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<?php
/**
* Encode / Decode Base64 VLQ.
*
* @private
*/
class Less_SourceMap_Base64VLQ {
/**
* Shift
*
* @var int
*/
private $shift = 5;
/**
* Mask
*
* @var int
*/
private $mask = 0x1F; // == (1 << shift) == 0b00011111
/**
* Continuation bit
*
* @var int
*/
private $continuationBit = 0x20; // == (mask - 1 ) == 0b00100000
/**
* Char to integer map
*
* @var array
*/
private $charToIntMap = [
'A' => 0, 'B' => 1, 'C' => 2, 'D' => 3, 'E' => 4, 'F' => 5, 'G' => 6,
'H' => 7,'I' => 8, 'J' => 9, 'K' => 10, 'L' => 11, 'M' => 12, 'N' => 13,
'O' => 14, 'P' => 15, 'Q' => 16, 'R' => 17, 'S' => 18, 'T' => 19, 'U' => 20,
'V' => 21, 'W' => 22, 'X' => 23, 'Y' => 24, 'Z' => 25, 'a' => 26, 'b' => 27,
'c' => 28, 'd' => 29, 'e' => 30, 'f' => 31, 'g' => 32, 'h' => 33, 'i' => 34,
'j' => 35, 'k' => 36, 'l' => 37, 'm' => 38, 'n' => 39, 'o' => 40, 'p' => 41,
'q' => 42, 'r' => 43, 's' => 44, 't' => 45, 'u' => 46, 'v' => 47, 'w' => 48,
'x' => 49, 'y' => 50, 'z' => 51, 0 => 52, 1 => 53, 2 => 54, 3 => 55, 4 => 56,
5 => 57, 6 => 58, 7 => 59, 8 => 60, 9 => 61, '+' => 62, '/' => 63,
];
/**
* Integer to char map
*
* @var array
*/
private $intToCharMap = [
0 => 'A', 1 => 'B', 2 => 'C', 3 => 'D', 4 => 'E', 5 => 'F', 6 => 'G',
7 => 'H', 8 => 'I', 9 => 'J', 10 => 'K', 11 => 'L', 12 => 'M', 13 => 'N',
14 => 'O', 15 => 'P', 16 => 'Q', 17 => 'R', 18 => 'S', 19 => 'T', 20 => 'U',
21 => 'V', 22 => 'W', 23 => 'X', 24 => 'Y', 25 => 'Z', 26 => 'a', 27 => 'b',
28 => 'c', 29 => 'd', 30 => 'e', 31 => 'f', 32 => 'g', 33 => 'h', 34 => 'i',
35 => 'j', 36 => 'k', 37 => 'l', 38 => 'm', 39 => 'n', 40 => 'o', 41 => 'p',
42 => 'q', 43 => 'r', 44 => 's', 45 => 't', 46 => 'u', 47 => 'v', 48 => 'w',
49 => 'x', 50 => 'y', 51 => 'z', 52 => '0', 53 => '1', 54 => '2', 55 => '3',
56 => '4', 57 => '5', 58 => '6', 59 => '7', 60 => '8', 61 => '9', 62 => '+',
63 => '/',
];
/**
* Constructor
*/
public function __construct() {
// I leave it here for future reference
// foreach(str_split('ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/') as $i => $char)
// {
// $this->charToIntMap[$char] = $i;
// $this->intToCharMap[$i] = $char;
// }
}
/**
* Convert 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)
* We generate the value for 32 bit machines, hence -2147483648 becomes 1, not 4294967297,
* even on a 64 bit machine.
* @param int $aValue
*/
public function toVLQSigned( $aValue ) {
return 0xffffffff & ( $aValue < 0 ? ( ( -$aValue ) << 1 ) + 1 : ( $aValue << 1 ) + 0 );
}
/**
* Convert 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
* We assume that the value was generated with a 32 bit machine in mind.
* Hence
* 1 becomes -2147483648
* even on a 64 bit machine.
* @param int $aValue
*/
public function fromVLQSigned( $aValue ) {
return $aValue & 1 ? $this->zeroFill( ~$aValue + 2, 1 ) | ( -1 - 0x7fffffff ) : $this->zeroFill( $aValue, 1 );
}
/**
* Return the base 64 VLQ encoded value.
*
* @param int $aValue The value to encode
* @return string The encoded value
*/
public function encode( $aValue ) {
$encoded = '';
$vlq = $this->toVLQSigned( $aValue );
do
{
$digit = $vlq & $this->mask;
$vlq = $this->zeroFill( $vlq, $this->shift );
if ( $vlq > 0 ) {
$digit |= $this->continuationBit;
}
$encoded .= $this->base64Encode( $digit );
} while ( $vlq > 0 );
return $encoded;
}
/**
* Return the value decoded from base 64 VLQ.
*
* @param string $encoded The encoded value to decode
* @return int The decoded value
*/
public function decode( $encoded ) {
$vlq = 0;
$i = 0;
do
{
$digit = $this->base64Decode( $encoded[$i] );
$vlq |= ( $digit & $this->mask ) << ( $i * $this->shift );
$i++;
} while ( $digit & $this->continuationBit );
return $this->fromVLQSigned( $vlq );
}
/**
* Right shift with zero fill.
*
* @param int $a number to shift
* @param int $b number of bits to shift
* @return int
*/
public function zeroFill( $a, $b ) {
return ( $a >= 0 ) ? ( $a >> $b ) : ( $a >> $b ) & ( PHP_INT_MAX >> ( $b - 1 ) );
}
/**
* Encode single 6-bit digit as base64.
*
* @param int $number
* @return string
* @throws Exception If the number is invalid
*/
public function base64Encode( $number ) {
if ( $number < 0 || $number > 63 ) {
throw new Exception( sprintf( 'Invalid number "%s" given. Must be between 0 and 63.', (string)$number ) );
}
return $this->intToCharMap[$number];
}
/**
* Decode single 6-bit digit from base64
*
* @param string $char
* @return int
* @throws Exception If the number is invalid
*/
public function base64Decode( $char ) {
if ( !array_key_exists( $char, $this->charToIntMap ) ) {
throw new Exception( sprintf( 'Invalid base 64 digit "%s" given.', $char ) );
}
return $this->charToIntMap[$char];
}
}
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