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feat: add blas/ext/base/smskrev
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‎lib/node_modules/@stdlib/blas/ext/base/smskrev/README.md‎

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<!--
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@license Apache-2.0
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Copyright (c) 2026 The Stdlib Authors.
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Licensed under the Apache License, Version 2.0 (the "License");
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you may not use this file except in compliance with the License.
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You may obtain a copy of the License at
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http://www.apache.org/licenses/LICENSE-2.0
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Unless required by applicable law or agreed to in writing, software
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distributed under the License is distributed on an "AS IS" BASIS,
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WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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See the License for the specific language governing permissions and
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limitations under the License.
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-->
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# smskrev
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> Reverse a single-precision floating-point strided array in-place according to a mask.
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<section class="usage">
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## Usage
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```javascript
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var smskrev = require( '@stdlib/blas/ext/base/smskrev' );
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```
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#### smskrev( N, x, strideX, mask, strideMask )
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Reverses a single-precision floating-point strided array `x` in-place according to a `mask`.
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```javascript
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var Float32Array = require( '@stdlib/array/float32' );
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var Uint8Array = require( '@stdlib/array/uint8' );
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var x = new Float32Array( [ -2.0, 1.0, 3.0, -5.0, 4.0, 0.0, -1.0, -3.0 ] );
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var mask = new Uint8Array( [ 0, 0, 0, 1, 0, 0, 0, 0 ] );
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smskrev( x.length, x, 1, mask, 1 );
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// x => <Float32Array>[ -3.0, -1.0, 0.0, -5.0, 4.0, 3.0, 1.0, -2.0 ]
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```
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The function has the following parameters:
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- **N**: number of indexed elements.
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- **x**: input [`Float32Array`][@stdlib/array/float32].
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- **strideX**: stride length for `x`.
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- **mask**: mask [`Uint8Array`][@stdlib/array/uint8]. If a `mask` array element is `0`, the corresponding element in `x` is considered unmasked and will participate in the reversal. If a `mask` array element is non-zero, the corresponding element in `x` is considered masked and the element will not participate in the reversal.
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- **strideMask**: stride length for `mask`.
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The `N` and stride parameters determine which elements in the strided arrays are accessed at runtime. For example, to reverse every other element:
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```javascript
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var Float32Array = require( '@stdlib/array/float32' );
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var Uint8Array = require( '@stdlib/array/uint8' );
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var x = new Float32Array( [ -2.0, 1.0, 3.0, -5.0, 4.0, 0.0 ] );
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var mask = new Uint8Array( [ 0, 0, 0, 0, 0, 0 ] );
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smskrev( 3, x, 2, mask, 2 );
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// x => <Float32Array>[ 4.0, 1.0, 3.0, -5.0, -2.0, 0.0 ]
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```
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Note that indexing is relative to the first index. To introduce an offset, use [`typed array`][mdn-typed-array] views.
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```javascript
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var Float32Array = require( '@stdlib/array/float32' );
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var Uint8Array = require( '@stdlib/array/uint8' );
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// Initial arrays...
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var x0 = new Float32Array( [ 1.0, -2.0, 3.0, -4.0, 5.0, -6.0 ] );
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var m0 = new Uint8Array( [ 0, 0, 0, 0, 0, 0 ] );
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// Create offset views...
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var x1 = new Float32Array( x0.buffer, x0.BYTES_PER_ELEMENT*1 ); // start at 2nd element
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var m1 = new Uint8Array( m0.buffer, m0.BYTES_PER_ELEMENT*1 );
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// Reverse every other element...
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smskrev( 3, x1, 2, m1, 2 );
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// x0 => <Float32Array>[ 1.0, -6.0, 3.0, -4.0, 5.0, -2.0 ]
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```
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#### smskrev.ndarray( N, x, strideX, offsetX, mask, strideMask, offsetMask )
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Reverses a single-precision floating-point strided array `x` in-place according to a `mask` and using alternative indexing semantics.
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```javascript
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var Float32Array = require( '@stdlib/array/float32' );
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var Uint8Array = require( '@stdlib/array/uint8' );
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var x = new Float32Array( [ -2.0, 1.0, 3.0, -5.0, 4.0, 0.0, -1.0, -3.0 ] );
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var mask = new Uint8Array( [ 0, 0, 0, 1, 0, 0, 0, 0 ] );
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smskrev.ndarray( x.length, x, 1, 0, mask, 1, 0 );
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// x => <Float32Array>[ -3.0, -1.0, 0.0, -5.0, 4.0, 3.0, 1.0, -2.0 ]
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```
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The function has the following additional parameters:
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- **offsetX**: starting index for `x`.
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- **offsetMask**: starting index for `mask`.
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While [`typed array`][mdn-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 of the strided array:
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```javascript
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var Float32Array = require( '@stdlib/array/float32' );
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var Uint8Array = require( '@stdlib/array/uint8' );
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var x = new Float32Array( [ 1.0, -2.0, 3.0, -4.0, 5.0, -6.0 ] );
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var mask = new Uint8Array( [ 0, 0, 0, 0, 0, 0 ] );
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smskrev.ndarray( 3, x, 1, x.length-3, mask, 1, mask.length-3 );
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// x => <Float32Array>[ 1.0, -2.0, 3.0, -6.0, 5.0, -4.0 ]
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```
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</section>
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<!-- /.usage -->
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<section class="notes">
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## Notes
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- If `N <= 0`, both functions return the strided array unchanged.
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- A swap is only performed when **both** elements in a pair are unmasked (i.e., their corresponding mask values are `0`). If either element is masked, neither element is modified.
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- 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.
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</section>
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<!-- /.notes -->
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<section class="examples">
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## Examples
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<!-- eslint no-undef: "error" -->
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```javascript
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var discreteUniform = require( '@stdlib/random/array/discrete-uniform' );
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var Uint8Array = require( '@stdlib/array/uint8' );
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var smskrev = require( '@stdlib/blas/ext/base/smskrev' );
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var x = discreteUniform( 10, -100, 100, {
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'dtype': 'float32'
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});
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console.log( x );
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var mask = new Uint8Array( [ 0, 0, 0, 1, 0, 0, 1, 0, 0, 0 ] );
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console.log( mask );
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smskrev( x.length, x, 1, mask, 1 );
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console.log( x );
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```
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</section>
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<!-- /.examples -->
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<!-- C interface documentation. -->
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* * *
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<section class="c">
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## C APIs
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<!-- Section to include introductory text. Make sure to keep an empty line after the intro `section` element and another before the `/section` close. -->
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<section class="intro">
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</section>
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<!-- /.intro -->
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<!-- C usage documentation. -->
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<section class="usage">
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### Usage
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```c
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#include "stdlib/blas/ext/base/smskrev.h"
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```
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#### stdlib_strided_smskrev( N, \*X, strideX, \*Mask, strideMask )
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Reverses a single-precision floating-point strided array `X` in-place according to a `Mask`.
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```c
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float x[] = { 1.0f, 2.0f, 3.0f, 4.0f };
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const uint8_t mask[] = { 0, 0, 0, 0 };
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stdlib_strided_smskrev( 4, x, 1, mask, 1 );
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```
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The function accepts the following arguments:
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- **N**: `[in] CBLAS_INT` number of indexed elements.
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- **X**: `[inout] float*` input array.
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- **strideX**: `[in] CBLAS_INT` stride length for `X`.
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- **Mask**: `[in] uint8_t*` mask array.
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- **strideMask**: `[in] CBLAS_INT` stride length for `Mask`.
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```c
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void stdlib_strided_smskrev( const CBLAS_INT N, float *X, const CBLAS_INT strideX, const uint8_t *Mask, const CBLAS_INT strideMask );
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```
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<!-- lint disable maximum-heading-length -->
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#### stdlib_strided_smskrev_ndarray( N, \*X, strideX, offsetX, \*Mask, strideMask, offsetMask )
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<!-- lint enable maximum-heading-length -->
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Reverses a single-precision floating-point strided array `X` in-place according to a `Mask` and using alternative indexing semantics.
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```c
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float x[] = { 1.0f, 2.0f, 3.0f, 4.0f };
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const uint8_t mask[] = { 0, 0, 0, 0 };
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stdlib_strided_smskrev_ndarray( 4, x, 1, 0, mask, 1, 0 );
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```
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The function accepts the following arguments:
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- **N**: `[in] CBLAS_INT` number of indexed elements.
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- **X**: `[inout] float*` input array.
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- **strideX**: `[in] CBLAS_INT` stride length for `X`.
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- **offsetX**: `[in] CBLAS_INT` starting index for `X`.
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- **Mask**: `[in] uint8_t*` mask array.
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- **strideMask**: `[in] CBLAS_INT` stride length for `Mask`.
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- **offsetMask**: `[in] CBLAS_INT` starting index for `Mask`.
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```c
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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 );
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```
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</section>
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<!-- /.usage -->
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<!-- C API usage notes. Make sure to keep an empty line after the `section` element and another before the `/section` close. -->
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<section class="notes">
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</section>
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<!-- /.notes -->
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<!-- C API usage examples. -->
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<section class="examples">
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### Examples
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```c
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#include "stdlib/blas/ext/base/smskrev.h"
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#include <stdint.h>
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#include <stdio.h>
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int main( void ) {
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// Create a strided array:
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float x[] = { 1.0f, -2.0f, 3.0f, -4.0f, 5.0f, -6.0f, 7.0f, -8.0f };
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// Create a mask array:
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const uint8_t mask[] = { 0, 0, 0, 1, 0, 0, 0, 0 };
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// Specify the number of elements:
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const int N = 8;
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// Specify strides:
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const int strideX = 1;
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const int strideMask = 1;
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// Reverse the array:
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stdlib_strided_smskrev( N, x, strideX, mask, strideMask );
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// Print the result:
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for ( int i = 0; i < 8; i++ ) {
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printf( "x[ %i ] = %f\n", i, x[ i ] );
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}
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}
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```
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</section>
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<!-- /.examples -->
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</section>
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<!-- /.c -->
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<!-- Section for related `stdlib` packages. Do not manually edit this section, as it is automatically populated. -->
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<section class="related">
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</section>
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<!-- /.related -->
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<!-- Section for all links. Make sure to keep an empty line after the `section` element and another before the `/section` close. -->
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<section class="links">
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[@stdlib/array/float32]: https://github.com/stdlib-js/stdlib/tree/develop/lib/node_modules/%40stdlib/array/float32
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[@stdlib/array/uint8]: https://github.com/stdlib-js/stdlib/tree/develop/lib/node_modules/%40stdlib/array/uint8
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[mdn-typed-array]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray
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<!-- <related-links> -->
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<!-- </related-links> -->
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</section>
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<!-- /.links -->

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