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‎lib/node_modules/@stdlib/math/base/special/frexpf/README.md‎

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<!--
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@license Apache-2.0
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Copyright (c) 2018 The Stdlib Authors.
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Licensed under the Apache License, Version 2.0 (the "License");
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you may not use this file except in compliance with the License.
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You may obtain a copy of the License at
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http://www.apache.org/licenses/LICENSE-2.0
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Unless required by applicable law or agreed to in writing, software
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distributed under the License is distributed on an "AS IS" BASIS,
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WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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See the License for the specific language governing permissions and
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limitations under the License.
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-->
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# frexp
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> Split a [double-precision floating-point number][ieee754] into a normalized fraction and an integer power of two.
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<section class="usage">
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## Usage
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```javascript
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var frexp = require( '@stdlib/math/base/special/frexp' );
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```
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#### frexp( x )
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Splits a [double-precision floating-point number][ieee754] into a normalized fraction and an integer power of two.
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```javascript
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var out = frexp( 4.0 );
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// returns [ 0.5, 3 ]
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```
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By default, the function returns the normalized fraction and the exponent as a two-element `array`. The normalized fraction and exponent satisfy the relation `x = frac * 2^exp`.
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```javascript
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var pow = require( '@stdlib/math/base/special/pow' );
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var x = 4.0;
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var out = frexp( x );
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// returns [ 0.5, 3 ]
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var frac = out[ 0 ];
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var exp = out[ 1 ];
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var bool = ( x === frac * pow(2.0, exp) );
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// returns true
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```
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If provided positive or negative zero, `NaN`, or positive or negative `infinity`, the function returns a two-element `array` containing the input value and an exponent equal to `0`.
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```javascript
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var out = frexp( 0.0 );
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// returns [ 0.0, 0 ]
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out = frexp( -0.0 );
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// returns [ -0.0, 0 ]
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out = frexp( NaN );
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// returns [ NaN, 0 ]
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out = frexp( Infinity );
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// returns [ Infinity, 0 ]
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out = frexp( -Infinity );
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// returns [ -Infinity, 0 ]
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```
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For all other numeric input values, the [absolute value][@stdlib/math/base/special/abs] of the normalized fraction resides on the interval `[0.5,1)`.
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#### frexp.assign( x, out, stride, offset )
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Splits a [double-precision floating-point number][ieee754] into a normalized fraction and an integer power of two and assigns results to a provided output array.
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```javascript
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var Float64Array = require( '@stdlib/array/float64' );
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var out = new Float64Array( 2 );
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var y = frexp.assign( 4.0, out, 1, 0 );
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// returns <Float64Array>[ 0.5, 3 ]
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var bool = ( y === out );
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// returns true
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```
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</section>
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<!-- /.usage -->
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<section class="notes">
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## Notes
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- Care should be taken when reconstituting a [double-precision floating-point number][ieee754] from a normalized fraction and an exponent. For example,
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```javascript
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var pow = require( '@stdlib/math/base/special/pow' );
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var x = 8.988939926493918e+307; // x ~ 2^1023
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var out = frexp( x );
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// returns [ 0.5000263811533315, 1024 ]
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// Naive reconstitution:
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var y = out[ 0 ] * pow( 2.0, out[ 1 ] );
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// returns Infinity
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// Account for 2^1024 evaluating as infinity by recognizing 2^1024 = 2^1 * 2^1023:
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y = out[ 0 ] * pow( 2.0, out[1]-1023 ) * pow( 2.0, 1023 );
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// returns 8.988939926493918e+307
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```
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</section>
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<!-- /.notes -->
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<section class="examples">
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## Examples
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<!-- eslint no-undef: "error" -->
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```javascript
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var randu = require( '@stdlib/random/base/randu' );
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var round = require( '@stdlib/math/base/special/round' );
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var pow = require( '@stdlib/math/base/special/pow' );
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var BIAS = require( '@stdlib/constants/float64/exponent-bias' );
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var frexp = require( '@stdlib/math/base/special/frexp' );
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var sign;
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var frac;
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var exp;
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var x;
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var f;
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var v;
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var i;
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// Generate random numbers and break each into a normalized fraction and an integer power of two...
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for ( i = 0; i < 100; i++ ) {
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if ( randu() < 0.5 ) {
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sign = -1.0;
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} else {
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sign = 1.0;
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}
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frac = randu() * 10.0;
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exp = round( randu()*616.0 ) - 308;
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x = sign * frac * pow( 10.0, exp );
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f = frexp( x );
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if ( f[ 1 ] > BIAS ) {
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v = f[ 0 ] * pow( 2.0, f[1]-BIAS ) * pow( 2.0, BIAS );
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} else {
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v = f[ 0 ] * pow( 2.0, f[ 1 ] );
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}
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console.log( '%d = %d * 2^%d = %d', x, f[ 0 ], f[ 1 ], v );
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}
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```
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</section>
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<!-- /.examples -->
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<!-- C interface documentation. -->
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* * *
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<section class="c">
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## C APIs
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<!-- Section to include introductory text. Make sure to keep an empty line after the intro `section` element and another before the `/section` close. -->
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<section class="intro">
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</section>
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<!-- /.intro -->
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<!-- C usage documentation. -->
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<section class="usage">
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### Usage
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```c
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#include "stdlib/math/base/special/frexp.h"
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```
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#### stdlib_base_frexp( x, frac, exp )
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Splits a [double-precision floating-point number][ieee754] into a normalized fraction and an integer power of two.
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```c
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#include <stdint.h>
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double frac;
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int32_t exp;
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stdlib_base_frexp( 4.0, &frac, &exp );
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```
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The function accepts the following arguments:
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- **x**: `[in] double` input value.
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- **frac**: `[out] double*` destination for the normalized fraction.
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- **exp**: `[out] int32_t*` destination for the integer power of two.
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```c
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void stdlib_base_frexp( const double x, double *frac, int32_t *exp );
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```
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</section>
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<!-- /.usage -->
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<!-- C API usage notes. Make sure to keep an empty line after the `section` element and another before the `/section` close. -->
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<section class="notes">
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</section>
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<!-- /.notes -->
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<!-- C API usage examples. -->
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<section class="examples">
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### Examples
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```c
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#include "stdlib/math/base/special/frexp.h"
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#include <stdint.h>
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#include <stdio.h>
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#include <inttypes.h>
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int main( void ) {
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const double x[] = { 4.0, 0.0, -0.0, 1.0, -1.0, 3.14, -3.14, 1.0e308, -1.0e308, 1.0/0.0, -1.0/0.0, 0.0/0.0 };
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double frac;
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int32_t exp;
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int i;
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for ( i = 0; i < 12; i++ ) {
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stdlib_base_frexp( x[i], &frac, &exp );
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printf( "x: %f => frac: %f, exp: %" PRId32 "\n", x[i], frac, exp );
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}
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}
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```
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</section>
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<!-- /.examples -->
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</section>
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<!-- /.c -->
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<!-- Section for related `stdlib` packages. Do not manually edit this section, as it is automatically populated. -->
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<section class="related">
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* * *
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## See Also
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- <span class="package-name">[`@stdlib/math/base/special/ldexp`][@stdlib/math/base/special/ldexp]</span><span class="delimiter">: </span><span class="description">multiply a double-precision floating-point number by an integer power of two.</span>
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</section>
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<!-- /.related -->
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<!-- Section for all links. Make sure to keep an empty line after the `section` element and another before the `/section` close. -->
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<section class="links">
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[ieee754]: https://en.wikipedia.org/wiki/IEEE_754-1985
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[@stdlib/math/base/special/abs]: https://github.com/stdlib-js/stdlib/tree/develop/lib/node_modules/%40stdlib/math/base/special/abs
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<!-- <related-links> -->
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[@stdlib/math/base/special/ldexp]: https://github.com/stdlib-js/stdlib/tree/develop/lib/node_modules/%40stdlib/math/base/special/ldexp
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<!-- </related-links> -->
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</section>
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<!-- /.links -->

‎lib/node_modules/@stdlib/math/base/special/frexpf/benchmark/benchmark.js‎

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/**
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* @license Apache-2.0
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*
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* Copyright (c) 2018 The Stdlib Authors.
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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'use strict';
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// MODULES //
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var bench = require( '@stdlib/bench' );
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var randu = require( '@stdlib/random/base/randu' );
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var isArray = require( '@stdlib/assert/is-array' );
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var pkg = require( './../package.json' ).name;
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var frexp = require( './../lib' );
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// MAIN //
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bench( pkg, function benchmark( b ) {
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var x;
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var y;
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var i;
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b.tic();
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for ( i = 0; i < b.iterations; i++ ) {
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x = ( randu()*1.0e7 ) - 5.0e6;
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y = frexp( x );
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if ( typeof out !== 'object' ) {
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b.fail( 'should return an array' );
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}
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}
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b.toc();
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if ( !isArray( y ) ) {
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b.fail( 'should return an array' );
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}
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b.pass( 'benchmark finished' );
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b.end();
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});
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bench( pkg+':assign', function benchmark( b ) {
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var out;
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var x;
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var y;
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var i;
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out = [ 0.0, 0.0 ];
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b.tic();
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for ( i = 0; i < b.iterations; i++ ) {
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x = ( randu()*1.0e7 ) - 5.0e6;
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y = frexp.assign( x, out, 1, 0 );
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if ( typeof out !== 'object' ) {
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b.fail( 'should return an array' );
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}
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}
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b.toc();
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if ( !isArray( y ) || y !== out ) {
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b.fail( 'should return the output array' );
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}
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b.pass( 'benchmark finished' );
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b.end();
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});

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