feat: add blas/ext/base/zfill-nan

lib/node_modules/@stdlib/blas/ext/base/zfill-nan/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.
+
+-->
+
+# zfillNaN
+
+> Replace double-precision complex floating-point strided array elements equal to `NaN` with a specified scalar constant.
+
+<section class="usage">
+
+## Usage
+
+```javascript
+var zfillNaN = require( '@stdlib/blas/ext/base/zfill-nan' );
+```
+
+#### zfillNaN( N, alpha, x, strideX )
+
+Replaces double-precision complex floating-point strided array elements equal to `NaN` with a specified scalar constant.
+
+```javascript
+var Complex128Array = require( '@stdlib/array/complex128' );
+var Complex128 = require( '@stdlib/complex/float64/ctor' );
+
+var x = new Complex128Array( [ NaN, NaN, 3.0, 4.0, NaN, NaN, 7.0, 8.0 ] );
+
+var alpha = new Complex128( 5.0, 5.0 );
+
+zfillNaN( x.length, alpha, x, 1 );
+// x => <Complex128Array>[ 5.0, 5.0, 3.0, 4.0, 5.0, 5.0, 7.0, 8.0 ]
+```
+
+The function has the following parameters:
+
+-   **N**: number of indexed elements.
+-   **alpha**: scalar constant.
+-   **x**: input [`Complex128Array`][@stdlib/array/complex128].
+-   **strideX**: stride length.
+
+The `N` and stride parameters determine which elements in the strided array are accessed at runtime. For example, to iterate over every other element:
+
+```javascript
+var Complex128Array = require( '@stdlib/array/complex128' );
+var Complex128 = require( '@stdlib/complex/float64/ctor' );
+
+var x = new Complex128Array( [ NaN, NaN, 3.0, 4.0, NaN, NaN, 7.0, 8.0 ] );
+
+var alpha = new Complex128( 5.0, 5.0 );
+
+zfillNaN( 2, alpha, x, 2 );
+// x => <Complex128Array>[ 5.0, 5.0, 3.0, 4.0, 5.0, 5.0, 7.0, 8.0 ]
+```
+
+Note that indexing is relative to the first index. To introduce an offset, use [`typed array`][mdn-typed-array] views.
+
+```javascript
+var Complex128Array = require( '@stdlib/array/complex128' );
+var Complex128 = require( '@stdlib/complex/float64/ctor' );
+
+// Initial array:
+var x0 = new Complex128Array( [ 1.0, 2.0, NaN, NaN, 5.0, 6.0, NaN, NaN ] );
+
+// Create an offset view:
+var x1 = new Complex128Array( x0.buffer, x0.BYTES_PER_ELEMENT*1 ); // start at 2nd element
+
+// Define a scalar constant:
+var alpha = new Complex128( 5.0, 5.0 );
+
+// Replace every other NaN element:
+zfillNaN( 2, alpha, x1, 2 );
+// x0 => <Complex128Array>[ 1.0, 2.0, 5.0, 5.0, 5.0, 6.0, 5.0, 5.0 ]
+```
+
+#### zfillNaN.ndarray( N, alpha, x, strideX, offsetX )
+
+Replaces double-precision complex floating-point strided array elements equal to `NaN` with a specified scalar constant using alternative indexing semantics.
+
+```javascript
+var Complex128Array = require( '@stdlib/array/complex128' );
+var Complex128 = require( '@stdlib/complex/float64/ctor' );
+
+var x = new Complex128Array( [ NaN, NaN, 3.0, 4.0, NaN, NaN, 7.0, 8.0 ] );
+
+var alpha = new Complex128( 5.0, 5.0 );
+
+zfillNaN.ndarray( x.length, alpha, x, 1, 0 );
+// x => <Complex128Array>[ 5.0, 5.0, 3.0, 4.0, 5.0, 5.0, 7.0, 8.0 ]
+```
+
+The function has the following additional parameters:
+
+-   **offsetX**: starting index.
+
+While [`typed array`][mdn-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 two elements of the strided array:
+
+```javascript
+var Complex128Array = require( '@stdlib/array/complex128' );
+var Complex128 = require( '@stdlib/complex/float64/ctor' );
+
+var x = new Complex128Array( [ 1.0, 2.0, NaN, NaN, NaN, NaN ] );
+
+var alpha = new Complex128( 5.0, 5.0 );
+
+zfillNaN.ndarray( 2, alpha, x, 1, x.length-2 );
+// x => <Complex128Array>[ 1.0, 2.0, 5.0, 5.0, 5.0, 5.0 ]
+```
+
+</section>
+
+<!-- /.usage -->
+
+<section class="notes">
+
+## Notes
+
+-   If `N <= 0`, both functions return `x` unchanged.
+-   A complex number is considered `NaN` if either the real or imaginary component is `NaN`.
+
+</section>
+
+<!-- /.notes -->
+
+<section class="examples">
+
+## Examples
+
+<!-- eslint no-undef: "error" -->
+
+```javascript
+var nans = require( '@stdlib/array/nans' );
+var zfillNaN = require( '@stdlib/blas/ext/base/zfill-nan' );
+var Complex128 = require( '@stdlib/complex/float64/ctor' );
+
+var x = nans( 10, 'complex128' );
+console.log( x.get( 0 ).toString() );
+
+var alpha = new Complex128( 5.0, 5.0 );
+
+zfillNaN( x.length, alpha, x, 1 );
+console.log( x.get( 0 ).toString() );
+```
+
+</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/zfill_nan.h"
+```
+
+#### stdlib_strided_zfill_nan( N, alpha, \*X, strideX )
+
+Replaces double-precision complex floating-point strided array elements equal to `NaN` with a specified scalar constant.
+
+```c
+double x[] = { 1.0, 2.0, 0.0/0.0, 0.0/0.0, 5.0, 6.0, 0.0/0.0, 0.0/0.0 };
+const stdlib_complex128_t alpha = stdlib_complex128( 5.0, 5.0 );
+
+stdlib_strided_zfill_nan( 4, alpha, (stdlib_complex128_t *)x, 1 );
+```
+
+The function accepts the following arguments:
+
+-   **N**: `[in] CBLAS_INT` number of indexed elements.
+-   **alpha**: `[in] stdlib_complex128_t` scalar constant.
+-   **X**: `[inout] stdlib_complex128_t*` input array.
+-   **strideX**: `[in] CBLAS_INT` stride length.
+
+```c
+void stdlib_strided_zfill_nan( const CBLAS_INT N, const stdlib_complex128_t alpha, stdlib_complex128_t *X, const CBLAS_INT strideX );
+```
+
+#### stdlib_strided_zfill_nan_ndarray( N, alpha, \*X, strideX, offsetX )
+
+Replaces double-precision complex floating-point strided array elements equal to `NaN` with a specified scalar constant using alternative indexing semantics.
+
+```c
+double x[] = { 1.0, 2.0, 0.0/0.0, 0.0/0.0, 5.0, 6.0, 0.0/0.0, 0.0/0.0 };
+const stdlib_complex128_t alpha = stdlib_complex128( 5.0, 5.0 );
+
+stdlib_strided_zfill_nan_ndarray( 4, alpha, (stdlib_complex128_t *)x, 1, 0 );
+```
+
+The function accepts the following arguments:
+
+-   **N**: `[in] CBLAS_INT` number of indexed elements.
+-   **alpha**: `[in] stdlib_complex128_t` scalar constant.
+-   **X**: `[inout] stdlib_complex128_t*` input array.
+-   **strideX**: `[in] CBLAS_INT` stride length.
+-   **offsetX**: `[in] CBLAS_INT` starting index.
+
+```c
+void stdlib_strided_zfill_nan_ndarray( const CBLAS_INT N, const stdlib_complex128_t alpha, stdlib_complex128_t *X, const CBLAS_INT strideX, const CBLAS_INT offsetX );
+```
+
+</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/zfill_nan.h"
+#include "stdlib/complex/float64/ctor.h"
+#include <stdio.h>
+
+int main( void ) {
+    // Create a strided array of interleaved real and imaginary components:
+    double x[] = { 1.0, 2.0, 0.0/0.0, 0.0/0.0, 5.0, 6.0, 0.0/0.0, 0.0/0.0 };
+
+    // Create a scalar constant:
+    const stdlib_complex128_t alpha = stdlib_complex128( 5.0, 5.0 );
+
+    // Specify the number of elements:
+    const int N = 4;
+
+    // Specify a stride:
+    const int strideX = 1;
+
+    // Replace elements equal to `NaN`:
+    stdlib_strided_zfill_nan( N, alpha, (stdlib_complex128_t *)x, strideX );
+
+    // Print the result:
+    for ( int i = 0; i < 8; i++ ) {
+        printf( "x[ %i ] = %lf\n", i, x[ 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/complex128]: https://github.com/stdlib-js/stdlib/tree/develop/lib/node_modules/%40stdlib/array/complex128
+
+[mdn-typed-array]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray
+
+</section>
+
+<!-- /.links -->