LCOV - code coverage report
Current view: top level - source_maps-0.10.4/lib/src - vlq.dart (source / functions) Hit Total Coverage
Test: coverage.lcov Lines: 0 27 0.0 %
Date: 2017-10-10 20:17:03 Functions: 0 0 -

          Line data    Source code
       1             : // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
       2             : // for details. All rights reserved. Use of this source code is governed by a
       3             : // BSD-style license that can be found in the LICENSE file.
       4             : 
       5             : 
       6             : /// Utilities to encode and decode VLQ values used in source maps.
       7             : ///
       8             : /// Sourcemaps are encoded with variable length numbers as base64 encoded
       9             : /// strings with the least significant digit coming first. Each base64 digit
      10             : /// encodes a 5-bit value (0-31) and a continuation bit. Signed values can be
      11             : /// represented by using the least significant bit of the value as the sign bit.
      12             : ///
      13             : /// For more details see the source map [version 3 documentation][spec].
      14             : /// [spec]: https://docs.google.com/a/google.com/document/d/1U1RGAehQwRypUTovF1KRlpiOFze0b-_2gc6fAH0KY0k/edit
      15             : library source_maps.src.vlq;
      16             : 
      17             : import 'dart:math';
      18             : 
      19             : const int VLQ_BASE_SHIFT = 5;
      20             : 
      21             : const int VLQ_BASE_MASK = (1 << 5) - 1;
      22             : 
      23             : const int VLQ_CONTINUATION_BIT = 1 << 5;
      24             : 
      25             : const int VLQ_CONTINUATION_MASK = 1 << 5;
      26             : 
      27             : const String BASE64_DIGITS =
      28             :     'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/';
      29             : 
      30             : final Map<String, int> _digits = () {
      31             :   var map = <String, int>{};
      32             :   for (int i = 0; i < 64; i++) {
      33             :     map[BASE64_DIGITS[i]] = i;
      34             :   }
      35             :   return map;
      36             : }();
      37             : 
      38             : final int MAX_INT32 = pow(2, 31) - 1;
      39             : final int MIN_INT32 = -pow(2, 31);
      40             : 
      41             : /// Creates the VLQ encoding of [value] as a sequence of characters
      42             : Iterable<String> encodeVlq(int value) {
      43           0 :   if (value < MIN_INT32 || value > MAX_INT32) {
      44           0 :     throw new ArgumentError('expected 32 bit int, got: $value');
      45             :   }
      46           0 :   var res = <String>[];
      47             :   int signBit = 0;
      48           0 :   if (value < 0) {
      49             :     signBit = 1;
      50           0 :     value = -value;
      51             :   }
      52           0 :   value = (value << 1) | signBit;
      53             :   do {
      54           0 :     int digit = value & VLQ_BASE_MASK;
      55           0 :     value >>= VLQ_BASE_SHIFT;
      56           0 :     if (value > 0) {
      57           0 :       digit |= VLQ_CONTINUATION_BIT;
      58             :     }
      59           0 :     res.add(BASE64_DIGITS[digit]);
      60           0 :   } while (value > 0);
      61             :   return res;
      62             : }
      63             : 
      64             : /// Decodes a value written as a sequence of VLQ characters. The first input
      65             : /// character will be `chars.current` after calling `chars.moveNext` once. The
      66             : /// iterator is advanced until a stop character is found (a character without
      67             : /// the [VLQ_CONTINUATION_BIT]).
      68             : int decodeVlq(Iterator<String> chars) {
      69             :   int result = 0;
      70             :   bool stop = false;
      71             :   int shift = 0;
      72             :   while (!stop) {
      73           0 :     if (!chars.moveNext()) throw new StateError('incomplete VLQ value');
      74           0 :     var char = chars.current;
      75           0 :     if (!_digits.containsKey(char)) {
      76           0 :       throw new FormatException('invalid character in VLQ encoding: $char');
      77             :     }
      78           0 :     var digit = _digits[char];
      79           0 :     stop = (digit & VLQ_CONTINUATION_BIT) == 0;
      80           0 :     digit &= VLQ_BASE_MASK;
      81           0 :     result += (digit << shift);
      82           0 :     shift += VLQ_BASE_SHIFT;
      83             :   }
      84             : 
      85             :   // Result uses the least significant bit as a sign bit. We convert it into a
      86             :   // two-complement value. For example,
      87             :   //   2 (10 binary) becomes 1
      88             :   //   3 (11 binary) becomes -1
      89             :   //   4 (100 binary) becomes 2
      90             :   //   5 (101 binary) becomes -2
      91             :   //   6 (110 binary) becomes 3
      92             :   //   7 (111 binary) becomes -3
      93           0 :   bool negate = (result & 1) == 1;
      94           0 :   result = result >> 1;
      95           0 :   result = negate ? -result : result;
      96             : 
      97             :   // TODO(sigmund): can we detect this earlier?
      98           0 :   if (result < MIN_INT32 || result > MAX_INT32) {
      99           0 :     throw new FormatException(
     100           0 :         'expected an encoded 32 bit int, but we got: $result');
     101             :   }
     102             :   return result;
     103             : }

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