# Signum
> [Signum][signum] function.
The [signum][signum] function is defined as
for any real number `x`.
## Usage
```javascript
var signum = require( '@stdlib/math/base/special/signum' );
```
#### signum( x )
Evaluates the [signum][signum] function for a double-precision floating-point number.
```javascript
var sign = signum( -5.0 );
// returns -1
sign = signum( 5.0 );
// returns 1
sign = signum( -0.0 );
// returns -0
sign = signum( 0.0 );
// returns 0
sign = signum( NaN );
// returns NaN
```
## Notes
Table of results:
| Value | Sign |
| ------- | ----- |
| `x > 0` | `+1` |
| `x < 0` | `-1` |
| `0` | `0` |
| `-0` | `-0` |
| `NaN` | `NaN` |
## Examples
```javascript
var randu = require( '@stdlib/random/base/randu' );
var round = require( '@stdlib/math/base/special/round' );
var signum = require( '@stdlib/math/base/special/signum' );
var sign;
var x;
var i;
for ( i = 0; i < 100; i++ ) {
x = round( randu()*100.0 ) - 50.0;
sign = signum( x );
console.log( 'signum(%d) = %d', x, sign );
}
```
* * *
## C APIs
### Usage
```c
#include "stdlib/math/base/special/signum.h"
```
#### stdlib_base_signum( x )
Evaluates the [signum][signum] function for a double-precision floating-point number.
```c
double y = stdlib_base_signum( -9.0 );
// returns -1.0
```
The function accepts the following arguments:
- **x**: `[in] double` input value.
```c
double stdlib_base_signum( const double x );
```
### Examples
```c
#include "stdlib/math/base/special/signum.h"
#include
int main() {
double x[] = { 3.14, -3.14, 0.0, 0.0/0.0 };
double y;
int i;
for ( i = 0; i < 4; i++ ) {
y = stdlib_base_signum( x[ i ] );
printf( "signum(%lf) = %lf\n", x[ i ], y );
}
}
```
[signum]: http://en.wikipedia.org/wiki/Sign_function
