time-to-botec

README.md (4360B)

---

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 # frexp
 
 > Split a [double-precision floating-point number][ieee754] into a normalized fraction and an integer power of two.
 
 <section class="usage">
 
 ## Usage
 
 ```javascript
 var frexp = require( '@stdlib/math/base/special/frexp' );
 ```
 
 #### frexp( \[out,] x )
 
 Splits a [double-precision floating-point number][ieee754] into a normalized fraction and an integer power of two.
 
 ```javascript
 var out = frexp( 4.0 );
 // returns [ 0.5, 3 ]
 ```
 
 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`.
 
 ```javascript
 var pow = require( '@stdlib/math/base/special/pow' );
 
 var x = 4.0;
 var out = frexp( x );
 // returns [ 0.5, 3 ]
 
 var frac = out[ 0 ];
 var exp = out[ 1 ];
 
 var bool = ( x === frac * pow(2.0, exp) );
 // returns true
 ```
 
 To avoid unnecessary memory allocation, the function supports providing an output (destination) object.
 
 ```javascript
 var Float64Array = require( '@stdlib/array/float64' );
 
 var out = new Float64Array( 2 );
 
 var y = frexp( out, 4.0 );
 // returns <Float64Array>[ 0.5, 3 ]
 
 var bool = ( y === out );
 // returns true
 ```
 
 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`.
 
 ```javascript
 var out = frexp( 0.0 );
 // returns [ 0.0, 0 ]
 
 out = frexp( -0.0 );
 // returns [ -0.0, 0 ]
 
 out = frexp( NaN );
 // returns [ NaN, 0 ]
 
 out = frexp( Infinity );
 // returns [ Infinity, 0 ]
 
 out = frexp( -Infinity );
 // returns [ -Infinity, 0 ]
 ```
 
 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)`.
 
 </section>
 
 <!-- /.usage -->
 
 <section class="notes">
 
 ## Notes
 
 -   Care should be taken when reconstituting a [double-precision floating-point number][ieee754] from a normalized fraction and an exponent. For example,
 
     ```javascript
     var pow = require( '@stdlib/math/base/special/pow' );
 
     var x = 8.988939926493918e+307; // x ~ 2^1023
 
     var out = frexp( x );
     // returns [ 0.5000263811533315, 1024 ]
 
     // Naive reconstitution:
     var y = out[ 0 ] * pow( 2.0, out[ 1 ] );
     // returns Infinity
 
     // Account for 2^1024 evaluating as infinity by recognizing 2^1024 = 2^1 * 2^1023:
     y = out[ 0 ] * pow( 2.0, out[1]-1023 ) * pow( 2.0, 1023 );
     // returns 8.988939926493918e+307
     ```
 
 </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 pow = require( '@stdlib/math/base/special/pow' );
 var BIAS = require( '@stdlib/constants/float64/exponent-bias' );
 var frexp = require( '@stdlib/math/base/special/frexp' );
 
 var sign;
 var frac;
 var exp;
 var x;
 var f;
 var v;
 var i;
 
 // Generate random numbers and break each into a normalized fraction and an integer power of two...
 for ( i = 0; i < 100; i++ ) {
     if ( randu() < 0.5 ) {
         sign = -1.0;
     } else {
         sign = 1.0;
     }
     frac = randu() * 10.0;
     exp = round( randu()*616.0 ) - 308;
     x = sign * frac * pow( 10.0, exp );
     f = frexp( x );
     if ( f[ 1 ] > BIAS ) {
         v = f[ 0 ] * pow( 2.0, f[1]-BIAS ) * pow( 2.0, BIAS );
     } else {
         v = f[ 0 ] * pow( 2.0, f[ 1 ] );
     }
     console.log( '%d = %d * 2^%d = %d', x, f[ 0 ], f[ 1 ], v );
 }
 ```
 
 </section>
 
 <!-- /.examples -->
 
 <section class="links">
 
 [ieee754]: https://en.wikipedia.org/wiki/IEEE_754-1985
 
 [@stdlib/math/base/special/abs]: https://www.npmjs.com/package/@stdlib/math/tree/main/base/special/abs
 
 </section>
 
 <!-- /.links -->