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# Signum

> [Signum][signum] function.

<section class="intro">

The [signum][signum] function is defined as

<!-- <equation class="equation" label="eq:signum_function" align="center" raw="\operatorname{sign}(x) := \begin{cases} -1 & \textrm{if}\ x < 0 \\ 0 & \textrm{if}\ x = 0 \\ 1 & \textrm{if}\ x > 0 \end{cases}" alt="Signum function"> -->

<div class="equation" align="center" data-raw-text="\operatorname{sign}(x) := \begin{cases} -1 &amp; \textrm{if}\ x &lt; 0 \\ 0 &amp; \textrm{if}\ x = 0 \\ 1 &amp; \textrm{if}\ x &gt; 0 \end{cases}" data-equation="eq:signum_function">
    <img src="https://cdn.jsdelivr.net/gh/stdlib-js/stdlib@4e38532a2ca3d2a641daa792a9c4c0fce3e749eb/lib/node_modules/@stdlib/math/base/special/signumf/docs/img/equation_signum_function.svg" alt="Signum function">
    <br>
</div>

<!-- </equation> -->

for any real number `x`.

</section>

<!-- /.intro -->

<section class="usage">

## Usage

```javascript
var signumf = require( '@stdlib/math/base/special/signumf' );
```

#### signumf( x )

Evaluates the [signum][signum] function for a single-precision floating-point number.

```javascript
var sign = signumf( -5.0 );
// returns -1

sign = signumf( 5.0 );
// returns 1

sign = signumf( -0.0 );
// returns -0

sign = signumf( 0.0 );
// returns 0

sign = signumf( NaN );
// returns NaN
```

</section>

<!-- /.usage -->

<section class="notes">

## Notes

Table of results:

| Value   | Sign  |
| ------- | ----- |
| `x > 0` | `+1`  |
| `x < 0` | `-1`  |
| `0`     | `0`   |
| `-0`    | `-0`  |
| `NaN`   | `NaN` |

</section>

<!-- /.notes -->

<section class="examples">

## Examples

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

```javascript
var randu = require( '@stdlib/random/base/randu' );
var round = require( '@stdlib/math/base/special/round' );
var signumf = require( '@stdlib/math/base/special/signumf' );

var sign;
var x;
var i;

for ( i = 0; i < 100; i++ ) {
    x = round( randu()*100.0 ) - 50.0;
    sign = signumf( x );
    console.log( 'signum(%d) = %d', x, sign );
}
```

</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/math/base/special/signumf.h"
```

#### stdlib_base_signumf( x )

Evaluates the [signum][signum] function for a single-precision floating-point number.

```c
float y = stdlib_base_signumf( -9.0f );
// returns -1.0f
```

The function accepts the following arguments:

-   **x**: `[in] float` input value.

```c
float stdlib_base_signumf( const float x );
```

</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/math/base/special/signumf.h"
#include <stdio.h>

int main() {
    float x[] = { 3.14f, -3.14f, 0.0f, 0.0f/0.0f };

    float y;
    int i;
    for ( i = 0; i < 4; i++ ) {
        y = stdlib_base_signumf( x[ i ] );
        printf( "signum(%f) = %f\n", x[ i ], y );
    }
}
```

</section>

<!-- /.examples -->

</section>

<!-- /.c -->

<section class="links">

[signum]: http://en.wikipedia.org/wiki/Sign_function

</section>

<!-- /.links -->