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