_pack-ieee754.js
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/* 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;
};