84 lines
2.9 KiB
JavaScript
84 lines
2.9 KiB
JavaScript
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'use strict';
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var GetIntrinsic = require('get-intrinsic');
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var $parseInt = GetIntrinsic('%parseInt%');
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var $abs = GetIntrinsic('%Math.abs%');
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var $floor = GetIntrinsic('%Math.floor%');
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var callBound = require('call-bind/callBound');
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var $strIndexOf = callBound('String.prototype.indexOf');
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var $strSlice = callBound('String.prototype.slice');
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var fractionToBitString = require('../helpers/fractionToBinaryString');
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var intToBinString = require('../helpers/intToBinaryString');
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var isNegativeZero = require('./isNegativeZero');
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var float64bias = 1023;
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var elevenOnes = '11111111111';
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var elevenZeroes = '00000000000';
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var fiftyOneZeroes = elevenZeroes + elevenZeroes + elevenZeroes + elevenZeroes + '0000000';
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// IEEE 754-1985
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module.exports = function valueToFloat64Bytes(value, isLittleEndian) {
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var signBit = value < 0 || isNegativeZero(value) ? '1' : '0';
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var exponentBits;
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var significandBits;
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if (isNaN(value)) {
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exponentBits = elevenOnes;
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significandBits = '1' + fiftyOneZeroes;
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} else if (!isFinite(value)) {
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exponentBits = elevenOnes;
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significandBits = '0' + fiftyOneZeroes;
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} else if (value === 0) {
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exponentBits = elevenZeroes;
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significandBits = '0' + fiftyOneZeroes;
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} else {
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value = $abs(value); // eslint-disable-line no-param-reassign
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// Isolate the integer part (digits before the decimal):
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var integerPart = $floor(value);
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var intBinString = intToBinString(integerPart); // bit string for integer part
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var fracBinString = fractionToBitString(value - integerPart); // bit string for fractional part
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var numberOfBits;
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// find exponent needed to normalize integer+fractional parts
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if (intBinString) {
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exponentBits = intBinString.length - 1; // move the decimal to the left
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} else {
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var first1 = $strIndexOf(fracBinString, '1');
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if (first1 > -1) {
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numberOfBits = first1 + 1;
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}
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exponentBits = -numberOfBits; // move the decimal to the right
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}
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significandBits = intBinString + fracBinString;
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if (exponentBits < 0) {
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// subnormals
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if (exponentBits <= -float64bias) {
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numberOfBits = float64bias - 1; // limit number of removed bits
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}
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significandBits = $strSlice(significandBits, numberOfBits); // remove all leading 0s and the first 1 for normal values; for subnormals, remove up to `float64bias - 1` leading bits
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} else {
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significandBits = $strSlice(significandBits, 1); // remove the leading '1' (implicit/hidden bit)
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}
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exponentBits = $strSlice(elevenZeroes + intToBinString(exponentBits + float64bias), -11); // Convert the exponent to a bit string
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significandBits = $strSlice(significandBits + fiftyOneZeroes + '0', 0, 52); // fill in any trailing zeros and ensure we have only 52 fraction bits
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}
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var bits = signBit + exponentBits + significandBits;
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var rawBytes = [];
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for (var i = 0; i < 8; i++) {
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var targetIndex = isLittleEndian ? 8 - i - 1 : i;
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rawBytes[targetIndex] = $parseInt($strSlice(bits, i * 8, (i + 1) * 8), 2);
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}
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return rawBytes;
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};
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