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* @license Apache-2.0
*
* Copyright (c) 2018 The Stdlib Authors.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
'use strict';
// MODULES //
var isnan = require( '@stdlib/math/base/assert/is-nan' );
var isInfinite = require( '@stdlib/math/base/assert/is-infinite' );
var normalize = require( '@stdlib/number/float64/base/normalize' ).assign;
var floatExp = require( '@stdlib/number/float64/base/exponent' );
var toWords = require( '@stdlib/number/float64/base/to-words' );
var fromWords = require( '@stdlib/number/float64/base/from-words' );
// VARIABLES //
// Exponent all 0s: 1 00000000000 11111111111111111111 => 2148532223
var CLEAR_EXP_MASK = 0x800fffff>>>0; // asm type annotation
// Exponent equal to 1022 (BIAS-1): 0 01111111110 00000000000000000000 => 1071644672
var SET_EXP_MASK = 0x3fe00000|0; // asm type annotation
// Normalization workspace:
var X = [ 0.0, 0.0 ]; // WARNING: not thread safe
// High/low words workspace:
var WORDS = [ 0, 0 ]; // WARNING: not thread safe
// MAIN //
/**
* Splits a double-precision floating-point number into a normalized fraction and an integer power of two and assigns results to a provided output array.
*
* @private
* @param {number} x - input value
* @param {Collection} out - output array
* @param {integer} stride - output array stride
* @param {NonNegativeInteger} offset - output array index offset
* @returns {Collection} output array
*
* @example
* var out = frexp( 4.0, new Array( 2 ), 1, 0 );
* // returns [ 0.5, 3 ]
*
* @example
* var out = frexp( 0.0, new Array( 2 ), 1, 0 );
* // returns [ 0.0, 0 ]
*
* @example
* var out = frexp( -0.0, new Array( 2 ), 1, 0 );
* // returns [ -0.0, 0 ]
*
* @example
* var out = frexp( NaN, new Array( 2 ), 1, 0 );
* // returns [ NaN, 0 ]
*
* @example
* var out = frexp( Infinity, new Array( 2 ), 1, 0 );
* // returns [ Infinity , 0 ]
*
* @example
* var out = frexp( -Infinity, new Array( 2 ), 1, 0 );
* // returns [ -Infinity , 0 ]
*/
function frexp( x, out, stride, offset ) {
var high;
var exp;
if (
x === 0.0 || // handles -0
isnan( x ) ||
isInfinite( x )
) {
out[ offset ] = x;
out[ offset + stride ] = 0;
return out;
}
// If `x` is subnormal, normalize it...
normalize( x, X, 1, 0 );
// Extract the exponent from `x` and add the normalization exponent:
exp = floatExp( X[0] ) + X[ 1 ] + 1;
// Break `x` into two unsigned 32-bit integers (higher and lower order words):
toWords.assign( X[ 0 ], WORDS, 1, 0 );
high = WORDS[ 0 ];
// Clear the exponent bits within the higher order word:
high &= CLEAR_EXP_MASK;
// Set the exponent bits within the higher order word to BIAS-1 (1023-1=1022):
high |= SET_EXP_MASK;
// Create a new floating-point number:
x = fromWords( high, WORDS[ 1 ] );
out[ offset ] = x;
out[ offset + stride ] = exp;
return out;
}
// EXPORTS //
module.exports = frexp;
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