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
308