89 lines
1.9 KiB
JavaScript
89 lines
1.9 KiB
JavaScript
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/* eslint no-bitwise: "off" */
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// Credit: https://github.com/paulmillr/es6-shim/
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"use strict";
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var abs = Math.abs
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, floor = Math.floor
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, log = Math.log
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, min = Math.min
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, pow = Math.pow
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, LN2 = Math.LN2
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, roundToEven;
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roundToEven = function (num) {
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var whole = floor(num), fraction = num - whole;
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if (fraction < 0.5) return whole;
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if (fraction > 0.5) return whole + 1;
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return whole % 2 ? whole + 1 : whole;
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};
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// eslint-disable-next-line max-statements
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module.exports = function (value, ebits, fbits) {
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var bias = (1 << (ebits - 1)) - 1, sign, e, fraction, i, bits, str, bytes;
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// Compute sign, exponent, fraction
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if (isNaN(value)) {
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// NaN
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// http://dev.w3.org/2006/webapi/WebIDL/#es-type-mapping
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e = (1 << ebits) - 1;
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fraction = pow(2, fbits - 1);
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sign = 0;
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} else if (value === Infinity || value === -Infinity) {
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e = (1 << ebits) - 1;
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fraction = 0;
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sign = value < 0 ? 1 : 0;
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} else if (value === 0) {
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e = 0;
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fraction = 0;
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sign = 1 / value === -Infinity ? 1 : 0;
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} else {
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sign = value < 0;
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value = abs(value);
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if (value >= pow(2, 1 - bias)) {
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e = min(floor(log(value) / LN2), 1023);
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fraction = roundToEven(value / pow(2, e) * pow(2, fbits));
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if (fraction / pow(2, fbits) >= 2) {
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e += 1;
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fraction = 1;
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}
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if (e > bias) {
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// Overflow
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e = (1 << ebits) - 1;
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fraction = 0;
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} else {
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// Normal
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e += bias;
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fraction -= pow(2, fbits);
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}
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} else {
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// Subnormal
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e = 0;
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fraction = roundToEven(value / pow(2, 1 - bias - fbits));
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}
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}
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// Pack sign, exponent, fraction
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bits = [];
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for (i = fbits; i; i -= 1) {
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bits.push(fraction % 2 ? 1 : 0);
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fraction = floor(fraction / 2);
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}
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for (i = ebits; i; i -= 1) {
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bits.push(e % 2 ? 1 : 0);
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e = floor(e / 2);
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}
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bits.push(sign ? 1 : 0);
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bits.reverse();
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str = bits.join("");
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// Bits to bytes
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bytes = [];
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while (str.length) {
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bytes.push(parseInt(str.substring(0, 8), 2));
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str = str.substring(8);
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}
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return bytes;
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};
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