| <?php |
| |
| /** |
| * FixedBitNotation |
| * |
| * @author Andre DeMarre |
| * @package FixedBitNotation |
| */ |
| |
| /** |
| * The FixedBitNotation class is for binary to text conversion. It |
| * can handle many encoding schemes, formally defined or not, that |
| * use a fixed number of bits to encode each character. |
| * |
| * @package FixedBitNotation |
| */ |
| class FixedBitNotation |
| { |
| protected $_chars; |
| protected $_bitsPerCharacter; |
| protected $_radix; |
| protected $_rightPadFinalBits; |
| protected $_padFinalGroup; |
| protected $_padCharacter; |
| protected $_charmap; |
| |
| /** |
| * Constructor |
| * |
| * @param integer $bitsPerCharacter Bits to use for each encoded |
| * character |
| * @param string $chars Base character alphabet |
| * @param boolean $rightPadFinalBits How to encode last character |
| * @param boolean $padFinalGroup Add padding to end of encoded |
| * output |
| * @param string $padCharacter Character to use for padding |
| */ |
| public function __construct( |
| $bitsPerCharacter, $chars = NULL, $rightPadFinalBits = FALSE, |
| $padFinalGroup = FALSE, $padCharacter = '=') |
| { |
| // Ensure validity of $chars |
| if (!is_string($chars) || ($charLength = strlen($chars)) < 2) { |
| $chars = |
| '0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ-,'; |
| $charLength = 64; |
| } |
| |
| // Ensure validity of $bitsPerCharacter |
| if ($bitsPerCharacter < 1) { |
| // $bitsPerCharacter must be at least 1 |
| $bitsPerCharacter = 1; |
| $radix = 2; |
| |
| } elseif ($charLength < 1 << $bitsPerCharacter) { |
| // Character length of $chars is too small for $bitsPerCharacter |
| // Set $bitsPerCharacter to greatest acceptable value |
| $bitsPerCharacter = 1; |
| $radix = 2; |
| |
| while ($charLength >= ($radix <<= 1) && $bitsPerCharacter < 8) { |
| $bitsPerCharacter++; |
| } |
| |
| $radix >>= 1; |
| |
| } elseif ($bitsPerCharacter > 8) { |
| // $bitsPerCharacter must not be greater than 8 |
| $bitsPerCharacter = 8; |
| $radix = 256; |
| |
| } else { |
| $radix = 1 << $bitsPerCharacter; |
| } |
| |
| $this->_chars = $chars; |
| $this->_bitsPerCharacter = $bitsPerCharacter; |
| $this->_radix = $radix; |
| $this->_rightPadFinalBits = $rightPadFinalBits; |
| $this->_padFinalGroup = $padFinalGroup; |
| $this->_padCharacter = $padCharacter[0]; |
| } |
| |
| /** |
| * Encode a string |
| * |
| * @param string $rawString Binary data to encode |
| * @return string |
| */ |
| public function encode($rawString) |
| { |
| // Unpack string into an array of bytes |
| $bytes = unpack('C*', $rawString); |
| $byteCount = count($bytes); |
| |
| $encodedString = ''; |
| $byte = array_shift($bytes); |
| $bitsRead = 0; |
| |
| $chars = $this->_chars; |
| $bitsPerCharacter = $this->_bitsPerCharacter; |
| $rightPadFinalBits = $this->_rightPadFinalBits; |
| $padFinalGroup = $this->_padFinalGroup; |
| $padCharacter = $this->_padCharacter; |
| |
| // Generate encoded output; |
| // each loop produces one encoded character |
| for ($c = 0; $c < $byteCount * 8 / $bitsPerCharacter; $c++) { |
| |
| // Get the bits needed for this encoded character |
| if ($bitsRead + $bitsPerCharacter > 8) { |
| // Not enough bits remain in this byte for the current |
| // character |
| // Save the remaining bits before getting the next byte |
| $oldBitCount = 8 - $bitsRead; |
| $oldBits = $byte ^ ($byte >> $oldBitCount << $oldBitCount); |
| $newBitCount = $bitsPerCharacter - $oldBitCount; |
| |
| if (!$bytes) { |
| // Last bits; match final character and exit loop |
| if ($rightPadFinalBits) $oldBits <<= $newBitCount; |
| $encodedString .= $chars[$oldBits]; |
| |
| if ($padFinalGroup) { |
| // Array of the lowest common multiples of |
| // $bitsPerCharacter and 8, divided by 8 |
| $lcmMap = array(1 => 1, 2 => 1, 3 => 3, 4 => 1, |
| 5 => 5, 6 => 3, 7 => 7, 8 => 1); |
| $bytesPerGroup = $lcmMap[$bitsPerCharacter]; |
| $pads = $bytesPerGroup * 8 / $bitsPerCharacter |
| - ceil((strlen($rawString) % $bytesPerGroup) |
| * 8 / $bitsPerCharacter); |
| $encodedString .= str_repeat($padCharacter[0], $pads); |
| } |
| |
| break; |
| } |
| |
| // Get next byte |
| $byte = array_shift($bytes); |
| $bitsRead = 0; |
| |
| } else { |
| $oldBitCount = 0; |
| $newBitCount = $bitsPerCharacter; |
| } |
| |
| // Read only the needed bits from this byte |
| $bits = $byte >> 8 - ($bitsRead + ($newBitCount)); |
| $bits ^= $bits >> $newBitCount << $newBitCount; |
| $bitsRead += $newBitCount; |
| |
| if ($oldBitCount) { |
| // Bits come from seperate bytes, add $oldBits to $bits |
| $bits = ($oldBits << $newBitCount) | $bits; |
| } |
| |
| $encodedString .= $chars[$bits]; |
| } |
| |
| return $encodedString; |
| } |
| |
| /** |
| * Decode a string |
| * |
| * @param string $encodedString Data to decode |
| * @param boolean $caseSensitive |
| * @param boolean $strict Returns NULL if $encodedString contains |
| * an undecodable character |
| * @return string|NULL |
| */ |
| public function decode($encodedString, $caseSensitive = TRUE, |
| $strict = FALSE) |
| { |
| if (!$encodedString || !is_string($encodedString)) { |
| // Empty string, nothing to decode |
| return ''; |
| } |
| |
| $chars = $this->_chars; |
| $bitsPerCharacter = $this->_bitsPerCharacter; |
| $radix = $this->_radix; |
| $rightPadFinalBits = $this->_rightPadFinalBits; |
| $padFinalGroup = $this->_padFinalGroup; |
| $padCharacter = $this->_padCharacter; |
| |
| // Get index of encoded characters |
| if ($this->_charmap) { |
| $charmap = $this->_charmap; |
| |
| } else { |
| $charmap = array(); |
| |
| for ($i = 0; $i < $radix; $i++) { |
| $charmap[$chars[$i]] = $i; |
| } |
| |
| $this->_charmap = $charmap; |
| } |
| |
| // The last encoded character is $encodedString[$lastNotatedIndex] |
| $lastNotatedIndex = strlen($encodedString) - 1; |
| |
| // Remove trailing padding characters |
| while ($encodedString[$lastNotatedIndex] == $padCharacter[0]) { |
| $encodedString = substr($encodedString, 0, $lastNotatedIndex); |
| $lastNotatedIndex--; |
| } |
| |
| $rawString = ''; |
| $byte = 0; |
| $bitsWritten = 0; |
| |
| // Convert each encoded character to a series of unencoded bits |
| for ($c = 0; $c <= $lastNotatedIndex; $c++) { |
| |
| if (!isset($charmap[$encodedString[$c]]) && !$caseSensitive) { |
| // Encoded character was not found; try other case |
| if (isset($charmap[$cUpper |
| = strtoupper($encodedString[$c])])) { |
| $charmap[$encodedString[$c]] = $charmap[$cUpper]; |
| |
| } elseif (isset($charmap[$cLower |
| = strtolower($encodedString[$c])])) { |
| $charmap[$encodedString[$c]] = $charmap[$cLower]; |
| } |
| } |
| |
| if (isset($charmap[$encodedString[$c]])) { |
| $bitsNeeded = 8 - $bitsWritten; |
| $unusedBitCount = $bitsPerCharacter - $bitsNeeded; |
| |
| // Get the new bits ready |
| if ($bitsNeeded > $bitsPerCharacter) { |
| // New bits aren't enough to complete a byte; shift them |
| // left into position |
| $newBits = $charmap[$encodedString[$c]] << $bitsNeeded |
| - $bitsPerCharacter; |
| $bitsWritten += $bitsPerCharacter; |
| |
| } elseif ($c != $lastNotatedIndex || $rightPadFinalBits) { |
| // Zero or more too many bits to complete a byte; |
| // shift right |
| $newBits = $charmap[$encodedString[$c]] >> $unusedBitCount; |
| $bitsWritten = 8; //$bitsWritten += $bitsNeeded; |
| |
| } else { |
| // Final bits don't need to be shifted |
| $newBits = $charmap[$encodedString[$c]]; |
| $bitsWritten = 8; |
| } |
| |
| $byte |= $newBits; |
| |
| if ($bitsWritten == 8 || $c == $lastNotatedIndex) { |
| // Byte is ready to be written |
| $rawString .= pack('C', $byte); |
| |
| if ($c != $lastNotatedIndex) { |
| // Start the next byte |
| $bitsWritten = $unusedBitCount; |
| $byte = ($charmap[$encodedString[$c]] |
| ^ ($newBits << $unusedBitCount)) << 8 - $bitsWritten; |
| } |
| } |
| |
| } elseif ($strict) { |
| // Unable to decode character; abort |
| return NULL; |
| } |
| } |
| |
| return $rawString; |
| } |
| } |