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# evalpoly

> Compile a C function for evaluating a [polynomial][@stdlib/math/base/tools/evalpoly].

<section class="intro">

</section>

<!-- /.intro -->

<section class="usage">

## Usage

```javascript
var compile = require( '@stdlib/math/base/tools/evalpoly-compile-c' );
```

#### compile( c\[, options] )

Compiles a C function for evaluating a [polynomial][@stdlib/math/base/tools/evalpoly] having coefficients `c`.

```javascript
var str = compile( [ 3.0, 2.0, 1.0 ] );
// returns <string>
```

The function supports the following `options`:

-   **dtype**: input argument floating-point data type (e.g., `double` or `float`). Default: `'double'`.
-   **name**: function name. Default: `'evalpoly'`.

In the example above, the output string would correspond to the following function:

```c
/**
* Evaluates a polynomial.
*
* ## Notes
*
* -   The implementation uses [Horner's rule][horners-method] for efficient computation.
*
* [horners-method]: https://en.wikipedia.org/wiki/Horner%27s_method
*
* @param x   value at which to evaluate the polynomial
* @return    evaluated polynomial
*/
static double evalpoly( const double x ) {
    return 3.0 + (x * (2.0 + (x * 1.0)));
}
```

To generate a function having a custom name and supporting single-precision floating-point numbers, provide the corresponding options.

```javascript
var opts = {
    'dtype': 'float',
    'name': 'polyval123'
};
var str = compile( [ 3.0, 2.0, 1.0 ], opts );
// returns <string>
```

For the previous example, the output string would correspond to the following function:

```c
/**
* Evaluates a polynomial.
*
* ## Notes
*
* -   The implementation uses [Horner's rule][horners-method] for efficient computation.
*
* [horners-method]: https://en.wikipedia.org/wiki/Horner%27s_method
*
* @param x   value at which to evaluate the polynomial
* @return    evaluated polynomial
*/
static float polyval123( const float x ) {
    return 3.0f + (x * (2.0f + (x * 1.0f)));
}
```

</section>

<!-- /.usage -->

<section class="notes">

## Notes

-   The coefficients should be ordered in **ascending** degree, thus matching summation notation.
-   The function is intended for **non-browser** environments for the purpose of generating functions for inclusion in source files.

</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 Float64Array = require( '@stdlib/array/float64' );
var compile = require( '@stdlib/math/base/tools/evalpoly-compile-c' );

var coef;
var sign;
var str;
var i;

// Create an array of random coefficients...
coef = new Float64Array( 10 );
for ( i = 0; i < coef.length; i++ ) {
    if ( randu() < 0.5 ) {
        sign = -1.0;
    } else {
        sign = 1.0;
    }
    coef[ i ] = sign * round( randu()*100.0 );
}

// Compile a function for evaluating a polynomial:
str = compile( coef );
console.log( str );
```

</section>

<!-- /.examples -->

<!-- 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/math/base/tools/evalpoly]: https://github.com/stdlib-js/math/tree/main/base/tools/evalpoly

</section>

<!-- /.links -->
