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