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<?php |
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/** |
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* SCSSPHP |
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* |
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* @copyright 2012-2020 Leaf Corcoran |
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* |
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* @license http://opensource.org/licenses/MIT MIT |
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* |
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* @link http://scssphp.github.io/scssphp |
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*/ |
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namespace ScssPhp\ScssPhp\SourceMap; |
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use ScssPhp\ScssPhp\SourceMap\Base64; |
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/** |
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* Base 64 VLQ |
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* |
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* Based on the Base 64 VLQ implementation in Closure Compiler: |
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* https://github.com/google/closure-compiler/blob/master/src/com/google/debugging/sourcemap/Base64VLQ.java |
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* |
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* Copyright 2011 The Closure Compiler Authors. |
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* |
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* Licensed under the Apache License, Version 2.0 (the "License"); |
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* you may not use this file except in compliance with the License. |
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* You may obtain a copy of the License at |
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* |
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* http://www.apache.org/licenses/LICENSE-2.0 |
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* |
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* Unless required by applicable law or agreed to in writing, software |
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* distributed under the License is distributed on an "AS IS" BASIS, |
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
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* See the License for the specific language governing permissions and |
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* limitations under the License. |
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* |
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* @author John Lenz <[email protected]> |
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* @author Anthon Pang <[email protected]> |
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*/ |
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class Base64VLQ |
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{ |
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// A Base64 VLQ digit can represent 5 bits, so it is base-32. |
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const VLQ_BASE_SHIFT = 5; |
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// A mask of bits for a VLQ digit (11111), 31 decimal. |
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const VLQ_BASE_MASK = 31; |
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// The continuation bit is the 6th bit. |
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const VLQ_CONTINUATION_BIT = 32; |
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/** |
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* Returns the VLQ encoded value. |
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* |
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* @param integer $value |
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* |
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* @return string |
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*/ |
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public static function encode($value) |
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{ |
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$encoded = ''; |
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$vlq = self::toVLQSigned($value); |
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do { |
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$digit = $vlq & self::VLQ_BASE_MASK; |
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//$vlq >>>= self::VLQ_BASE_SHIFT; // unsigned right shift |
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$vlq = (($vlq >> 1) & PHP_INT_MAX) >> (self::VLQ_BASE_SHIFT - 1); |
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if ($vlq > 0) { |
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$digit |= self::VLQ_CONTINUATION_BIT; |
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} |
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$encoded .= Base64::encode($digit); |
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} while ($vlq > 0); |
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return $encoded; |
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} |
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/** |
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* Decodes VLQValue. |
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* |
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* @param string $str |
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* @param integer $index |
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* |
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* @return integer |
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*/ |
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public static function decode($str, &$index) |
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{ |
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$result = 0; |
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$shift = 0; |
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do { |
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$c = $str[$index++]; |
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$digit = Base64::decode($c); |
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$continuation = ($digit & self::VLQ_CONTINUATION_BIT) != 0; |
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$digit &= self::VLQ_BASE_MASK; |
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$result = $result + ($digit << $shift); |
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$shift = $shift + self::VLQ_BASE_SHIFT; |
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} while ($continuation); |
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return self::fromVLQSigned($result); |
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} |
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/** |
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* Converts from a two-complement value to a value where the sign bit is |
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* is placed in the least significant bit. For example, as decimals: |
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* 1 becomes 2 (10 binary), -1 becomes 3 (11 binary) |
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* 2 becomes 4 (100 binary), -2 becomes 5 (101 binary) |
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* |
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* @param integer $value |
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* |
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* @return integer |
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*/ |
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private static function toVLQSigned($value) |
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{ |
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if ($value < 0) { |
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return ((-$value) << 1) + 1; |
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} |
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return ($value << 1) + 0; |
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} |
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/** |
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* Converts to a two-complement value from a value where the sign bit is |
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* is placed in the least significant bit. For example, as decimals: |
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* 2 (10 binary) becomes 1, 3 (11 binary) becomes -1 |
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* 4 (100 binary) becomes 2, 5 (101 binary) becomes -2 |
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* |
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* @param integer $value |
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* |
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* @return integer |
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*/ |
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private static function fromVLQSigned($value) |
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{ |
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$negate = ($value & 1) === 1; |
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//$value >>>= 1; // unsigned right shift |
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$value = ($value >> 1) & PHP_INT_MAX; |
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if (! $negate) { |
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return $value; |
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} |
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// We need to OR 0x80000000 here to ensure the 32nd bit (the sign bit) is |
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// always set for negative numbers. If `value` were 1, (meaning `negate` is |
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// true and all other bits were zeros), `value` would now be 0. -0 is just |
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// 0, and doesn't flip the 32nd bit as intended. All positive numbers will |
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// successfully flip the 32nd bit without issue, so it's a noop for them. |
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return -$value | 0x80000000; |
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} |
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} |
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