided_smskrev_ndarray( const CBLAS_INT N, float *X, const CBLAS_INT strideX, const CBLAS_INT offsetX, const uint8_t *Mask, const CBLAS_INT strideMask, const CBLAS_INT offsetMask );

Examples

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

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

    // Create a mask array:
    const uint8_t mask[] = { 0, 0, 0, 1, 0, 0, 0, 0 };

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

    // Specify strides:
    const int strideX = 1;
    const int strideMask = 1;

    // Reverse the array:
    stdlib_strided_smskrev( N, x, strideX, mask, strideMask );

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

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Notice

This package is part of stdlib, a standard library for JavaScript and Node.js, with an emphasis on numerical and scientific computing. The library provides a collection of robust, high performance libraries for mathematics, statistics, streams, utilities, and more.

For more information on the project, filing bug reports and feature requests, and guidance on how to develop stdlib, see the main project repository.

Community

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License

See LICENSE.

Copyright

Copyright © 2016-2026. The Stdlib Authors.