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Name	Size	Perms	Modified	Actions
[ .. / .. ]
create.js	2.34 KB	-rw-r--r--	2023-01-06 10:00:18	Edit Del
extract.js	2.79 KB	-rw-r--r--	2023-01-06 10:00:18	Edit Del
get-write-flag.js	921 B	-rw-r--r--	2022-10-11 10:59:35	Edit Del
header.js	8.94 KB	-rw-r--r--	2023-01-06 10:00:18	Edit Del
high-level-opt.js	760 B	-rw-r--r--	2022-10-11 10:59:35	Edit Del
large-numbers.js	2.18 KB	-rw-r--r--	2023-01-06 10:00:18	Edit Del
list.js	3.15 KB	-rw-r--r--	2023-01-06 10:00:18	Edit Del
mkdir.js	5.36 KB	-rw-r--r--	2023-01-06 10:00:18	Edit Del
mode-fix.js	649 B	-rw-r--r--	2023-01-06 10:00:18	Edit Del
normalize-unicode.js	412 B	-rw-r--r--	2023-08-09 00:23:21	Edit Del
normalize-windows-path.js	410 B	-rw-r--r--	2022-10-11 10:59:35	Edit Del
pack.js	9.79 KB	-rw-r--r--	2023-10-14 06:00:20	Edit Del
parse.js	15.94 KB	-rw-r--r--	2023-10-14 06:00:20	Edit Del
path-reservations.js	4.31 KB	-rw-r--r--	2023-08-09 00:23:21	Edit Del
pax.js	3.97 KB	-rw-r--r--	2023-01-06 10:00:18	Edit Del
read-entry.js	2.78 KB	-rw-r--r--	2023-06-20 06:00:25	Edit Del
replace.js	5.64 KB	-rw-r--r--	2023-10-14 06:00:20	Edit Del
strip-absolute-path.js	917 B	-rw-r--r--	2023-01-06 10:00:18	Edit Del
strip-trailing-slashes.js	394 B	-rw-r--r--	2022-10-11 10:59:35	Edit Del
types.js	1.07 KB	-rw-r--r--	2022-10-11 10:59:35	Edit Del
unpack.js	25.23 KB	-rw-r--r--	2024-04-25 10:00:17	Edit Del
update.js	937 B	-rw-r--r--	2023-10-14 06:00:20	Edit Del
warn-mixin.js	725 B	-rw-r--r--	2023-01-06 10:00:18	Edit Del
winchars.js	535 B	-rw-r--r--	2022-10-11 10:59:35	Edit Del
write-entry.js	14.94 KB	-rw-r--r--	2023-06-20 06:00:25	Edit Del

Editing: large-numbers.js (2.18 KB)

'use strict'
// Tar can encode large and negative numbers using a leading byte of
// 0xff for negative, and 0x80 for positive.

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
}

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.slice(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
}

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

module.exports = {
  encode,
  parse,
}