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# ssorthp

> Sort a single-precision floating-point strided array using heapsort.

<section class="usage">

## Usage

```javascript
var ssorthp = require( '@stdlib/blas/ext/base/ssorthp' );
```

#### ssorthp( N, order, x, strideX )

Sorts a single-precision floating-point strided array using heapsort.

```javascript
var Float32Array = require( '@stdlib/array/float32' );

var x = new Float32Array( [ 1.0, -2.0, 3.0, -4.0 ] );

ssorthp( x.length, 1.0, x, 1 );
// x => <Float32Array>[ -4.0, -2.0, 1.0, 3.0 ]
```

The function has the following parameters:

-   **N**: number of indexed elements.
-   **order**: sort order. If `order < 0.0`, the input strided array is sorted in **decreasing** order. If `order > 0.0`, the input strided array is sorted in **increasing** order. If `order == 0.0`, the input strided array is left unchanged.
-   **x**: input [`Float32Array`][@stdlib/array/float32].
-   **strideX**: stride length.

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

```javascript
var Float32Array = require( '@stdlib/array/float32' );

var x = new Float32Array( [ 1.0, -2.0, 3.0, -4.0 ] );

ssorthp( 2, -1.0, x, 2 );
// x => <Float32Array>[ 3.0, -2.0, 1.0, -4.0 ]
```

Note that indexing is relative to the first index. To introduce an offset, use [`typed array`][mdn-typed-array] views.

```javascript
var Float32Array = require( '@stdlib/array/float32' );

// Initial array...
var x0 = new Float32Array( [ 1.0, 2.0, 3.0, 4.0 ] );

// Create an offset view...
var x1 = new Float32Array( x0.buffer, x0.BYTES_PER_ELEMENT*1 );

// Sort every other element...
ssorthp( 2, -1.0, x1, 2 );
// x0 => <Float32Array>[ 1.0, 4.0, 3.0, 2.0 ]
```

#### ssorthp.ndarray( N, order, x, strideX, offsetX )

Sorts a single-precision floating-point strided array using heapsort and alternative indexing semantics.

```javascript
var Float32Array = require( '@stdlib/array/float32' );

var x = new Float32Array( [ 1.0, -2.0, 3.0, -4.0 ] );

ssorthp.ndarray( x.length, 1.0, x, 1, 0 );
// x => <Float32Array>[ -4.0, -2.0, 1.0, 3.0 ]
```

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 three elements:

```javascript
var Float32Array = require( '@stdlib/array/float32' );

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

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

</section>

<!-- /.usage -->

<section class="notes">

## Notes

-   If `N <= 0` or `order == 0.0`, both functions return the strided array unchanged.
-   The algorithm distinguishes between `-0` and `+0`. When sorted in increasing order, `-0` is sorted before `+0`. When sorted in decreasing order, `-0` is sorted after `+0`.
-   The algorithm sorts `NaN` values to the end. When sorted in increasing order, `NaN` values are sorted last. When sorted in decreasing order, `NaN` values are sorted first.
-   The algorithm has space complexity `O(1)` and time complexity `O(N log2 N)`.
-   The algorithm is **unstable**, meaning that the algorithm may change the order of strided array elements which are equal or equivalent (e.g., `NaN` values).
-   The input strided array is sorted **in-place** (i.e., the input strided array is **mutated**).

</section>

<!-- /.notes -->

<section class="examples">

## Examples

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

```javascript
var discreteUniform = require( '@stdlib/random/array/discrete-uniform' );
var ssorthp = require( '@stdlib/blas/ext/base/ssorthp' );

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

ssorthp( x.length, -1.0, x, -1 );
console.log( x );
```

</section>

<!-- /.examples -->

* * *

<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/ssorthp.h"
```

#### stdlib_strided_ssorthp( N, order, \*X, strideX )

Sorts a single-precision floating-point strided array using heapsort.

```c
float x[] = { 1.0f, -2.0f, 3.0f, -4.0f };

stdlib_strided_ssorthp( 2, -1.0f, x, 1 );
```

The function accepts the following arguments:

-   **N**: `[in] CBLAS_INT` number of indexed elements.
-   **order**: `[in] float` sort order. If `order < 0.0`, the input strided array is sorted in **decreasing** order. If `order > 0.0`, the input strided array is sorted in **increasing** order. If `order == 0.0`, the input strided array is left unchanged.
-   **X**: `[inout] float*` input array.
-   **strideX**: `[in] CBLAS_INT` stride length.

```c
stdlib_strided_ssorthp( const CBLAS_INT N, const float order, float *X, const CBLAS_INT strideX );
```

<!--lint disable maximum-heading-length-->

#### stdlib_strided_ssorthp_ndarray( N, order, \*X, strideX, offsetX )

<!--lint enable maximum-heading-length-->

Sorts a single-precision floating-point strided array using heapsort and alternative indexing semantics.

```c
float x[] = { 1.0f, -2.0f, 3.0f, -4.0f };

stdlib_strided_ssorthp_ndarray( 4, 1.0f, x, 1, 0 );
```

The function accepts the following arguments:

-   **N**: `[in] CBLAS_INT` number of indexed elements.
-   **order**: `[in] float` sort order. If `order < 0.0`, the input strided array is sorted in **decreasing** order. If `order > 0.0`, the input strided array is sorted in **increasing** order. If `order == 0.0`, the input strided array is left unchanged.
-   **X**: `[inout] float*` input array.
-   **strideX**: `[in] CBLAS_INT` stride length.
-   **offsetX**: `[in] CBLAS_INT` starting index.

```c
stdlib_strided_ssorthp_ndarray( const CBLAS_INT N, const float order, float *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/ssorthp.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 };

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

    // Specify a stride:
    int strideX = 1;

    // Sort the array:
    stdlib_strided_ssorthp( N, 1.0f, x, strideX );

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

</section>

<!-- /.examples -->

</section>

<!-- /.c -->

<section class="references">

## References

-   Williams, John William Joseph. 1964. "Algorithm 232: Heapsort." _Communications of the ACM_ 7 (6). New York, NY, USA: Association for Computing Machinery: 347–49. doi:[10.1145/512274.512284][@williams:1964a].
-   Floyd, Robert W. 1964. "Algorithm 245: Treesort." _Communications of the ACM_ 7 (12). New York, NY, USA: Association for Computing Machinery: 701. doi:[10.1145/355588.365103][@floyd:1964a].

</section>

<!-- /.references -->

<!-- Section for related `stdlib` packages. Do not manually edit this section, as it is automatically populated. -->

<section class="related">

* * *

## See Also

-   <span class="package-name">[`@stdlib/blas/ext/base/dsorthp`][@stdlib/blas/ext/base/dsorthp]</span><span class="delimiter">: </span><span class="description">sort a double-precision floating-point strided array using heapsort.</span>
-   <span class="package-name">[`@stdlib/blas/ext/base/gsorthp`][@stdlib/blas/ext/base/gsorthp]</span><span class="delimiter">: </span><span class="description">sort a strided array using heapsort.</span>
-   <span class="package-name">[`@stdlib/blas/ext/base/ssort2hp`][@stdlib/blas/ext/base/ssort2hp]</span><span class="delimiter">: </span><span class="description">simultaneously sort two single-precision floating-point strided arrays based on the sort order of the first array using heapsort.</span>

</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/float32]: https://www.npmjs.com/package/@stdlib/array-float32

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

[@williams:1964a]: https://doi.org/10.1145/512274.512284

[@floyd:1964a]: https://doi.org/10.1145/355588.365103

<!-- <related-links> -->

[@stdlib/blas/ext/base/dsorthp]: https://github.com/stdlib-js/blas/tree/main/ext/base/dsorthp

[@stdlib/blas/ext/base/gsorthp]: https://github.com/stdlib-js/blas/tree/main/ext/base/gsorthp

[@stdlib/blas/ext/base/ssort2hp]: https://github.com/stdlib-js/blas/tree/main/ext/base/ssort2hp

<!-- </related-links> -->

</section>

<!-- /.links -->
