source: imaps-frontend/node_modules/es-abstract/helpers/valueToFloat64Bytes.js

'use strict';

var GetIntrinsic = require('get-intrinsic');

var $parseInt = GetIntrinsic('%parseInt%');
var $abs = GetIntrinsic('%Math.abs%');
var $floor = GetIntrinsic('%Math.floor%');

var callBound = require('call-bind/callBound');

var $strIndexOf = callBound('String.prototype.indexOf');
var $strSlice = callBound('String.prototype.slice');

var fractionToBitString = require('../helpers/fractionToBinaryString');
var intToBinString = require('../helpers/intToBinaryString');
var isNegativeZero = require('./isNegativeZero');

var float64bias = 1023;

var elevenOnes = '11111111111';
var elevenZeroes = '00000000000';
var fiftyOneZeroes = elevenZeroes + elevenZeroes + elevenZeroes + elevenZeroes + '0000000';

// IEEE 754-1985
module.exports = function valueToFloat64Bytes(value, isLittleEndian) {
        var signBit = value < 0 || isNegativeZero(value) ? '1' : '0';
        var exponentBits;
        var significandBits;

        if (isNaN(value)) {
                exponentBits = elevenOnes;
                significandBits = '1' + fiftyOneZeroes;
        } else if (!isFinite(value)) {
                exponentBits = elevenOnes;
                significandBits = '0' + fiftyOneZeroes;
        } else if (value === 0) {
                exponentBits = elevenZeroes;
                significandBits = '0' + fiftyOneZeroes;
        } else {
                value = $abs(value); // eslint-disable-line no-param-reassign

                // Isolate the integer part (digits before the decimal):
                var integerPart = $floor(value);

                var intBinString = intToBinString(integerPart); // bit string for integer part
                var fracBinString = fractionToBitString(value - integerPart); // bit string for fractional part

                var numberOfBits;
                // find exponent needed to normalize integer+fractional parts
                if (intBinString) {
                        exponentBits = intBinString.length - 1; // move the decimal to the left
                } else {
                        var first1 = $strIndexOf(fracBinString, '1');
                        if (first1 > -1) {
                                numberOfBits = first1 + 1;
                        }
                        exponentBits = -numberOfBits; // move the decimal to the right
                }

                significandBits = intBinString + fracBinString;
                if (exponentBits < 0) {
                        // subnormals
                        if (exponentBits <= -float64bias) {
                                numberOfBits = float64bias - 1; // limit number of removed bits
                        }
                        significandBits = $strSlice(significandBits, numberOfBits); // remove all leading 0s and the first 1 for normal values; for subnormals, remove up to `float64bias - 1` leading bits
                } else {
                        significandBits = $strSlice(significandBits, 1); // remove the leading '1' (implicit/hidden bit)
                }
                exponentBits = $strSlice(elevenZeroes + intToBinString(exponentBits + float64bias), -11); // Convert the exponent to a bit string

                significandBits = $strSlice(significandBits + fiftyOneZeroes + '0', 0, 52); // fill in any trailing zeros and ensure we have only 52 fraction bits
        }

        var bits = signBit + exponentBits + significandBits;
        var rawBytes = [];
        for (var i = 0; i < 8; i++) {
                var targetIndex = isLittleEndian ? 8 - i - 1 : i;
                rawBytes[targetIndex] = $parseInt($strSlice(bits, i * 8, (i + 1) * 8), 2);
        }

        return rawBytes;
};