D7net
Home
Console
Upload
information
Create File
Create Folder
About
Tools
:
/
proc
/
self
/
root
/
lib
/
node_modules
/
npm
/
node_modules
/
tar
/
lib
/
Filename :
large-numbers.js
back
Copy
'use strict' // Tar can encode large and negative numbers using a leading byte of // 0xff for negative, and 0x80 for positive. const encode = exports.encode = (num, buf) => { if (!Number.isSafeInteger(num)) // The number is so large that javascript cannot represent it with integer // precision. throw TypeError('cannot encode number outside of javascript safe integer range') else if (num < 0) encodeNegative(num, buf) else encodePositive(num, buf) return buf } 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 = exports.parse = (buf) => { var post = buf[buf.length - 1] var pre = buf[0] var value; if (pre === 0x80) value = pos(buf.slice(1, buf.length)) else if (pre === 0xff) value = twos(buf) else throw TypeError('invalid base256 encoding') if (!Number.isSafeInteger(value)) // The number is so large that javascript cannot represent it with integer // precision. throw TypeError('parsed number outside of javascript safe integer range') return value } const twos = (buf) => { var len = buf.length var sum = 0 var flipped = false for (var i = len - 1; i > -1; i--) { var byte = 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 = 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