87 lines
2.7 KiB
JavaScript
87 lines
2.7 KiB
JavaScript
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// IEEE754 conversions based on https://github.com/feross/ieee754
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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 pack = function (number, mantissaLength, bytes) {
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var buffer = new 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 sign = 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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if (number * (c = pow(2, -exponent)) < 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 = (number * c - 1) * pow(2, mantissaLength);
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exponent = exponent + eBias;
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} else {
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mantissa = 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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for (; mantissaLength >= 8; buffer[index++] = mantissa & 255, mantissa /= 256, mantissaLength -= 8);
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exponent = exponent << mantissaLength | mantissa;
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exponentLength += mantissaLength;
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for (; exponentLength > 0; buffer[index++] = exponent & 255, exponent /= 256, exponentLength -= 8);
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buffer[--index] |= sign * 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 sign = buffer[index--];
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var exponent = sign & 127;
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var mantissa;
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sign >>= 7;
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for (; nBits > 0; exponent = exponent * 256 + buffer[index], index--, nBits -= 8);
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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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for (; nBits > 0; mantissa = mantissa * 256 + buffer[index], index--, nBits -= 8);
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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 : sign ? -Infinity : Infinity;
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} else {
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mantissa = mantissa + pow(2, mantissaLength);
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exponent = exponent - eBias;
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} return (sign ? -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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