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1<?php
2
3/**
4 * Class for converting between different unit-lengths as specified by
5 * CSS.
6 */
7class HTMLPurifier_UnitConverter
8{
9
10 const ENGLISH = 1;
11 const METRIC = 2;
12 const DIGITAL = 3;
13
14 /**
15 * Units information array. Units are grouped into measuring systems
16 * (English, Metric), and are assigned an integer representing
17 * the conversion factor between that unit and the smallest unit in
18 * the system. Numeric indexes are actually magical constants that
19 * encode conversion data from one system to the next, with a O(n^2)
20 * constraint on memory (this is generally not a problem, since
21 * the number of measuring systems is small.)
22 */
23 protected static $units = array(
24 self::ENGLISH => array(
25 'px' => 3, // This is as per CSS 2.1 and Firefox. Your mileage may vary
26 'pt' => 4,
27 'pc' => 48,
28 'in' => 288,
29 self::METRIC => array('pt', '0.352777778', 'mm'),
30 ),
31 self::METRIC => array(
32 'mm' => 1,
33 'cm' => 10,
34 self::ENGLISH => array('mm', '2.83464567', 'pt'),
35 ),
36 );
37
38 /**
39 * Minimum bcmath precision for output.
40 * @type int
41 */
42 protected $outputPrecision;
43
44 /**
45 * Bcmath precision for internal calculations.
46 * @type int
47 */
48 protected $internalPrecision;
49
50 /**
51 * Whether or not BCMath is available.
52 * @type bool
53 */
54 private $bcmath;
55
56 public function __construct($output_precision = 4, $internal_precision = 10, $force_no_bcmath = false)
57 {
58 $this->outputPrecision = $output_precision;
59 $this->internalPrecision = $internal_precision;
60 $this->bcmath = !$force_no_bcmath && function_exists('bcmul');
61 }
62
63 /**
64 * Converts a length object of one unit into another unit.
65 * @param HTMLPurifier_Length $length
66 * Instance of HTMLPurifier_Length to convert. You must validate()
67 * it before passing it here!
68 * @param string $to_unit
69 * Unit to convert to.
70 * @return HTMLPurifier_Length|bool
71 * @note
72 * About precision: This conversion function pays very special
73 * attention to the incoming precision of values and attempts
74 * to maintain a number of significant figure. Results are
75 * fairly accurate up to nine digits. Some caveats:
76 * - If a number is zero-padded as a result of this significant
77 * figure tracking, the zeroes will be eliminated.
78 * - If a number contains less than four sigfigs ($outputPrecision)
79 * and this causes some decimals to be excluded, those
80 * decimals will be added on.
81 */
82 public function convert($length, $to_unit)
83 {
84 if (!$length->isValid()) {
85 return false;
86 }
87
88 $n = $length->getN();
89 $unit = $length->getUnit();
90
91 if ($n === '0' || $unit === false) {
92 return new HTMLPurifier_Length('0', false);
93 }
94
95 $state = $dest_state = false;
96 foreach (self::$units as $k => $x) {
97 if (isset($x[$unit])) {
98 $state = $k;
99 }
100 if (isset($x[$to_unit])) {
101 $dest_state = $k;
102 }
103 }
104 if (!$state || !$dest_state) {
105 return false;
106 }
107
108 // Some calculations about the initial precision of the number;
109 // this will be useful when we need to do final rounding.
110 $sigfigs = $this->getSigFigs($n);
111 if ($sigfigs < $this->outputPrecision) {
112 $sigfigs = $this->outputPrecision;
113 }
114
115 // BCMath's internal precision deals only with decimals. Use
116 // our default if the initial number has no decimals, or increase
117 // it by how ever many decimals, thus, the number of guard digits
118 // will always be greater than or equal to internalPrecision.
119 $log = (int)floor(log(abs($n), 10));
120 $cp = ($log < 0) ? $this->internalPrecision - $log : $this->internalPrecision; // internal precision
121
122 for ($i = 0; $i < 2; $i++) {
123
124 // Determine what unit IN THIS SYSTEM we need to convert to
125 if ($dest_state === $state) {
126 // Simple conversion
127 $dest_unit = $to_unit;
128 } else {
129 // Convert to the smallest unit, pending a system shift
130 $dest_unit = self::$units[$state][$dest_state][0];
131 }
132
133 // Do the conversion if necessary
134 if ($dest_unit !== $unit) {
135 $factor = $this->div(self::$units[$state][$unit], self::$units[$state][$dest_unit], $cp);
136 $n = $this->mul($n, $factor, $cp);
137 $unit = $dest_unit;
138 }
139
140 // Output was zero, so bail out early. Shouldn't ever happen.
141 if ($n === '') {
142 $n = '0';
143 $unit = $to_unit;
144 break;
145 }
146
147 // It was a simple conversion, so bail out
148 if ($dest_state === $state) {
149 break;
150 }
151
152 if ($i !== 0) {
153 // Conversion failed! Apparently, the system we forwarded
154 // to didn't have this unit. This should never happen!
155 return false;
156 }
157
158 // Pre-condition: $i == 0
159
160 // Perform conversion to next system of units
161 $n = $this->mul($n, self::$units[$state][$dest_state][1], $cp);
162 $unit = self::$units[$state][$dest_state][2];
163 $state = $dest_state;
164
165 // One more loop around to convert the unit in the new system.
166
167 }
168
169 // Post-condition: $unit == $to_unit
170 if ($unit !== $to_unit) {
171 return false;
172 }
173
174 // Useful for debugging:
175 //echo "<pre>n";
176 //echo "$n\nsigfigs = $sigfigs\nnew_log = $new_log\nlog = $log\nrp = $rp\n</pre>\n";
177
178 $n = $this->round($n, $sigfigs);
179 if (strpos($n, '.') !== false) {
180 $n = rtrim($n, '0');
181 }
182 $n = rtrim($n, '.');
183
184 return new HTMLPurifier_Length($n, $unit);
185 }
186
187 /**
188 * Returns the number of significant figures in a string number.
189 * @param string $n Decimal number
190 * @return int number of sigfigs
191 */
192 public function getSigFigs($n)
193 {
194 $n = ltrim($n, '0+-');
195 $dp = strpos($n, '.'); // decimal position
196 if ($dp === false) {
197 $sigfigs = strlen(rtrim($n, '0'));
198 } else {
199 $sigfigs = strlen(ltrim($n, '0.')); // eliminate extra decimal character
200 if ($dp !== 0) {
201 $sigfigs--;
202 }
203 }
204 return $sigfigs;
205 }
206
207 /**
208 * Adds two numbers, using arbitrary precision when available.
209 * @param string $s1
210 * @param string $s2
211 * @param int $scale
212 * @return string
213 */
214 private function add($s1, $s2, $scale)
215 {
216 if ($this->bcmath) {
217 return bcadd($s1, $s2, $scale);
218 } else {
219 return $this->scale((float)$s1 + (float)$s2, $scale);
220 }
221 }
222
223 /**
224 * Multiples two numbers, using arbitrary precision when available.
225 * @param string $s1
226 * @param string $s2
227 * @param int $scale
228 * @return string
229 */
230 private function mul($s1, $s2, $scale)
231 {
232 if ($this->bcmath) {
233 return bcmul($s1, $s2, $scale);
234 } else {
235 return $this->scale((float)$s1 * (float)$s2, $scale);
236 }
237 }
238
239 /**
240 * Divides two numbers, using arbitrary precision when available.
241 * @param string $s1
242 * @param string $s2
243 * @param int $scale
244 * @return string
245 */
246 private function div($s1, $s2, $scale)
247 {
248 if ($this->bcmath) {
249 return bcdiv($s1, $s2, $scale);
250 } else {
251 return $this->scale((float)$s1 / (float)$s2, $scale);
252 }
253 }
254
255 /**
256 * Rounds a number according to the number of sigfigs it should have,
257 * using arbitrary precision when available.
258 * @param float $n
259 * @param int $sigfigs
260 * @return string
261 */
262 private function round($n, $sigfigs)
263 {
264 $new_log = (int)floor(log(abs($n), 10)); // Number of digits left of decimal - 1
265 $rp = $sigfigs - $new_log - 1; // Number of decimal places needed
266 $neg = $n < 0 ? '-' : ''; // Negative sign
267 if ($this->bcmath) {
268 if ($rp >= 0) {
269 $n = bcadd($n, $neg . '0.' . str_repeat('0', $rp) . '5', $rp + 1);
270 $n = bcdiv($n, '1', $rp);
271 } else {
272 // This algorithm partially depends on the standardized
273 // form of numbers that comes out of bcmath.
274 $n = bcadd($n, $neg . '5' . str_repeat('0', $new_log - $sigfigs), 0);
275 $n = substr($n, 0, $sigfigs + strlen($neg)) . str_repeat('0', $new_log - $sigfigs + 1);
276 }
277 return $n;
278 } else {
279 return $this->scale(round($n, $sigfigs - $new_log - 1), $rp + 1);
280 }
281 }
282
283 /**
284 * Scales a float to $scale digits right of decimal point, like BCMath.
285 * @param float $r
286 * @param int $scale
287 * @return string
288 */
289 private function scale($r, $scale)
290 {
291 if ($scale < 0) {
292 // The f sprintf type doesn't support negative numbers, so we
293 // need to cludge things manually. First get the string.
294 $r = sprintf('%.0f', (float)$r);
295 // Due to floating point precision loss, $r will more than likely
296 // look something like 4652999999999.9234. We grab one more digit
297 // than we need to precise from $r and then use that to round
298 // appropriately.
299 $precise = (string)round(substr($r, 0, strlen($r) + $scale), -1);
300 // Now we return it, truncating the zero that was rounded off.
301 return substr($precise, 0, -1) . str_repeat('0', -$scale + 1);
302 }
303 return sprintf('%.' . $scale . 'f', (float)$r);
304 }
305}
306
307// vim: et sw=4 sts=4