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332 changes: 332 additions & 0 deletions lib/node_modules/@stdlib/blas/ext/base/dlast-index-equal/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.

-->

# dlastIndexEqual

> Return the index of the last element in a double-precision floating-point strided array equal to a corresponding element in another strided array.

<!-- 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 -->

<!-- Package usage documentation. -->

<section class="usage">

## Usage

```javascript
var dlastIndexEqual = require( '@stdlib/blas/ext/base/dlast-index-equal' );
```

#### dlastIndexEqual( N, x, strideX, y, strideY )

Returns the index of the last element in a double-precision floating-point strided array equal to a corresponding element in another strided array.

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

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

var idx = dlastIndexEqual( x.length, x, 1, y, 1 );
// returns 2
```

The function has the following parameters:

- **N**: number of indexed elements.
- **x**: first input [`Float64Array`][@stdlib/array/float64].
- **strideX**: stride length for `x`.
- **y**: second input [`Float64Array`][@stdlib/array/float64].
- **strideY**: stride length for `y`.

If the function is unable to find matching elements, the function returns `-1`.

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

var x = new Float64Array( [ 1.0, 2.0, 3.0, 4.0 ] );
var y = new Float64Array( [ 5.0, 6.0, 7.0, 8.0 ] );

var idx = dlastIndexEqual( x.length, x, 1, y, 1 );
// returns -1
```

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

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

var x = new Float64Array( [ 1.0, 2.0, 3.0, 4.0, 5.0, 6.0 ] );
var y = new Float64Array( [ 0.0, 0.0, 3.0, 0.0, 0.0, 0.0 ] );

var idx = dlastIndexEqual( 3, x, 2, y, 2 );
// returns 1
```

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 ] );
var y0 = new Float64Array( [ 0.0, 0.0, 3.0, 0.0 ] );

// Create offset views...
var x1 = new Float64Array( x0.buffer, x0.BYTES_PER_ELEMENT*1 ); // start at 2nd element
var y1 = new Float64Array( y0.buffer, y0.BYTES_PER_ELEMENT*1 ); // start at 2nd element

// Find index...
var idx = dlastIndexEqual( 2, x1, 1, y1, 1 );
// returns 1
```

#### dlastIndexEqual.ndarray( N, x, strideX, offsetX, y, strideY, offsetY )

Returns the index of the last element in a double-precision floating-point strided array equal to a corresponding element in another strided array using alternative indexing semantics.

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

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

var idx = dlastIndexEqual.ndarray( x.length, x, 1, 0, y, 1, 0 );
// returns 2
```

The function has the following additional parameters:

- **offsetX**: starting index for `x`.
- **offsetY**: starting index for `y`.

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 each strided array:

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

var x = new Float64Array( [ 1.0, 2.0, 3.0, 4.0, 5.0, 6.0 ] );
var y = new Float64Array( [ 0.0, 0.0, 0.0, 4.0, 5.0, 6.0 ] );

var idx = dlastIndexEqual.ndarray( 3, x, 1, x.length-3, y, 1, y.length-3 );
// returns 2
```

</section>

<!-- /.usage -->

<!-- Package usage notes. Make sure to keep an empty line after the `section` element and another before the `/section` close. -->

<section class="notes">

## Notes

- When comparing elements, the function checks for equality using the strict equality operator `===`. As a consequence, `NaN` values are considered distinct, and `-0` and `+0` are considered the same.

</section>

<!-- /.notes -->

<!-- Package usage examples. -->

<section class="examples">

## Examples

<!-- eslint no-undef: "error" -->

```javascript
var Float64Array = require( '@stdlib/array/float64' );
var dlastIndexEqual = require( '@stdlib/blas/ext/base/dlast-index-equal' );

var x = new Float64Array( [ 1.0, 2.0, 3.0, 4.0, 5.0, 6.0 ] );
var y = new Float64Array( [ 0.0, 0.0, 3.0, 0.0, 0.0, 6.0 ] );

console.log( x );
console.log( y );

var idx = dlastIndexEqual.ndarray( x.length, x, 1, 0, y, 1, 0 );
console.log( idx );
```

</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/dlast_index_equal.h"
```

#### stdlib_strided_dlast_index_equal( N, \*X, strideX, \*Y, strideY )

Returns the index of the last element in a double-precision floating-point strided array equal to a corresponding element in another strided array.

```c
const double x[] = { 1.0, 2.0, 3.0, 4.0 };
const double y[] = { 0.0, 0.0, 3.0, 0.0 };

int idx = stdlib_strided_dlast_index_equal( 4, x, 1, y, 1 );
// returns 2
```

The function accepts the following arguments:

- **N**: `[in] CBLAS_INT` number of indexed elements.
- **X**: `[in] double*` first input array.
- **strideX**: `[in] CBLAS_INT` stride length for `X`.
- **Y**: `[in] double*` second input array.
- **strideY**: `[in] CBLAS_INT` stride length for `Y`.

```c
CBLAS_INT stdlib_strided_dlast_index_equal( const CBLAS_INT N, const double *X, const CBLAS_INT strideX, const double *Y, const CBLAS_INT strideY );
```

#### stdlib_strided_dlast_index_equal_ndarray( N, \*X, strideX, offsetX, \*Y, strideY, offsetY )

Returns the index of the last element in a double-precision floating-point strided array equal to a corresponding element in another strided array using alternative indexing semantics.

```c
const double x[] = { 1.0, 2.0, 3.0, 4.0 };
const double y[] = { 0.0, 0.0, 3.0, 0.0 };

int idx = stdlib_strided_dlast_index_equal_ndarray( 4, x, 1, 0, y, 1, 0 );
// returns 2
```

The function accepts the following arguments:

- **N**: `[in] CBLAS_INT` number of indexed elements.
- **X**: `[in] double*` first input array.
- **strideX**: `[in] CBLAS_INT` stride length for `X`.
- **offsetX**: `[in] CBLAS_INT` starting index for `X`.
- **Y**: `[in] double*` second input array.
- **strideY**: `[in] CBLAS_INT` stride length for `Y`.
- **offsetY**: `[in] CBLAS_INT` starting index for `Y`.

```c
CBLAS_INT stdlib_strided_dlast_index_equal_ndarray( const CBLAS_INT N, const double *X, const CBLAS_INT strideX, const CBLAS_INT offsetX, const double *Y, const CBLAS_INT strideY, const CBLAS_INT offsetY );
```

</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/dlast_index_equal.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 };
const double y[] = { 0.0, 0.0, 3.0, 0.0, 0.0, 6.0 };

// Specify the number of indexed elements:
const int N = 6;

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

// Perform the search:
int idx = stdlib_strided_dlast_index_equal( N, x, strideX, y, strideY );

// Print the result:
printf( "index value: %d\n", idx );
}
```

</section>

<!-- /.examples -->

</section>

<!-- /.c -->

<!-- Section to include cited references. If references are included, add a horizontal rule *before* the section. Make sure to keep an empty line after the `section` element and another before the `/section` close. -->

<section class="references">

</section>

<!-- /.references -->

<!-- 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

[mdn-typed-array]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray

</section>

<!-- /.links -->
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