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;
};