time-to-botec/squiggle/node_modules/@stdlib/strided/base/smskmap/README.md

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

# smskmap

> Apply a unary function accepting and returning single-precision floating-point numbers to each element in a single-precision floating-point strided input array according to a corresponding element in a strided mask array and assign each result to an element in a single-precision floating-point strided output array.

<section class="intro">

</section>

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<section class="usage">

## Usage

```javascript
var smskmap = require( '@stdlib/strided/base/smskmap' );
```

#### smskmap( N, x, strideX, mask, strideMask, y, strideY, fcn )

Applies a unary function accepting and returning single-precision floating-point numbers to each element in a single-precision floating-point strided input array according to a corresponding element in a strided mask array and assigns each result to an element in a single-precision floating-point strided output array.

```javascript
var Float32Array = require( '@stdlib/array/float32' );
var Uint8Array = require( '@stdlib/array/uint8' );
var absf = require( '@stdlib/math/base/special/absf' );

var x = new Float32Array( [ -2.0, 1.0, -3.0, -5.0, 4.0, 0.0, -1.0, -3.0 ] );
var m = new Uint8Array( [ 0, 0, 1, 0, 0, 1, 1, 0 ] );

// Compute the absolute values in-place:
smskmap( x.length, x, 1, m, 1, x, 1, absf );
// x => <Float32Array>[ 2.0, 1.0, -3.0, 5.0, 4.0, 0.0, -1.0, 3.0 ]
```

The function accepts the following arguments:

-   **N**: number of indexed elements.
-   **x**: input [`Float32Array`][@stdlib/array/float32].
-   **strideX**: index increment for `x`.
-   **mask**: mask [`Uint8Array`][@stdlib/array/uint8].
-   **strideMask**: index increment for `mask`.
-   **y**: output [`Float32Array`][@stdlib/array/float32].
-   **strideY**: index increment for `y`.
-   **fcn**: function to apply.

The `N` and `stride` parameters determine which elements in the strided arrays are accessed at runtime. For example, to index every other value in `x` and to index the first `N` elements of `y` in reverse order,

```javascript
var Float32Array = require( '@stdlib/array/float32' );
var Uint8Array = require( '@stdlib/array/uint8' );
var floor = require( '@stdlib/math/base/special/floor' );
var absf = require( '@stdlib/math/base/special/absf' );

var x = new Float32Array( [ -1.0, -2.0, -3.0, -4.0, -5.0, -6.0 ] );
var m = new Uint8Array( [ 0, 0, 1, 0, 0, 1 ] );
var y = new Float32Array( [ 0.0, 0.0, 0.0, 0.0, 0.0, 0.0 ] );

var N = floor( x.length / 2 );

smskmap( N, x, 2, m, 2, y, -1, absf );
// y => <Float32Array>[ 5.0, 0.0, 1.0, 0.0, 0.0, 0.0 ]
```

Note that indexing is relative to the first index. To introduce an offset, use [`typed array`][@stdlib/array/float32] views.

```javascript
var Float32Array = require( '@stdlib/array/float32' );
var Uint8Array = require( '@stdlib/array/uint8' );
var floor = require( '@stdlib/math/base/special/floor' );
var absf = require( '@stdlib/math/base/special/absf' );

// Initial arrays...
var x0 = new Float32Array( [ -1.0, -2.0, -3.0, -4.0, -5.0, -6.0 ] );
var m0 = new Uint8Array( [ 0, 0, 1, 0, 0, 1 ] );
var y0 = new Float32Array( [ 0.0, 0.0, 0.0, 0.0, 0.0, 0.0 ] );

// Create offset views...
var x1 = new Float32Array( x0.buffer, x0.BYTES_PER_ELEMENT*1 ); // start at 2nd element
var m1 = new Uint8Array( m0.buffer, m0.BYTES_PER_ELEMENT*3 ); // start at 4th element
var y1 = new Float32Array( y0.buffer, y0.BYTES_PER_ELEMENT*3 ); // start at 4th element

var N = floor( x0.length / 2 );

smskmap( N, x1, -2, m1, 1, y1, 1, absf );
// y0 => <Float32Array>[ 0.0, 0.0, 0.0, 6.0, 4.0, 0.0 ]
```

#### smskmap.ndarray( N, x, strideX, offsetX, mask, strideMask, offsetMask, y, strideY, offsetY, fcn )

Applies a unary function accepting and returning single-precision floating-point numbers to each element in a single-precision floating-point strided input array according to a corresponding element in a strided mask array and assigns each result to an element in a single-precision floating-point strided output array using alternative indexing semantics.

```javascript
var Float32Array = require( '@stdlib/array/float32' );
var Uint8Array = require( '@stdlib/array/uint8' );
var absf = require( '@stdlib/math/base/special/absf' );

var x = new Float32Array( [ -1.0, -2.0, -3.0, -4.0, -5.0 ] );
var m = new Uint8Array( [ 0, 0, 1, 0, 0 ] );
var y = new Float32Array( [ 0.0, 0.0, 0.0, 0.0, 0.0 ] );

smskmap.ndarray( x.length, x, 1, 0, m, 1, 0, y, 1, 0, absf );
// y => <Float32Array>[ 1.0, 2.0, 0.0, 4.0, 5.0 ]
```

The function accepts the following additional arguments:

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

While [`typed array`][@stdlib/array/float32] views mandate a view offset based on the underlying `buffer`, the `offsetX` and `offsetY` parameters support indexing semantics based on starting indices. For example, to index every other value in `x` starting from the second value and to index the last `N` elements in `y`,

```javascript
var Float32Array = require( '@stdlib/array/float32' );
var Uint8Array = require( '@stdlib/array/uint8' );
var floor = require( '@stdlib/math/base/special/floor' );
var absf = require( '@stdlib/math/base/special/absf' );

var x = new Float32Array( [ -1.0, -2.0, -3.0, -4.0, -5.0, -6.0 ] );
var m = new Uint8Array( [ 0, 0, 1, 0, 0, 1 ] );
var y = new Float32Array( [ 0.0, 0.0, 0.0, 0.0, 0.0, 0.0 ] );

var N = floor( x.length / 2 );

smskmap.ndarray( N, x, 2, 1, m, 2, 1, y, -1, y.length-1, absf );
// y => <Float32Array>[ 0.0, 0.0, 0.0, 0.0, 4.0, 2.0 ]
```

</section>

<!-- /.usage -->

<section class="notes">

</section>

<!-- /.notes -->

<section class="examples">

## Examples

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

```javascript
var round = require( '@stdlib/math/base/special/round' );
var randu = require( '@stdlib/random/base/randu' );
var bernoulli = require( '@stdlib/random/base/bernoulli' );
var Float32Array = require( '@stdlib/array/float32' );
var Uint8Array = require( '@stdlib/array/uint8' );
var smskmap = require( '@stdlib/strided/base/smskmap' );

function scale( x ) {
    return x * 10.0;
}

var x = new Float32Array( 10 );
var m = new Uint8Array( x.length );
var y = new Float32Array( x.length );

var i;
for ( i = 0; i < x.length; i++ ) {
    x[ i ] = round( (randu()*200.0) - 100.0 );
    m[ i ] = bernoulli( 0.2 );
}
console.log( x );
console.log( m );
console.log( y );

smskmap.ndarray( x.length, x, 1, 0, m, 1, 0, y, -1, y.length-1, scale );
console.log( y );
```

</section>

<!-- /.examples -->

<!-- C interface documentation. -->

* * *

<section class="c">

## C APIs

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<section class="intro">

</section>

<!-- /.intro -->

<!-- C usage documentation. -->

<section class="usage">

### Usage

```c
#include "stdlib/strided/base/smskmap.h"
```

#### stdlib_strided_smskmap( N, \*X, strideX, \*Mask, strideMask, \*Y, strideY, fcn )

Applies a unary function accepting and returning single-precision floating-point numbers to each element in a single-precision floating-point strided input array according to a corresponding element in a strided mask array and assigns each result to an element in a single-precision floating-point strided output array.

```c
#include <stdint.h>

static float scale( const float x ) {
    return x * 10.0f;
}

float X[] = { 1.0f, 2.0f, 3.0f, 4.0f, 5.0f, 6.0f };
uint8_t M[] = { 0, 0, 1, 0, 0, 1 };
float Y[] = { 0.0f, 0.0f, 0.0f, 0.0f, 0.0f, 0.0f };

int64_t N = 6;

stdlib_strided_smskmap( N, X, 1, M, 1, Y, 1, scale );
```

The function accepts the following arguments:

-   **N**: `[in] int64_t` number of indexed elements.
-   **X**: `[in] float*` input array.
-   **strideX** `[in] int64_t` index increment for `X`.
-   **Mask**: `[in] uint8_t*` mask array.
-   **strideMask**: `[in] int64_t` index increment for `Mask`.
-   **Y**: `[out] float*` output array.
-   **strideY**: `[in] int64_t` index increment for `Y`.
-   **fcn**: `[in] float (*fcn)( float )` unary function to apply.

```c
void stdlib_strided_smskmap( const int64_t N, const float *X, const int64_t strideX, const uint8_t *Mask, const int64_t strideMask, float *Y, const int64_t strideY, float (*fcn)( float ) );
```

</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/strided/base/smskmap.h"
#include <stdint.h>
#include <stdio.h>
#include <inttypes.h>

// Define a callback:
static float scale( const float x ) {
    return x * 10.0f;
}

int main() {
    // Create an input strided array:
    float X[] = { 1.0f, 2.0f, 3.0f, 4.0f, 5.0f, 6.0f };

    // Create a mask strided array:
    uint8_t M[] = { 0, 0, 1, 0, 0, 1 };

    // Create an output strided array:
    float Y[] = { 0.0f, 0.0f, 0.0f, 0.0f, 0.0f, 0.0f };

    // Specify the number of elements:
    int64_t N = 6;

    // Define the strides:
    int64_t strideX = 1;
    int64_t strideM = 1;
    int64_t strideY = -1;

    // Apply the callback:
    stdlib_strided_smskmap( N, X, strideX, M, strideM, Y, strideY, scale );

    // Print the results:
    for ( int64_t i = 0; i < N; i++ ) {
        printf( "Y[ %"PRId64" ] = %f\n", i, Y[ i ] );
    }
}
```

</section>

<!-- /.examples -->

</section>

<!-- /.c -->

<section class="links">

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

[@stdlib/array/uint8]: https://www.npmjs.com/package/@stdlib/array-uint8

</section>

<!-- /.links -->