gdal-async
Version:
Bindings to GDAL (Geospatial Data Abstraction Library) with full async support
99 lines • 2.73 kB
JavaScript
;
// Tar can encode large and negative numbers using a leading byte of
// 0xff for negative, and 0x80 for positive.
Object.defineProperty(exports, "__esModule", { value: true });
exports.parse = exports.encode = void 0;
const encode = (num, buf) => {
if (!Number.isSafeInteger(num)) {
// The number is so large that javascript cannot represent it with integer
// precision.
throw Error('cannot encode number outside of javascript safe integer range');
}
else if (num < 0) {
encodeNegative(num, buf);
}
else {
encodePositive(num, buf);
}
return buf;
};
exports.encode = encode;
const encodePositive = (num, buf) => {
buf[0] = 0x80;
for (var i = buf.length; i > 1; i--) {
buf[i - 1] = num & 0xff;
num = Math.floor(num / 0x100);
}
};
const encodeNegative = (num, buf) => {
buf[0] = 0xff;
var flipped = false;
num = num * -1;
for (var i = buf.length; i > 1; i--) {
var byte = num & 0xff;
num = Math.floor(num / 0x100);
if (flipped) {
buf[i - 1] = onesComp(byte);
}
else if (byte === 0) {
buf[i - 1] = 0;
}
else {
flipped = true;
buf[i - 1] = twosComp(byte);
}
}
};
const parse = (buf) => {
const pre = buf[0];
const value = pre === 0x80 ? pos(buf.subarray(1, buf.length))
: pre === 0xff ? twos(buf)
: null;
if (value === null) {
throw Error('invalid base256 encoding');
}
if (!Number.isSafeInteger(value)) {
// The number is so large that javascript cannot represent it with integer
// precision.
throw Error('parsed number outside of javascript safe integer range');
}
return value;
};
exports.parse = parse;
const twos = (buf) => {
var len = buf.length;
var sum = 0;
var flipped = false;
for (var i = len - 1; i > -1; i--) {
var byte = Number(buf[i]);
var f;
if (flipped) {
f = onesComp(byte);
}
else if (byte === 0) {
f = byte;
}
else {
flipped = true;
f = twosComp(byte);
}
if (f !== 0) {
sum -= f * Math.pow(256, len - i - 1);
}
}
return sum;
};
const pos = (buf) => {
var len = buf.length;
var sum = 0;
for (var i = len - 1; i > -1; i--) {
var byte = Number(buf[i]);
if (byte !== 0) {
sum += byte * Math.pow(256, len - i - 1);
}
}
return sum;
};
const onesComp = (byte) => (0xff ^ byte) & 0xff;
const twosComp = (byte) => ((0xff ^ byte) + 1) & 0xff;
//# sourceMappingURL=large-numbers.js.map