115 lines
3.1 KiB
JavaScript
115 lines
3.1 KiB
JavaScript
'use strict';
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// IEEE754 conversions based on https://github.com/feross/ieee754
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var sign = require('../internals/math-sign');
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var trunc = require('../internals/math-trunc');
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var $Array = Array;
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var abs = Math.abs;
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var pow = Math.pow;
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var floor = Math.floor;
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var log = Math.log;
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var LN2 = Math.LN2;
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var roundToEven = function (number) {
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var truncated = trunc(number);
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var delta = abs(number - truncated);
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if (delta > 0.5 || delta === 0.5 && truncated % 2 !== 0) {
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return truncated + sign(number);
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} return truncated;
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};
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var pack = function (number, mantissaLength, bytes) {
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var buffer = $Array(bytes);
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var exponentLength = bytes * 8 - mantissaLength - 1;
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var eMax = (1 << exponentLength) - 1;
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var eBias = eMax >> 1;
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var rt = mantissaLength === 23 ? pow(2, -24) - pow(2, -77) : 0;
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var s = number < 0 || number === 0 && 1 / number < 0 ? 1 : 0;
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var index = 0;
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var exponent, mantissa, c;
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number = abs(number);
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// eslint-disable-next-line no-self-compare -- NaN check
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if (number !== number || number === Infinity) {
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// eslint-disable-next-line no-self-compare -- NaN check
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mantissa = number !== number ? 1 : 0;
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exponent = eMax;
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} else {
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exponent = floor(log(number) / LN2);
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c = pow(2, -exponent);
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if (number * c < 1) {
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exponent--;
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c *= 2;
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}
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if (exponent + eBias >= 1) {
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number += rt / c;
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} else {
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number += rt * pow(2, 1 - eBias);
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}
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if (number * c >= 2) {
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exponent++;
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c /= 2;
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}
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if (exponent + eBias >= eMax) {
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mantissa = 0;
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exponent = eMax;
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} else if (exponent + eBias >= 1) {
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mantissa = roundToEven((number * c - 1) * pow(2, mantissaLength));
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exponent += eBias;
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} else {
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mantissa = roundToEven(number * pow(2, eBias - 1) * pow(2, mantissaLength));
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exponent = 0;
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}
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}
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while (mantissaLength >= 8) {
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buffer[index++] = mantissa & 255;
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mantissa /= 256;
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mantissaLength -= 8;
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}
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exponent = exponent << mantissaLength | mantissa;
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exponentLength += mantissaLength;
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while (exponentLength > 0) {
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buffer[index++] = exponent & 255;
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exponent /= 256;
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exponentLength -= 8;
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}
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buffer[--index] |= s * 128;
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return buffer;
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};
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var unpack = function (buffer, mantissaLength) {
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var bytes = buffer.length;
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var exponentLength = bytes * 8 - mantissaLength - 1;
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var eMax = (1 << exponentLength) - 1;
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var eBias = eMax >> 1;
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var nBits = exponentLength - 7;
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var index = bytes - 1;
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var s = buffer[index--];
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var exponent = s & 127;
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var mantissa;
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s >>= 7;
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while (nBits > 0) {
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exponent = exponent * 256 + buffer[index--];
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nBits -= 8;
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}
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mantissa = exponent & (1 << -nBits) - 1;
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exponent >>= -nBits;
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nBits += mantissaLength;
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while (nBits > 0) {
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mantissa = mantissa * 256 + buffer[index--];
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nBits -= 8;
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}
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if (exponent === 0) {
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exponent = 1 - eBias;
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} else if (exponent === eMax) {
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return mantissa ? NaN : s ? -Infinity : Infinity;
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} else {
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mantissa += pow(2, mantissaLength);
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exponent -= eBias;
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} return (s ? -1 : 1) * mantissa * pow(2, exponent - mantissaLength);
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};
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module.exports = {
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pack: pack,
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unpack: unpack
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};
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