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/* |
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* Copyright (c) 2017-2018 Rafael da Silva Rocha. |
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* Copyright (c) 2013 DeNA Co., Ltd. |
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* |
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* Permission is hereby granted, free of charge, to any person obtaining |
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* a copy of this software and associated documentation files (the |
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* "Software"), to deal in the Software without restriction, including |
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* without limitation the rights to use, copy, modify, merge, publish, |
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* distribute, sublicense, and/or sell copies of the Software, and to |
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* permit persons to whom the Software is furnished to do so, subject to |
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* the following conditions: |
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* |
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* The above copyright notice and this permission notice shall be |
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* included in all copies or substantial portions of the Software. |
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* |
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* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, |
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* EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF |
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* MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND |
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* NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE |
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* LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION |
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* OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION |
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* WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE. |
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* |
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*/ |
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/** |
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* @fileoverview Functions to work with IEEE 754 floating point numbers. |
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* @see https://github.com/rochars/byte-data |
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* @see https://github.com/kazuho/ieee754.js |
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*/ |
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/** |
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* Unpack a IEEE754 floating point number. |
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* |
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* Derived from IEEE754 by DeNA Co., Ltd., MIT License. |
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* Adapted to handle NaN. Should port the solution to the original repo. |
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* @see https://github.com/kazuho/ieee754.js/blob/master/ieee754.js |
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* @param {!Uint8Array|!Array<number>} bytes The byte buffer to unpack. |
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* @param {number} offset the start index to read. |
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* @param {number} numBytes the number of bytes used by the number. |
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* @param {number} exponentBits The number of bits of the exponent. |
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* @param {number} exponentBias The exponent bias. |
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*/ |
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export function unpackIEEE754(bytes, offset, numBytes, exponentBits, exponentBias) { |
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let eMax = (1 << exponentBits) - 1; |
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let bias = Math.pow(2, -(8 * numBytes - 1 - exponentBits)); |
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let significand; |
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let leftBits = ""; |
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for (let i = numBytes - 1; i >= 0 ; i--) { |
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let t = bytes[i + offset].toString(2); |
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leftBits += "00000000".substring(t.length) + t; |
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} |
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let sign = leftBits.charAt(0) == "1" ? -1 : 1; |
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leftBits = leftBits.substring(1); |
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let exponent = parseInt(leftBits.substring(0, exponentBits), 2); |
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leftBits = leftBits.substring(exponentBits); |
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if (exponent == eMax) { |
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if (parseInt(leftBits, 2) !== 0) { |
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return NaN; |
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} else { |
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return sign * Infinity; |
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} |
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} else if (exponent == 0) { |
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exponent += 1; |
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significand = parseInt(leftBits, 2); |
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} else { |
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significand = parseInt("1" + leftBits, 2); |
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} |
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return sign * significand * bias * Math.pow(2, exponent - exponentBias); |
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} |
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