mirror of
https://github.com/idanoo/GoScrobble.git
synced 2024-11-22 16:35:14 +00:00
87 lines
2.7 KiB
JavaScript
87 lines
2.7 KiB
JavaScript
// IEEE754 conversions based on https://github.com/feross/ieee754
|
|
var abs = Math.abs;
|
|
var pow = Math.pow;
|
|
var floor = Math.floor;
|
|
var log = Math.log;
|
|
var LN2 = Math.LN2;
|
|
|
|
var pack = function (number, mantissaLength, bytes) {
|
|
var buffer = new Array(bytes);
|
|
var exponentLength = bytes * 8 - mantissaLength - 1;
|
|
var eMax = (1 << exponentLength) - 1;
|
|
var eBias = eMax >> 1;
|
|
var rt = mantissaLength === 23 ? pow(2, -24) - pow(2, -77) : 0;
|
|
var sign = number < 0 || number === 0 && 1 / number < 0 ? 1 : 0;
|
|
var index = 0;
|
|
var exponent, mantissa, c;
|
|
number = abs(number);
|
|
// eslint-disable-next-line no-self-compare -- NaN check
|
|
if (number != number || number === Infinity) {
|
|
// eslint-disable-next-line no-self-compare -- NaN check
|
|
mantissa = number != number ? 1 : 0;
|
|
exponent = eMax;
|
|
} else {
|
|
exponent = floor(log(number) / LN2);
|
|
if (number * (c = pow(2, -exponent)) < 1) {
|
|
exponent--;
|
|
c *= 2;
|
|
}
|
|
if (exponent + eBias >= 1) {
|
|
number += rt / c;
|
|
} else {
|
|
number += rt * pow(2, 1 - eBias);
|
|
}
|
|
if (number * c >= 2) {
|
|
exponent++;
|
|
c /= 2;
|
|
}
|
|
if (exponent + eBias >= eMax) {
|
|
mantissa = 0;
|
|
exponent = eMax;
|
|
} else if (exponent + eBias >= 1) {
|
|
mantissa = (number * c - 1) * pow(2, mantissaLength);
|
|
exponent = exponent + eBias;
|
|
} else {
|
|
mantissa = number * pow(2, eBias - 1) * pow(2, mantissaLength);
|
|
exponent = 0;
|
|
}
|
|
}
|
|
for (; mantissaLength >= 8; buffer[index++] = mantissa & 255, mantissa /= 256, mantissaLength -= 8);
|
|
exponent = exponent << mantissaLength | mantissa;
|
|
exponentLength += mantissaLength;
|
|
for (; exponentLength > 0; buffer[index++] = exponent & 255, exponent /= 256, exponentLength -= 8);
|
|
buffer[--index] |= sign * 128;
|
|
return buffer;
|
|
};
|
|
|
|
var unpack = function (buffer, mantissaLength) {
|
|
var bytes = buffer.length;
|
|
var exponentLength = bytes * 8 - mantissaLength - 1;
|
|
var eMax = (1 << exponentLength) - 1;
|
|
var eBias = eMax >> 1;
|
|
var nBits = exponentLength - 7;
|
|
var index = bytes - 1;
|
|
var sign = buffer[index--];
|
|
var exponent = sign & 127;
|
|
var mantissa;
|
|
sign >>= 7;
|
|
for (; nBits > 0; exponent = exponent * 256 + buffer[index], index--, nBits -= 8);
|
|
mantissa = exponent & (1 << -nBits) - 1;
|
|
exponent >>= -nBits;
|
|
nBits += mantissaLength;
|
|
for (; nBits > 0; mantissa = mantissa * 256 + buffer[index], index--, nBits -= 8);
|
|
if (exponent === 0) {
|
|
exponent = 1 - eBias;
|
|
} else if (exponent === eMax) {
|
|
return mantissa ? NaN : sign ? -Infinity : Infinity;
|
|
} else {
|
|
mantissa = mantissa + pow(2, mantissaLength);
|
|
exponent = exponent - eBias;
|
|
} return (sign ? -1 : 1) * mantissa * pow(2, exponent - mantissaLength);
|
|
};
|
|
|
|
module.exports = {
|
|
pack: pack,
|
|
unpack: unpack
|
|
};
|