| 1 |
<?php |
| 2 |
|
| 3 |
/** |
| 4 |
* FixedBitNotation |
| 5 |
* |
| 6 |
* @author Andre DeMarre |
| 7 |
* @package FixedBitNotation |
| 8 |
*/ |
| 9 |
|
| 10 |
/** |
| 11 |
* The FixedBitNotation class is for binary to text conversion. It |
| 12 |
* can handle many encoding schemes, formally defined or not, that |
| 13 |
* use a fixed number of bits to encode each character. |
| 14 |
* |
| 15 |
* @package FixedBitNotation |
| 16 |
*/ |
| 17 |
class WebTotemFixedBitNotation |
| 18 |
{ |
| 19 |
protected $_chars; |
| 20 |
protected $_bitsPerCharacter; |
| 21 |
protected $_radix; |
| 22 |
protected $_rightPadFinalBits; |
| 23 |
protected $_padFinalGroup; |
| 24 |
protected $_padCharacter; |
| 25 |
protected $_charmap; |
| 26 |
|
| 27 |
/** |
| 28 |
* Constructor |
| 29 |
* |
| 30 |
* @param integer $bitsPerCharacter Bits to use for each encoded |
| 31 |
* character |
| 32 |
* @param string $chars Base character alphabet |
| 33 |
* @param boolean $rightPadFinalBits How to encode last character |
| 34 |
* @param boolean $padFinalGroup Add padding to end of encoded |
| 35 |
* output |
| 36 |
* @param string $padCharacter Character to use for padding |
| 37 |
*/ |
| 38 |
public function __construct( |
| 39 |
$bitsPerCharacter, $chars = NULL, $rightPadFinalBits = FALSE, |
| 40 |
$padFinalGroup = FALSE, $padCharacter = '=') |
| 41 |
{ |
| 42 |
// Ensure validity of $chars |
| 43 |
if (!is_string($chars) || ($charLength = strlen($chars)) < 2) { |
| 44 |
$chars = |
| 45 |
'0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ-,'; |
| 46 |
$charLength = 64; |
| 47 |
} |
| 48 |
|
| 49 |
// Ensure validity of $bitsPerCharacter |
| 50 |
if ($bitsPerCharacter < 1) { |
| 51 |
// $bitsPerCharacter must be at least 1 |
| 52 |
$bitsPerCharacter = 1; |
| 53 |
$radix = 2; |
| 54 |
|
| 55 |
} elseif ($charLength < 1 << $bitsPerCharacter) { |
| 56 |
// Character length of $chars is too small for $bitsPerCharacter |
| 57 |
// Set $bitsPerCharacter to greatest acceptable value |
| 58 |
$bitsPerCharacter = 1; |
| 59 |
$radix = 2; |
| 60 |
|
| 61 |
while ($charLength >= ($radix <<= 1) && $bitsPerCharacter < 8) { |
| 62 |
$bitsPerCharacter++; |
| 63 |
} |
| 64 |
|
| 65 |
$radix >>= 1; |
| 66 |
|
| 67 |
} elseif ($bitsPerCharacter > 8) { |
| 68 |
// $bitsPerCharacter must not be greater than 8 |
| 69 |
$bitsPerCharacter = 8; |
| 70 |
$radix = 256; |
| 71 |
|
| 72 |
} else { |
| 73 |
$radix = 1 << $bitsPerCharacter; |
| 74 |
} |
| 75 |
|
| 76 |
$this->_chars = $chars; |
| 77 |
$this->_bitsPerCharacter = $bitsPerCharacter; |
| 78 |
$this->_radix = $radix; |
| 79 |
$this->_rightPadFinalBits = $rightPadFinalBits; |
| 80 |
$this->_padFinalGroup = $padFinalGroup; |
| 81 |
$this->_padCharacter = $padCharacter[0]; |
| 82 |
} |
| 83 |
|
| 84 |
/** |
| 85 |
* Encode a string |
| 86 |
* |
| 87 |
* @param string $rawString Binary data to encode |
| 88 |
* @return string |
| 89 |
*/ |
| 90 |
public function encode($rawString) |
| 91 |
{ |
| 92 |
// Unpack string into an array of bytes |
| 93 |
$bytes = unpack('C*', $rawString); |
| 94 |
$byteCount = count($bytes); |
| 95 |
|
| 96 |
$encodedString = ''; |
| 97 |
$byte = array_shift($bytes); |
| 98 |
$bitsRead = 0; |
| 99 |
|
| 100 |
$chars = $this->_chars; |
| 101 |
$bitsPerCharacter = $this->_bitsPerCharacter; |
| 102 |
$rightPadFinalBits = $this->_rightPadFinalBits; |
| 103 |
$padFinalGroup = $this->_padFinalGroup; |
| 104 |
$padCharacter = $this->_padCharacter; |
| 105 |
|
| 106 |
// Generate encoded output; |
| 107 |
// each loop produces one encoded character |
| 108 |
for ($c = 0; $c < $byteCount * 8 / $bitsPerCharacter; $c++) { |
| 109 |
|
| 110 |
// Get the bits needed for this encoded character |
| 111 |
if ($bitsRead + $bitsPerCharacter > 8) { |
| 112 |
// Not enough bits remain in this byte for the current |
| 113 |
// character |
| 114 |
// Save the remaining bits before getting the next byte |
| 115 |
$oldBitCount = 8 - $bitsRead; |
| 116 |
$oldBits = $byte ^ ($byte >> $oldBitCount << $oldBitCount); |
| 117 |
$newBitCount = $bitsPerCharacter - $oldBitCount; |
| 118 |
|
| 119 |
if (!$bytes) { |
| 120 |
// Last bits; match final character and exit loop |
| 121 |
if ($rightPadFinalBits) $oldBits <<= $newBitCount; |
| 122 |
$encodedString .= $chars[$oldBits]; |
| 123 |
|
| 124 |
if ($padFinalGroup) { |
| 125 |
// Array of the lowest common multiples of |
| 126 |
// $bitsPerCharacter and 8, divided by 8 |
| 127 |
$lcmMap = array(1 => 1, 2 => 1, 3 => 3, 4 => 1, |
| 128 |
5 => 5, 6 => 3, 7 => 7, 8 => 1); |
| 129 |
$bytesPerGroup = $lcmMap[$bitsPerCharacter]; |
| 130 |
$pads = $bytesPerGroup * 8 / $bitsPerCharacter |
| 131 |
- ceil((strlen($rawString) % $bytesPerGroup) |
| 132 |
* 8 / $bitsPerCharacter); |
| 133 |
$encodedString .= str_repeat($padCharacter[0], $pads); |
| 134 |
} |
| 135 |
|
| 136 |
break; |
| 137 |
} |
| 138 |
|
| 139 |
// Get next byte |
| 140 |
$byte = array_shift($bytes); |
| 141 |
$bitsRead = 0; |
| 142 |
|
| 143 |
} else { |
| 144 |
$oldBitCount = 0; |
| 145 |
$newBitCount = $bitsPerCharacter; |
| 146 |
} |
| 147 |
|
| 148 |
// Read only the needed bits from this byte |
| 149 |
$bits = $byte >> 8 - ($bitsRead + ($newBitCount)); |
| 150 |
$bits ^= $bits >> $newBitCount << $newBitCount; |
| 151 |
$bitsRead += $newBitCount; |
| 152 |
|
| 153 |
if ($oldBitCount) { |
| 154 |
// Bits come from seperate bytes, add $oldBits to $bits |
| 155 |
$bits = ($oldBits << $newBitCount) | $bits; |
| 156 |
} |
| 157 |
|
| 158 |
$encodedString .= $chars[$bits]; |
| 159 |
} |
| 160 |
|
| 161 |
return $encodedString; |
| 162 |
} |
| 163 |
|
| 164 |
/** |
| 165 |
* Decode a string |
| 166 |
* |
| 167 |
* @param string $encodedString Data to decode |
| 168 |
* @param boolean $caseSensitive |
| 169 |
* @param boolean $strict Returns NULL if $encodedString contains |
| 170 |
* an undecodable character |
| 171 |
* @return string|NULL |
| 172 |
*/ |
| 173 |
public function decode($encodedString, $caseSensitive = TRUE, |
| 174 |
$strict = FALSE) |
| 175 |
{ |
| 176 |
if (!$encodedString || !is_string($encodedString)) { |
| 177 |
// Empty string, nothing to decode |
| 178 |
return ''; |
| 179 |
} |
| 180 |
|
| 181 |
$chars = $this->_chars; |
| 182 |
$bitsPerCharacter = $this->_bitsPerCharacter; |
| 183 |
$radix = $this->_radix; |
| 184 |
$rightPadFinalBits = $this->_rightPadFinalBits; |
| 185 |
$padFinalGroup = $this->_padFinalGroup; |
| 186 |
$padCharacter = $this->_padCharacter; |
| 187 |
|
| 188 |
// Get index of encoded characters |
| 189 |
if ($this->_charmap) { |
| 190 |
$charmap = $this->_charmap; |
| 191 |
|
| 192 |
} else { |
| 193 |
$charmap = array(); |
| 194 |
|
| 195 |
for ($i = 0; $i < $radix; $i++) { |
| 196 |
$charmap[$chars[$i]] = $i; |
| 197 |
} |
| 198 |
|
| 199 |
$this->_charmap = $charmap; |
| 200 |
} |
| 201 |
|
| 202 |
// The last encoded character is $encodedString[$lastNotatedIndex] |
| 203 |
$lastNotatedIndex = strlen($encodedString) - 1; |
| 204 |
|
| 205 |
// Remove trailing padding characters |
| 206 |
while ($encodedString[$lastNotatedIndex] == $padCharacter[0]) { |
| 207 |
$encodedString = substr($encodedString, 0, $lastNotatedIndex); |
| 208 |
$lastNotatedIndex--; |
| 209 |
} |
| 210 |
|
| 211 |
$rawString = ''; |
| 212 |
$byte = 0; |
| 213 |
$bitsWritten = 0; |
| 214 |
|
| 215 |
// Convert each encoded character to a series of unencoded bits |
| 216 |
for ($c = 0; $c <= $lastNotatedIndex; $c++) { |
| 217 |
|
| 218 |
if (!isset($charmap[$encodedString[$c]]) && !$caseSensitive) { |
| 219 |
// Encoded character was not found; try other case |
| 220 |
if (isset($charmap[$cUpper |
| 221 |
= strtoupper($encodedString[$c])])) { |
| 222 |
$charmap[$encodedString[$c]] = $charmap[$cUpper]; |
| 223 |
|
| 224 |
} elseif (isset($charmap[$cLower |
| 225 |
= strtolower($encodedString[$c])])) { |
| 226 |
$charmap[$encodedString[$c]] = $charmap[$cLower]; |
| 227 |
} |
| 228 |
} |
| 229 |
|
| 230 |
if (isset($charmap[$encodedString[$c]])) { |
| 231 |
$bitsNeeded = 8 - $bitsWritten; |
| 232 |
$unusedBitCount = $bitsPerCharacter - $bitsNeeded; |
| 233 |
|
| 234 |
// Get the new bits ready |
| 235 |
if ($bitsNeeded > $bitsPerCharacter) { |
| 236 |
// New bits aren't enough to complete a byte; shift them |
| 237 |
// left into position |
| 238 |
$newBits = $charmap[$encodedString[$c]] << $bitsNeeded |
| 239 |
- $bitsPerCharacter; |
| 240 |
$bitsWritten += $bitsPerCharacter; |
| 241 |
|
| 242 |
} elseif ($c != $lastNotatedIndex || $rightPadFinalBits) { |
| 243 |
// Zero or more too many bits to complete a byte; |
| 244 |
// shift right |
| 245 |
$newBits = $charmap[$encodedString[$c]] >> $unusedBitCount; |
| 246 |
$bitsWritten = 8; //$bitsWritten += $bitsNeeded; |
| 247 |
|
| 248 |
} else { |
| 249 |
// Final bits don't need to be shifted |
| 250 |
$newBits = $charmap[$encodedString[$c]]; |
| 251 |
$bitsWritten = 8; |
| 252 |
} |
| 253 |
|
| 254 |
$byte |= $newBits; |
| 255 |
|
| 256 |
if ($bitsWritten == 8 || $c == $lastNotatedIndex) { |
| 257 |
// Byte is ready to be written |
| 258 |
$rawString .= pack('C', $byte); |
| 259 |
|
| 260 |
if ($c != $lastNotatedIndex) { |
| 261 |
// Start the next byte |
| 262 |
$bitsWritten = $unusedBitCount; |
| 263 |
$byte = ($charmap[$encodedString[$c]] |
| 264 |
^ ($newBits << $unusedBitCount)) << 8 - $bitsWritten; |
| 265 |
} |
| 266 |
} |
| 267 |
|
| 268 |
} elseif ($strict) { |
| 269 |
// Unable to decode character; abort |
| 270 |
return NULL; |
| 271 |
} |
| 272 |
} |
| 273 |
|
| 274 |
return $rawString; |
| 275 |
} |
| 276 |
} |
| 277 |
|
