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Diffstat (limited to 'node_modules/source-map/lib/base64-vlq.js')
-rw-r--r-- | node_modules/source-map/lib/base64-vlq.js | 140 |
1 files changed, 140 insertions, 0 deletions
diff --git a/node_modules/source-map/lib/base64-vlq.js b/node_modules/source-map/lib/base64-vlq.js new file mode 100644 index 0000000..612b404 --- /dev/null +++ b/node_modules/source-map/lib/base64-vlq.js @@ -0,0 +1,140 @@ +/* -*- Mode: js; js-indent-level: 2; -*- */ +/* + * Copyright 2011 Mozilla Foundation and contributors + * Licensed under the New BSD license. See LICENSE or: + * http://opensource.org/licenses/BSD-3-Clause + * + * Based on the Base 64 VLQ implementation in Closure Compiler: + * https://code.google.com/p/closure-compiler/source/browse/trunk/src/com/google/debugging/sourcemap/Base64VLQ.java + * + * Copyright 2011 The Closure Compiler Authors. All rights reserved. + * Redistribution and use in source and binary forms, with or without + * modification, are permitted provided that the following conditions are + * met: + * + * * Redistributions of source code must retain the above copyright + * notice, this list of conditions and the following disclaimer. + * * Redistributions in binary form must reproduce the above + * copyright notice, this list of conditions and the following + * disclaimer in the documentation and/or other materials provided + * with the distribution. + * * Neither the name of Google Inc. nor the names of its + * contributors may be used to endorse or promote products derived + * from this software without specific prior written permission. + * + * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS + * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT + * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR + * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT + * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, + * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT + * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, + * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY + * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT + * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE + * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. + */ + +var base64 = require('./base64'); + +// A single base 64 digit can contain 6 bits of data. For the base 64 variable +// length quantities we use in the source map spec, the first bit is the sign, +// the next four bits are the actual value, and the 6th bit is the +// continuation bit. The continuation bit tells us whether there are more +// digits in this value following this digit. +// +// Continuation +// | Sign +// | | +// V V +// 101011 + +var VLQ_BASE_SHIFT = 5; + +// binary: 100000 +var VLQ_BASE = 1 << VLQ_BASE_SHIFT; + +// binary: 011111 +var VLQ_BASE_MASK = VLQ_BASE - 1; + +// binary: 100000 +var VLQ_CONTINUATION_BIT = VLQ_BASE; + +/** + * Converts from a two-complement value to a value where the sign bit is + * placed in the least significant bit. For example, as decimals: + * 1 becomes 2 (10 binary), -1 becomes 3 (11 binary) + * 2 becomes 4 (100 binary), -2 becomes 5 (101 binary) + */ +function toVLQSigned(aValue) { + return aValue < 0 + ? ((-aValue) << 1) + 1 + : (aValue << 1) + 0; +} + +/** + * Converts to a two-complement value from a value where the sign bit is + * placed in the least significant bit. For example, as decimals: + * 2 (10 binary) becomes 1, 3 (11 binary) becomes -1 + * 4 (100 binary) becomes 2, 5 (101 binary) becomes -2 + */ +function fromVLQSigned(aValue) { + var isNegative = (aValue & 1) === 1; + var shifted = aValue >> 1; + return isNegative + ? -shifted + : shifted; +} + +/** + * Returns the base 64 VLQ encoded value. + */ +exports.encode = function base64VLQ_encode(aValue) { + var encoded = ""; + var digit; + + var vlq = toVLQSigned(aValue); + + do { + digit = vlq & VLQ_BASE_MASK; + vlq >>>= VLQ_BASE_SHIFT; + if (vlq > 0) { + // There are still more digits in this value, so we must make sure the + // continuation bit is marked. + digit |= VLQ_CONTINUATION_BIT; + } + encoded += base64.encode(digit); + } while (vlq > 0); + + return encoded; +}; + +/** + * Decodes the next base 64 VLQ value from the given string and returns the + * value and the rest of the string via the out parameter. + */ +exports.decode = function base64VLQ_decode(aStr, aIndex, aOutParam) { + var strLen = aStr.length; + var result = 0; + var shift = 0; + var continuation, digit; + + do { + if (aIndex >= strLen) { + throw new Error("Expected more digits in base 64 VLQ value."); + } + + digit = base64.decode(aStr.charCodeAt(aIndex++)); + if (digit === -1) { + throw new Error("Invalid base64 digit: " + aStr.charAt(aIndex - 1)); + } + + continuation = !!(digit & VLQ_CONTINUATION_BIT); + digit &= VLQ_BASE_MASK; + result = result + (digit << shift); + shift += VLQ_BASE_SHIFT; + } while (continuation); + + aOutParam.value = fromVLQSigned(result); + aOutParam.rest = aIndex; +}; |