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