Roll Observatory packages and add a roll script

source_maps/lib/src/vlq.dart

-// Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
-// for details. All rights reserved. Use of this source code is governed by a
-// BSD-style license that can be found in the LICENSE file.
-
-
-/// Utilities to encode and decode VLQ values used in source maps.
-///
-/// Sourcemaps are encoded with variable length numbers as base64 encoded
-/// strings with the least significant digit coming first. Each base64 digit
-/// encodes a 5-bit value (0-31) and a continuation bit. Signed values can be
-/// represented by using the least significant bit of the value as the sign bit.
-///
-/// For more details see the source map [version 3 documentation][spec].
-/// [spec]: https://docs.google.com/a/google.com/document/d/1U1RGAehQwRypUTovF1KRlpiOFze0b-_2gc6fAH0KY0k/edit
-library source_maps.src.vlq;
-
-import 'dart:math';
-
-const int VLQ_BASE_SHIFT = 5;
-
-const int VLQ_BASE_MASK = (1 << 5) - 1;
-
-const int VLQ_CONTINUATION_BIT = 1 << 5;
-
-const int VLQ_CONTINUATION_MASK = 1 << 5;
-
-const String BASE64_DIGITS =
-    'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/';
-
-final Map<String, int> _digits = () {
-  var map = <String, int>{};
-  for (int i = 0; i < 64; i++) {
-    map[BASE64_DIGITS[i]] = i;
-  }
-  return map;
-}();
-
-final int MAX_INT32 = pow(2, 31) - 1;
-final int MIN_INT32 = -pow(2, 31);
-
-/// Creates the VLQ encoding of [value] as a sequence of characters
-Iterable<String> encodeVlq(int value) {
-  if (value < MIN_INT32 || value > MAX_INT32) {
-    throw new ArgumentError('expected 32 bit int, got: $value');
-  }
-  var res = <String>[];
-  int signBit = 0;
-  if (value < 0) {
-    signBit = 1;
-    value = -value;
-  }
-  value = (value << 1) | signBit;
-  do {
-    int digit = value & VLQ_BASE_MASK;
-    value >>= VLQ_BASE_SHIFT;
-    if (value > 0) {
-      digit |= VLQ_CONTINUATION_BIT;
-    }
-    res.add(BASE64_DIGITS[digit]);
-  } while (value > 0);
-  return res;
-}
-
-/// Decodes a value written as a sequence of VLQ characters. The first input
-/// character will be `chars.current` after calling `chars.moveNext` once. The
-/// iterator is advanced until a stop character is found (a character without
-/// the [VLQ_CONTINUATION_BIT]).
-int decodeVlq(Iterator<String> chars) {
-  int result = 0;
-  bool stop = false;
-  int shift = 0;
-  while (!stop) {
-    if (!chars.moveNext()) throw new StateError('incomplete VLQ value');
-    var char = chars.current;
-    if (!_digits.containsKey(char)) {
-      throw new FormatException('invalid character in VLQ encoding: $char');
-    }
-    var digit = _digits[char];
-    stop = (digit & VLQ_CONTINUATION_BIT) == 0;
-    digit &= VLQ_BASE_MASK;
-    result += (digit << shift);
-    shift += VLQ_BASE_SHIFT;
-  }
-
-  // Result uses the least significant bit as a sign bit. We convert it into a
-  // two-complement value. For example,
-  //   2 (10 binary) becomes 1
-  //   3 (11 binary) becomes -1
-  //   4 (100 binary) becomes 2
-  //   5 (101 binary) becomes -2
-  //   6 (110 binary) becomes 3
-  //   7 (111 binary) becomes -3
-  bool negate = (result & 1) == 1;
-  result = result >> 1;
-  result = negate ? -result : result;
-
-  // TODO(sigmund): can we detect this earlier?
-  if (result < MIN_INT32 || result > MAX_INT32) {
-    throw new FormatException(
-        'expected an encoded 32 bit int, but we got: $result');
-  }
-  return result;
-}