90 lines
2.1 KiB
JavaScript
90 lines
2.1 KiB
JavaScript
// Source: https://github.com/feross/ieee754/blob/8a0041f3d5e41b7cfcf0e0158fcf84b071709bda/index.js
|
|
/*! ieee754. BSD-3-Clause License. Feross Aboukhadijeh <https://feross.org/opensource> */
|
|
export function read(buffer, offset, isLE, mLen, nBytes) {
|
|
let e, m;
|
|
const eLen = nBytes * 8 - mLen - 1;
|
|
const eMax = (1 << eLen) - 1;
|
|
const eBias = eMax >> 1;
|
|
let nBits = -7;
|
|
let i = isLE ? nBytes - 1 : 0;
|
|
const d = isLE ? -1 : 1;
|
|
let s = buffer[offset + i];
|
|
i += d;
|
|
e = s & (1 << -nBits) - 1;
|
|
s >>= -nBits;
|
|
nBits += eLen;
|
|
while (nBits > 0) {
|
|
e = e * 256 + buffer[offset + i];
|
|
i += d;
|
|
nBits -= 8;
|
|
}
|
|
m = e & (1 << -nBits) - 1;
|
|
e >>= -nBits;
|
|
nBits += mLen;
|
|
while (nBits > 0) {
|
|
m = m * 256 + buffer[offset + i];
|
|
i += d;
|
|
nBits -= 8;
|
|
}
|
|
if (e === 0) {
|
|
e = 1 - eBias;
|
|
} else if (e === eMax) {
|
|
return m ? Number.NaN : (s ? -1 : 1) * Number.POSITIVE_INFINITY;
|
|
} else {
|
|
m = m + Math.pow(2, mLen);
|
|
e = e - eBias;
|
|
}
|
|
return (s ? -1 : 1) * m * Math.pow(2, e - mLen);
|
|
}
|
|
export function write(buffer, value, offset, isLE, mLen, nBytes) {
|
|
let e, m, c;
|
|
let eLen = nBytes * 8 - mLen - 1;
|
|
const eMax = (1 << eLen) - 1;
|
|
const eBias = eMax >> 1;
|
|
const rt = mLen === 23 ? Math.pow(2, -24) - Math.pow(2, -77) : 0;
|
|
let i = isLE ? 0 : nBytes - 1;
|
|
const d = isLE ? 1 : -1;
|
|
const s = value < 0 || value === 0 && 1 / value < 0 ? 1 : 0;
|
|
value = Math.abs(value);
|
|
if (Number.isNaN(value) || value === Number.POSITIVE_INFINITY) {
|
|
m = Number.isNaN(value) ? 1 : 0;
|
|
e = eMax;
|
|
} else {
|
|
e = Math.floor(Math.log2(value));
|
|
if (value * (c = Math.pow(2, -e)) < 1) {
|
|
e--;
|
|
c *= 2;
|
|
}
|
|
value += e + eBias >= 1 ? rt / c : rt * Math.pow(2, 1 - eBias);
|
|
if (value * c >= 2) {
|
|
e++;
|
|
c /= 2;
|
|
}
|
|
if (e + eBias >= eMax) {
|
|
m = 0;
|
|
e = eMax;
|
|
} else if (e + eBias >= 1) {
|
|
m = (value * c - 1) * Math.pow(2, mLen);
|
|
e = e + eBias;
|
|
} else {
|
|
m = value * Math.pow(2, eBias - 1) * Math.pow(2, mLen);
|
|
e = 0;
|
|
}
|
|
}
|
|
while (mLen >= 8) {
|
|
buffer[offset + i] = m & 255;
|
|
i += d;
|
|
m /= 256;
|
|
mLen -= 8;
|
|
}
|
|
e = e << mLen | m;
|
|
eLen += mLen;
|
|
while (eLen > 0) {
|
|
buffer[offset + i] = e & 255;
|
|
i += d;
|
|
e /= 256;
|
|
eLen -= 8;
|
|
}
|
|
buffer[offset + i - d] |= s * 128;
|
|
}
|