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