* first action! (#1)

node_modules/tar/lib/large-numbers.js

@@ -0,0 +1,97 @@
+'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