feat: add blas/ext/base/dwapx

PR-URL: #12868
Reviewed-by: Athan Reines <kgryte@gmail.com>
Closes: stdlib-js/metr-issue-tracker#735

Author: anandkaranubc

lib/node_modules/@stdlib/blas/ext/base/dwapx/README.md

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+<!--
+
+@license Apache-2.0
+
+Copyright (c) 2026 The Stdlib Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+   http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+
+-->
+
+# dwapx
+
+> Add a scalar constant to each element in a double-precision floating-point strided array `x` and assign the results to elements in a double-precision floating-point strided array `w`.
+
+<section class="intro">
+
+This BLAS extension implements the operation
+
+<!-- <equation class="equation" label="eq:wapx" align="center" raw="\mathbf{w} = \mathbf{x} + \alpha" alt="Equation for wapx operation."> -->
+
+```math
+\mathbf{w} = \mathbf{x} + \alpha
+```
+
+<!-- </equation> -->
+
+This API is complementary to the package [`@stdlib/blas/ext/base/dapx`][@stdlib/blas/ext/base/dapx], which performs an in-place update.
+
+</section>
+
+<!-- /.intro -->
+
+<section class="usage">
+
+## Usage
+
+```javascript
+var dwapx = require( '@stdlib/blas/ext/base/dwapx' );
+```
+
+#### dwapx( N, alpha, x, strideX, w, strideW )
+
+Adds a scalar constant to each element in a double-precision floating-point strided array `x` and assigns the results to elements in a double-precision floating-point strided array `w`.
+
+```javascript
+var Float64Array = require( '@stdlib/array/float64' );
+
+var x = new Float64Array( [ 1.0, 2.0, 3.0, 4.0, 5.0 ] );
+var w = new Float64Array( [ 0.0, 0.0, 0.0, 0.0, 0.0 ] );
+
+dwapx( x.length, 5.0, x, 1, w, 1 );
+// w => <Float64Array>[ 6.0, 7.0, 8.0, 9.0, 10.0 ]
+```
+
+The function has the following parameters:
+
+-   **N**: number of indexed elements.
+-   **alpha**: scalar constant.
+-   **x**: input [`Float64Array`][@stdlib/array/float64].
+-   **strideX**: stride length for `x`.
+-   **w**: output [`Float64Array`][@stdlib/array/float64].
+-   **strideW**: stride length for `w`.
+
+The `N` and stride parameters determine which elements in the strided arrays are accessed at runtime. For example, to add `alpha` to every other element in `x` and assign the results to every other element in `w`:
+
+```javascript
+var Float64Array = require( '@stdlib/array/float64' );
+
+var x = new Float64Array( [ 1.0, 2.0, 3.0, 4.0, 5.0, 6.0 ] );
+var w = new Float64Array( [ 0.0, 0.0, 0.0, 0.0, 0.0, 0.0 ] );
+
+dwapx( 3, 5.0, x, 2, w, 2 );
+// w => <Float64Array>[ 6.0, 0.0, 8.0, 0.0, 10.0, 0.0 ]
+```
+
+Note that indexing is relative to the first index. To introduce an offset, use [`typed array`][mdn-typed-array] views.
+
+```javascript
+var Float64Array = require( '@stdlib/array/float64' );
+
+// Initial arrays...
+var x0 = new Float64Array( [ 1.0, 2.0, 3.0, 4.0, 5.0, 6.0 ] );
+var w0 = new Float64Array( [ 0.0, 0.0, 0.0, 0.0, 0.0, 0.0 ] );
+
+// Create offset views...
+var x1 = new Float64Array( x0.buffer, x0.BYTES_PER_ELEMENT*1 ); // start at 2nd element
+var w1 = new Float64Array( w0.buffer, w0.BYTES_PER_ELEMENT*2 ); // start at 3rd element
+
+dwapx( 3, 5.0, x1, 1, w1, 1 );
+// w0 => <Float64Array>[ 0.0, 0.0, 7.0, 8.0, 9.0, 0.0 ]
+```
+
+#### dwapx.ndarray( N, alpha, x, strideX, offsetX, w, strideW, offsetW )
+
+Adds a scalar constant to each element in a double-precision floating-point strided array `x` and assigns the results to elements in a double-precision floating-point strided array `w` using alternative indexing semantics.
+
+```javascript
+var Float64Array = require( '@stdlib/array/float64' );
+
+var x = new Float64Array( [ 1.0, 2.0, 3.0, 4.0, 5.0 ] );
+var w = new Float64Array( [ 0.0, 0.0, 0.0, 0.0, 0.0 ] );
+
+dwapx.ndarray( x.length, 5.0, x, 1, 0, w, 1, 0 );
+// w => <Float64Array>[ 6.0, 7.0, 8.0, 9.0, 10.0 ]
+```
+
+The function has the following additional parameters:
+
+-   **offsetX**: starting index for `x`.
+-   **offsetW**: starting index for `w`.
+
+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 add `alpha` to the last three elements of `x` and assign the results to the last three elements of `w`:
+
+```javascript
+var Float64Array = require( '@stdlib/array/float64' );
+
+var x = new Float64Array( [ 1.0, 2.0, 3.0, 4.0, 5.0 ] );
+var w = new Float64Array( [ 0.0, 0.0, 0.0, 0.0, 0.0 ] );
+
+dwapx.ndarray( 3, 5.0, x, 1, x.length-3, w, 1, w.length-3 );
+// w => <Float64Array>[ 0.0, 0.0, 8.0, 9.0, 10.0 ]
+```
+
+</section>
+
+<!-- /.usage -->
+
+<section class="notes">
+
+## Notes
+
+-   If `N <= 0`, both functions return `w` unchanged.
+
+</section>
+
+<!-- /.notes -->
+
+<section class="examples">
+
+## Examples
+
+<!-- eslint no-undef: "error" -->
+
+```javascript
+var discreteUniform = require( '@stdlib/random/array/discrete-uniform' );
+var dwapx = require( '@stdlib/blas/ext/base/dwapx' );
+
+var x = discreteUniform( 10, -100, 100, {
+    'dtype': 'float64'
+});
+console.log( x );
+
+var w = discreteUniform( 10, -100, 100, {
+    'dtype': 'float64'
+});
+console.log( w );
+
+dwapx( x.length, 5.0, x, 1, w, 1 );
+console.log( w );
+```
+
+</section>
+
+<!-- /.examples -->
+
+<!-- C interface documentation. -->
+
+* * *
+
+<section class="c">
+
+## C APIs
+
+<!-- Section to include introductory text. Make sure to keep an empty line after the intro `section` element and another before the `/section` close. -->
+
+<section class="intro">
+
+</section>
+
+<!-- /.intro -->
+
+<!-- C usage documentation. -->
+
+<section class="usage">
+
+### Usage
+
+```c
+#include "stdlib/blas/ext/base/dwapx.h"
+```
+
+#### stdlib_strided_dwapx( N, alpha, \*X, strideX, \*W, strideW )
+
+Adds a scalar constant to each element in a double-precision floating-point strided array `X` and assigns the results to elements in a double-precision floating-point strided array `W`.
+
+```c
+const double x[] = { 1.0, 2.0, 3.0, 4.0 };
+double w[] = { 0.0, 0.0, 0.0, 0.0 };
+
+stdlib_strided_dwapx( 4, 5.0, x, 1, w, 1 );
+```
+
+The function accepts the following arguments:
+
+-   **N**: `[in] CBLAS_INT` number of indexed elements.
+-   **alpha**: `[in] double` scalar constant.
+-   **X**: `[in] double*` input array.
+-   **strideX**: `[in] CBLAS_INT` stride length for `X`.
+-   **W**: `[out] double*` output array.
+-   **strideW**: `[in] CBLAS_INT` stride length for `W`.
+
+```c
+void stdlib_strided_dwapx( const CBLAS_INT N, const double alpha, const double *X, const CBLAS_INT strideX, double *W, const CBLAS_INT strideW );
+```
+
+<!-- lint disable maximum-heading-length -->
+
+#### stdlib_strided_dwapx_ndarray( N, alpha, \*X, strideX, offsetX, \*W, strideW, offsetW )
+
+<!-- lint enable maximum-heading-length -->
+
+Adds a scalar constant to each element in a double-precision floating-point strided array `X` and assigns the results to elements in a double-precision floating-point strided array `W` using alternative indexing semantics.
+
+```c
+const double x[] = { 1.0, 2.0, 3.0, 4.0 };
+double w[] = { 0.0, 0.0, 0.0, 0.0 };
+
+stdlib_strided_dwapx_ndarray( 4, 5.0, x, 1, 0, w, 1, 0 );
+```
+
+The function accepts the following arguments:
+
+-   **N**: `[in] CBLAS_INT` number of indexed elements.
+-   **alpha**: `[in] double` scalar constant.
+-   **X**: `[in] double*` input array.
+-   **strideX**: `[in] CBLAS_INT` stride length for `X`.
+-   **offsetX**: `[in] CBLAS_INT` starting index for `X`.
+-   **W**: `[out] double*` output array.
+-   **strideW**: `[in] CBLAS_INT` stride length for `W`.
+-   **offsetW**: `[in] CBLAS_INT` starting index for `W`.
+
+```c
+void stdlib_strided_dwapx_ndarray( const CBLAS_INT N, const double alpha, const double *X, const CBLAS_INT strideX, const CBLAS_INT offsetX, double *W, const CBLAS_INT strideW, const CBLAS_INT offsetW );
+```
+
+</section>
+
+<!-- /.usage -->
+
+<!-- C API usage notes. Make sure to keep an empty line after the `section` element and another before the `/section` close. -->
+
+<section class="notes">
+
+</section>
+
+<!-- /.notes -->
+
+<!-- C API usage examples. -->
+
+<section class="examples">
+
+### Examples
+
+```c
+#include "stdlib/blas/ext/base/dwapx.h"
+#include <stdio.h>
+
+int main( void ) {
+    // Create strided arrays:
+    const double x[] = { 1.0, -2.0, 3.0, -4.0, 5.0, -6.0, 7.0, -8.0 };
+    double w[] = { 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0 };
+
+    // Specify the number of indexed elements:
+    const int N = 8;
+
+    // Specify strides:
+    const int strideX = 1;
+    const int strideW = 1;
+
+    // Add a constant to each element in `x` and assign to `w`:
+    stdlib_strided_dwapx( N, 5.0, x, strideX, w, strideW );
+
+    // Print the result:
+    for ( int i = 0; i < 8; i++ ) {
+        printf( "w[ %i ] = %lf\n", i, w[ i ] );
+    }
+}
+```
+
+</section>
+
+<!-- /.examples -->
+
+</section>
+
+<!-- /.c -->
+
+<!-- Section for related `stdlib` packages. Do not manually edit this section, as it is automatically populated. -->
+
+<section class="related">
+
+</section>
+
+<!-- /.related -->
+
+<!-- Section for all links. Make sure to keep an empty line after the `section` element and another before the `/section` close. -->
+
+<section class="links">
+
+[@stdlib/array/float64]: https://github.com/stdlib-js/stdlib/tree/develop/lib/node_modules/%40stdlib/array/float64
+
+[@stdlib/blas/ext/base/dapx]: https://github.com/stdlib-js/stdlib/tree/develop/lib/node_modules/%40stdlib/blas/ext/base/dapx
+
+[mdn-typed-array]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray
+
+<!-- <related-links> -->
+
+<!-- </related-links> -->
+
+</section>
+
+<!-- /.links -->