time-to-botec

Benchmark sampling in different programming languages
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round2.js (2560B)

      1 /**
      2 * @license Apache-2.0
      3 *
      4 * Copyright (c) 2018 The Stdlib Authors.
      5 *
      6 * Licensed under the Apache License, Version 2.0 (the "License");
      7 * you may not use this file except in compliance with the License.
      8 * You may obtain a copy of the License at
      9 *
     10 *    http://www.apache.org/licenses/LICENSE-2.0
     11 *
     12 * Unless required by applicable law or agreed to in writing, software
     13 * distributed under the License is distributed on an "AS IS" BASIS,
     14 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
     15 * See the License for the specific language governing permissions and
     16 * limitations under the License.
     17 */
     18 
     19 'use strict';
     20 
     21 // MODULES //
     22 
     23 var isnan = require( './../../../../base/assert/is-nan' );
     24 var isInfinite = require( './../../../../base/assert/is-infinite' );
     25 var pow = require( './../../../../base/special/pow' );
     26 var floor = require( './../../../../base/special/floor' );
     27 var ceil = require( './../../../../base/special/ceil' );
     28 var log2 = require( './../../../../base/special/log2' );
     29 var MAX_EXP = require( '@stdlib/constants/float64/max-base2-exponent' );
     30 var MIN_EXP_SUBNORMAL = require( '@stdlib/constants/float64/min-base2-exponent-subnormal' );
     31 var PINF = require( '@stdlib/constants/float64/pinf' );
     32 
     33 
     34 // VARIABLES //
     35 
     36 // 2^1023:
     37 var HUGE = pow( 2.0, MAX_EXP );
     38 var HALF_HUGE = HUGE / 2.0;
     39 
     40 
     41 // MAIN //
     42 
     43 /**
     44 * Rounds a numeric value to the nearest power of two on a linear scale.
     45 *
     46 * @param {number} x - input value
     47 * @returns {number} rounded value
     48 *
     49 * @example
     50 * var v = round2( 3.141592653589793 );
     51 * // returns 4.0
     52 *
     53 * @example
     54 * var v = round2( 13.0 );
     55 * // returns 16.0
     56 *
     57 * @example
     58 * var v = round2( -0.314 );
     59 * // returns -0.25
     60 */
     61 function round2( x ) {
     62 	var sign;
     63 	var half;
     64 	var p1;
     65 	var p2;
     66 	var y1;
     67 	var y2;
     68 	var p;
     69 	if (
     70 		isnan( x ) ||
     71 		isInfinite( x ) ||
     72 		x === 0.0
     73 	) {
     74 		return x;
     75 	}
     76 	if ( x < 0 ) {
     77 		x = -x;
     78 		sign = -1.0;
     79 	} else {
     80 		sign = 1.0;
     81 	}
     82 	// Solve the equation `2^p = x` for `p`:
     83 	p = log2( x );
     84 
     85 	// If provided the smallest subnormal, no rounding possible:
     86 	if ( p === MIN_EXP_SUBNORMAL ) {
     87 		return x;
     88 	}
     89 	// Find the previous and next integer powers:
     90 	p1 = floor( p );
     91 	p2 = ceil( p );
     92 
     93 	// Handle overflow:
     94 	if ( p1 === MAX_EXP ) {
     95 		if ( x - HUGE >= HALF_HUGE ) {
     96 			return sign * PINF; // sign-preserving
     97 		}
     98 		return sign * HUGE;
     99 	}
    100 	// Compute previous and next powers of two:
    101 	y1 = pow( 2.0, p1 );
    102 	y2 = pow( 2.0, p2 );
    103 
    104 	// Find the closest power of two:
    105 	half = ( y2 - y1 ) / 2.0;
    106 	if ( y1+half > x ) {
    107 		return sign * y1;
    108 	}
    109 	return sign * y2;
    110 }
    111 
    112 
    113 // EXPORTS //
    114 
    115 module.exports = round2;