summaryrefslogtreecommitdiff
path: root/extensions/ParserFunctions/Expr.php
blob: f40158e8815003684727f2ff2f6eda3276b0b2be (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
<?php

if ( !defined( 'MEDIAWIKI' ) ) {
	die( 'This file is a MediaWiki extension, it is not a valid entry point' );
}

// Character classes
define( 'EXPR_WHITE_CLASS', " \t\r\n" );
define( 'EXPR_NUMBER_CLASS', '0123456789.' );

// Token types
define( 'EXPR_WHITE', 1 );
define( 'EXPR_NUMBER', 2 );
define( 'EXPR_NEGATIVE', 3 );
define( 'EXPR_POSITIVE', 4 );
define( 'EXPR_PLUS', 5 );
define( 'EXPR_MINUS', 6 );
define( 'EXPR_TIMES', 7 );
define( 'EXPR_DIVIDE', 8 );
define( 'EXPR_MOD', 9 );
define( 'EXPR_OPEN', 10 );
define( 'EXPR_CLOSE', 11 );
define( 'EXPR_AND', 12 );
define( 'EXPR_OR', 13 );
define( 'EXPR_NOT', 14 );
define( 'EXPR_EQUALITY', 15 );
define( 'EXPR_LESS', 16 );
define( 'EXPR_GREATER', 17 );
define( 'EXPR_LESSEQ', 18 );
define( 'EXPR_GREATEREQ', 19 );
define( 'EXPR_NOTEQ', 20 );
define( 'EXPR_ROUND', 21 );
define( 'EXPR_EXPONENT', 22 );
define( 'EXPR_SINE', 23 );
define( 'EXPR_COSINE', 24 );
define( 'EXPR_TANGENS', 25 );
define( 'EXPR_ARCSINE', 26 );
define( 'EXPR_ARCCOS', 27 );
define( 'EXPR_ARCTAN', 28 );
define( 'EXPR_EXP', 29 );
define( 'EXPR_LN', 30 );
define( 'EXPR_ABS', 31 );
define( 'EXPR_FLOOR', 32 );
define( 'EXPR_TRUNC', 33 );
define( 'EXPR_CEIL', 34 );
define( 'EXPR_POW', 35 );
define( 'EXPR_PI', 36 );
define( 'EXPR_FMOD', 37 );
define( 'EXPR_SQRT' , 38 );

class ExprError extends MWException {
	/**
	 * @param $msg string
	 * @param $parameter string
	 */
	public function __construct( $msg, $parameter = '' ) {
		// Give grep a chance to find the usages:
		// pfunc_expr_stack_exhausted, pfunc_expr_unexpected_number, pfunc_expr_preg_match_failure,
		// pfunc_expr_unrecognised_word, pfunc_expr_unexpected_operator, pfunc_expr_missing_operand,
		// pfunc_expr_unexpected_closing_bracket, pfunc_expr_unrecognised_punctuation,
		// pfunc_expr_unclosed_bracket, pfunc_expr_division_by_zero, pfunc_expr_invalid_argument,
		// pfunc_expr_invalid_argument_ln, pfunc_expr_unknown_error, pfunc_expr_not_a_number
		$msg = wfMessage( "pfunc_expr_$msg", $parameter )->inContentLanguage()->escaped();
		$this->message = '<strong class="error">' . $msg . '</strong>';
	}
}

class ExprParser {
	var $maxStackSize = 100;

	var $precedence = array(
		EXPR_NEGATIVE => 10,
		EXPR_POSITIVE => 10,
		EXPR_EXPONENT => 10,
		EXPR_SINE => 9,
		EXPR_COSINE => 9,
		EXPR_TANGENS => 9,
		EXPR_ARCSINE => 9,
		EXPR_ARCCOS => 9,
		EXPR_ARCTAN => 9,
		EXPR_EXP => 9,
		EXPR_LN => 9,
		EXPR_ABS => 9,
		EXPR_FLOOR => 9,
		EXPR_TRUNC => 9,
		EXPR_CEIL => 9,
		EXPR_NOT => 9,
		EXPR_SQRT => 9,
		EXPR_POW => 8,
		EXPR_TIMES => 7,
		EXPR_DIVIDE => 7,
		EXPR_MOD => 7,
		EXPR_FMOD => 7,
		EXPR_PLUS => 6,
		EXPR_MINUS => 6,
		EXPR_ROUND => 5,
		EXPR_EQUALITY => 4,
		EXPR_LESS => 4,
		EXPR_GREATER => 4,
		EXPR_LESSEQ => 4,
		EXPR_GREATEREQ => 4,
		EXPR_NOTEQ => 4,
		EXPR_AND => 3,
		EXPR_OR => 2,
		EXPR_PI => 0,
		EXPR_OPEN => -1,
		EXPR_CLOSE => -1,
	);

	var $names = array(
		EXPR_NEGATIVE => '-',
		EXPR_POSITIVE => '+',
		EXPR_NOT => 'not',
		EXPR_TIMES => '*',
		EXPR_DIVIDE => '/',
		EXPR_MOD => 'mod',
		EXPR_FMOD => 'fmod',
		EXPR_PLUS => '+',
		EXPR_MINUS => '-',
		EXPR_ROUND => 'round',
		EXPR_EQUALITY => '=',
		EXPR_LESS => '<',
		EXPR_GREATER => '>',
		EXPR_LESSEQ => '<=',
		EXPR_GREATEREQ => '>=',
		EXPR_NOTEQ => '<>',
		EXPR_AND => 'and',
		EXPR_OR => 'or',
		EXPR_EXPONENT => 'e',
		EXPR_SINE => 'sin',
		EXPR_COSINE => 'cos',
		EXPR_TANGENS => 'tan',
		EXPR_ARCSINE => 'asin',
		EXPR_ARCCOS => 'acos',
		EXPR_ARCTAN => 'atan',
		EXPR_LN => 'ln',
		EXPR_EXP => 'exp',
		EXPR_ABS => 'abs',
		EXPR_FLOOR => 'floor',
		EXPR_TRUNC => 'trunc',
		EXPR_CEIL => 'ceil',
		EXPR_POW => '^',
		EXPR_PI => 'pi',
		EXPR_SQRT => 'sqrt',
	);

	var $words = array(
		'mod' => EXPR_MOD,
		'fmod' => EXPR_FMOD,
		'and' => EXPR_AND,
		'or' => EXPR_OR,
		'not' => EXPR_NOT,
		'round' => EXPR_ROUND,
		'div' => EXPR_DIVIDE,
		'e' => EXPR_EXPONENT,
		'sin' => EXPR_SINE,
		'cos' => EXPR_COSINE,
		'tan' => EXPR_TANGENS,
		'asin' => EXPR_ARCSINE,
		'acos' => EXPR_ARCCOS,
		'atan' => EXPR_ARCTAN,
		'exp' => EXPR_EXP,
		'ln' => EXPR_LN,
		'abs' => EXPR_ABS,
		'trunc' => EXPR_TRUNC,
		'floor' => EXPR_FLOOR,
		'ceil' => EXPR_CEIL,
		'pi' => EXPR_PI,
		'sqrt' => EXPR_SQRT,
	);

	/**
	 * Evaluate a mathematical expression
	 *
	 * The algorithm here is based on the infix to RPN algorithm given in
	 * http://montcs.bloomu.edu/~bobmon/Information/RPN/infix2rpn.shtml
	 * It's essentially the same as Dijkstra's shunting yard algorithm.
	 * @param $expr string
	 * @throws ExprError
	 * @return string
	 */
	function doExpression( $expr ) {
		$operands = array();
		$operators = array();

		# Unescape inequality operators
		$expr = strtr( $expr, array( '&lt;' => '<', '&gt;' => '>',
			'&minus;' => '-', '−' => '-' ) );

		$p = 0;
		$end = strlen( $expr );
		$expecting = 'expression';
		$name = '';

		while ( $p < $end ) {
			if ( count( $operands ) > $this->maxStackSize || count( $operators ) > $this->maxStackSize ) {
				throw new ExprError( 'stack_exhausted' );
			}
			$char = $expr[$p];
			$char2 = substr( $expr, $p, 2 );

			// Mega if-elseif-else construct
			// Only binary operators fall through for processing at the bottom, the rest
			// finish their processing and continue

			// First the unlimited length classes

			if ( false !== strpos( EXPR_WHITE_CLASS, $char ) ) {
				// Whitespace
				$p += strspn( $expr, EXPR_WHITE_CLASS, $p );
				continue;
			} elseif ( false !== strpos( EXPR_NUMBER_CLASS, $char ) ) {
				// Number
				if ( $expecting != 'expression' ) {
					throw new ExprError( 'unexpected_number' );
				}

				// Find the rest of it
				$length = strspn( $expr, EXPR_NUMBER_CLASS, $p );
				// Convert it to float, silently removing double decimal points
				$operands[] = floatval( substr( $expr, $p, $length ) );
				$p += $length;
				$expecting = 'operator';
				continue;
			} elseif ( ctype_alpha( $char ) ) {
				// Word
				// Find the rest of it
				$remaining = substr( $expr, $p );
				if ( !preg_match( '/^[A-Za-z]*/', $remaining, $matches ) ) {
					// This should be unreachable
					throw new ExprError( 'preg_match_failure' );
				}
				$word = strtolower( $matches[0] );
				$p += strlen( $word );

				// Interpret the word
				if ( !isset( $this->words[$word] ) ) {
					throw new ExprError( 'unrecognised_word', $word );
				}
				$op = $this->words[$word];
				switch( $op ) {
				// constant
				case EXPR_EXPONENT:
					if ( $expecting != 'expression' ) {
						continue;
					}
					$operands[] = exp( 1 );
					$expecting = 'operator';
					continue 2;
				case EXPR_PI:
					if ( $expecting != 'expression' ) {
						throw new ExprError( 'unexpected_number' );
					}
					$operands[] = pi();
					$expecting = 'operator';
					continue 2;
				// Unary operator
				case EXPR_NOT:
				case EXPR_SINE:
				case EXPR_COSINE:
				case EXPR_TANGENS:
				case EXPR_ARCSINE:
				case EXPR_ARCCOS:
				case EXPR_ARCTAN:
				case EXPR_EXP:
				case EXPR_LN:
				case EXPR_ABS:
				case EXPR_FLOOR:
				case EXPR_TRUNC:
				case EXPR_CEIL:
				case EXPR_SQRT:
					if ( $expecting != 'expression' ) {
						throw new ExprError( 'unexpected_operator', $word );
					}
					$operators[] = $op;
					continue 2;
				}
				// Binary operator, fall through
				$name = $word;
			}

			// Next the two-character operators

			elseif ( $char2 == '<=' ) {
				$name = $char2;
				$op = EXPR_LESSEQ;
				$p += 2;
			} elseif ( $char2 == '>=' ) {
				$name = $char2;
				$op = EXPR_GREATEREQ;
				$p += 2;
			} elseif ( $char2 == '<>' || $char2 == '!=' ) {
				$name = $char2;
				$op = EXPR_NOTEQ;
				$p += 2;
			}

			// Finally the single-character operators

			elseif ( $char == '+' ) {
				++$p;
				if ( $expecting == 'expression' ) {
					// Unary plus
					$operators[] = EXPR_POSITIVE;
					continue;
				} else {
					// Binary plus
					$op = EXPR_PLUS;
				}
			} elseif ( $char == '-' ) {
				++$p;
				if ( $expecting == 'expression' ) {
					// Unary minus
					$operators[] = EXPR_NEGATIVE;
					continue;
				} else {
					// Binary minus
					$op = EXPR_MINUS;
				}
			} elseif ( $char == '*' ) {
				$name = $char;
				$op = EXPR_TIMES;
				++$p;
			} elseif ( $char == '/' ) {
				$name = $char;
				$op = EXPR_DIVIDE;
				++$p;
			} elseif ( $char == '^' ) {
				$name = $char;
				$op = EXPR_POW;
				++$p;
			} elseif ( $char == '(' )  {
				if ( $expecting == 'operator' ) {
					throw new ExprError( 'unexpected_operator', '(' );
				}
				$operators[] = EXPR_OPEN;
				++$p;
				continue;
			} elseif ( $char == ')' ) {
				$lastOp = end( $operators );
				while ( $lastOp && $lastOp != EXPR_OPEN ) {
					$this->doOperation( $lastOp, $operands );
					array_pop( $operators );
					$lastOp = end( $operators );
				}
				if ( $lastOp ) {
					array_pop( $operators );
				} else {
					throw new ExprError( 'unexpected_closing_bracket' );
				}
				$expecting = 'operator';
				++$p;
				continue;
			} elseif ( $char == '=' ) {
				$name = $char;
				$op = EXPR_EQUALITY;
				++$p;
			} elseif ( $char == '<' ) {
				$name = $char;
				$op = EXPR_LESS;
				++$p;
			} elseif ( $char == '>' ) {
				$name = $char;
				$op = EXPR_GREATER;
				++$p;
			} else {
				throw new ExprError( 'unrecognised_punctuation', UtfNormal::cleanUp( $char ) );
			}

			// Binary operator processing
			if ( $expecting == 'expression' ) {
				throw new ExprError( 'unexpected_operator', $name );
			}

			// Shunting yard magic
			$lastOp = end( $operators );
			while ( $lastOp && $this->precedence[$op] <= $this->precedence[$lastOp] ) {
				$this->doOperation( $lastOp, $operands );
				array_pop( $operators );
				$lastOp = end( $operators );
			}
			$operators[] = $op;
			$expecting = 'expression';
		}

		// Finish off the operator array
		while ( $op = array_pop( $operators ) ) {
			if ( $op == EXPR_OPEN ) {
				throw new ExprError( 'unclosed_bracket' );
			}
			$this->doOperation( $op, $operands );
		}

		return implode( "<br />\n", $operands );
	}

	/**
	 * @param $op int
	 * @param $stack array
	 * @throws ExprError
	 */
	function doOperation( $op, &$stack ) {
		switch ( $op ) {
			case EXPR_NEGATIVE:
				if ( count( $stack ) < 1 ) {
					throw new ExprError( 'missing_operand', $this->names[$op] );
				}
				$arg = array_pop( $stack );
				$stack[] = -$arg;
				break;
			case EXPR_POSITIVE:
				if ( count( $stack ) < 1 ) {
					throw new ExprError( 'missing_operand', $this->names[$op] );
				}
				break;
			case EXPR_TIMES:
				if ( count( $stack ) < 2 ) {
					throw new ExprError( 'missing_operand', $this->names[$op] );
				}
				$right = array_pop( $stack );
				$left = array_pop( $stack );
				$stack[] = $left * $right;
					break;
			case EXPR_DIVIDE:
				if ( count( $stack ) < 2 ) {
					throw new ExprError( 'missing_operand', $this->names[$op] );
				}
				$right = array_pop( $stack );
				$left = array_pop( $stack );
				if ( !$right ) {
					throw new ExprError( 'division_by_zero', $this->names[$op] );
				}
				$stack[] = $left / $right;
				break;
			case EXPR_MOD:
				if ( count( $stack ) < 2 ) {
					throw new ExprError( 'missing_operand', $this->names[$op] );
				}
				$right = (int)array_pop( $stack );
				$left = (int)array_pop( $stack );
				if ( !$right ) {
					throw new ExprError( 'division_by_zero', $this->names[$op] );
				}
				$stack[] = $left % $right;
				break;
			case EXPR_FMOD:
				if ( count( $stack ) < 2 ) {
					throw new ExprError( 'missing_operand', $this->names[$op] );
				}
				$right = (double)array_pop( $stack );
				$left = (double)array_pop( $stack );
				if ( !$right ) {
					throw new ExprError( 'division_by_zero', $this->names[$op] );
				}
				$stack[] = fmod( $left, $right );
				break;
			case EXPR_PLUS:
				if ( count( $stack ) < 2 ) {
					throw new ExprError( 'missing_operand', $this->names[$op] );
				}
				$right = array_pop( $stack );
				$left = array_pop( $stack );
				$stack[] = $left + $right;
				break;
			case EXPR_MINUS:
				if ( count( $stack ) < 2 ) {
					throw new ExprError( 'missing_operand', $this->names[$op] );
				}
				$right = array_pop( $stack );
				$left = array_pop( $stack );
				$stack[] = $left - $right;
				break;
			case EXPR_AND:
				if ( count( $stack ) < 2 ) {
					throw new ExprError( 'missing_operand', $this->names[$op] );
				}
				$right = array_pop( $stack );
				$left = array_pop( $stack );
				$stack[] = ( $left && $right ) ? 1 : 0;
				break;
			case EXPR_OR:
				if ( count( $stack ) < 2 ) {
					throw new ExprError( 'missing_operand', $this->names[$op] );
				}
				$right = array_pop( $stack );
				$left = array_pop( $stack );
				$stack[] = ( $left || $right ) ? 1 : 0;
				break;
			case EXPR_EQUALITY:
				if ( count( $stack ) < 2 ) {
					throw new ExprError( 'missing_operand', $this->names[$op] );
				}
				$right = array_pop( $stack );
				$left = array_pop( $stack );
				$stack[] = ( $left == $right ) ? 1 : 0;
				break;
			case EXPR_NOT:
				if ( count( $stack ) < 1 ) {
					throw new ExprError( 'missing_operand', $this->names[$op] );
				}
				$arg = array_pop( $stack );
				$stack[] = ( !$arg ) ? 1 : 0;
				break;
			case EXPR_ROUND:
				if ( count( $stack ) < 2 ) {
					throw new ExprError( 'missing_operand', $this->names[$op] );
				}
				$digits = intval( array_pop( $stack ) );
				$value = array_pop( $stack );
				$stack[] = round( $value, $digits );
				break;
			case EXPR_LESS:
				if ( count( $stack ) < 2 ) {
					throw new ExprError( 'missing_operand', $this->names[$op] );
				}
				$right = array_pop( $stack );
				$left = array_pop( $stack );
				$stack[] = ( $left < $right ) ? 1 : 0;
				break;
			case EXPR_GREATER:
				if ( count( $stack ) < 2 ) {
					throw new ExprError( 'missing_operand', $this->names[$op] );
				}
				$right = array_pop( $stack );
				$left = array_pop( $stack );
				$stack[] = ( $left > $right ) ? 1 : 0;
				break;
			case EXPR_LESSEQ:
				if ( count( $stack ) < 2 ) {
					throw new ExprError( 'missing_operand', $this->names[$op] );
				}
				$right = array_pop( $stack );
				$left = array_pop( $stack );
				$stack[] = ( $left <= $right ) ? 1 : 0;
				break;
			case EXPR_GREATEREQ:
				if ( count( $stack ) < 2 ) {
					throw new ExprError( 'missing_operand', $this->names[$op] );
				}
				$right = array_pop( $stack );
				$left = array_pop( $stack );
				$stack[] = ( $left >= $right ) ? 1 : 0;
				break;
			case EXPR_NOTEQ:
				if ( count( $stack ) < 2 ) {
					throw new ExprError( 'missing_operand', $this->names[$op] );
				}
				$right = array_pop( $stack );
				$left = array_pop( $stack );
				$stack[] = ( $left != $right ) ? 1 : 0;
				break;
			case EXPR_EXPONENT:
				if ( count( $stack ) < 2 ) {
					throw new ExprError( 'missing_operand', $this->names[$op] );
				}
				$right = array_pop( $stack );
				$left = array_pop( $stack );
				$stack[] = $left * pow( 10, $right );
				break;
			case EXPR_SINE:
				if ( count( $stack ) < 1 ) {
					throw new ExprError( 'missing_operand', $this->names[$op] );
				}
				$arg = array_pop( $stack );
				$stack[] = sin( $arg );
				break;
			case EXPR_COSINE:
				if ( count( $stack ) < 1 ) {
					throw new ExprError( 'missing_operand', $this->names[$op] );
				}
				$arg = array_pop( $stack );
				$stack[] = cos( $arg );
				break;
			case EXPR_TANGENS:
				if ( count( $stack ) < 1 ) {
					throw new ExprError( 'missing_operand', $this->names[$op] );
				}
				$arg = array_pop( $stack );
				$stack[] = tan( $arg );
				break;
			case EXPR_ARCSINE:
				if ( count( $stack ) < 1 ) {
					throw new ExprError( 'missing_operand', $this->names[$op] );
				}
				$arg = array_pop( $stack );
				if ( $arg < -1 || $arg > 1 ) {
					throw new ExprError( 'invalid_argument', $this->names[$op] );
				}
				$stack[] = asin( $arg );
				break;
			case EXPR_ARCCOS:
				if ( count( $stack ) < 1 ) {
					throw new ExprError( 'missing_operand', $this->names[$op] );
				}
				$arg = array_pop( $stack );
				if ( $arg < -1 || $arg > 1 ) {
					throw new ExprError( 'invalid_argument', $this->names[$op] );
				}
				$stack[] = acos( $arg );
				break;
			case EXPR_ARCTAN:
				if ( count( $stack ) < 1 ) {
					throw new ExprError( 'missing_operand', $this->names[$op] );
				}
				$arg = array_pop( $stack );
				$stack[] = atan( $arg );
				break;
			case EXPR_EXP:
				if ( count( $stack ) < 1 ) {
					throw new ExprError( 'missing_operand', $this->names[$op] );
				}
				$arg = array_pop( $stack );
				$stack[] = exp( $arg );
				break;
			case EXPR_LN:
				if ( count( $stack ) < 1 ) {
					throw new ExprError( 'missing_operand', $this->names[$op] );
				}
				$arg = array_pop( $stack );
				if ( $arg <= 0 ) {
					throw new ExprError( 'invalid_argument_ln', $this->names[$op] );
				}
				$stack[] = log( $arg );
				break;
			case EXPR_ABS:
				if ( count( $stack ) < 1 ) {
					throw new ExprError( 'missing_operand', $this->names[$op] );
				}
				$arg = array_pop( $stack );
				$stack[] = abs( $arg );
				break;
			case EXPR_FLOOR:
				if ( count( $stack ) < 1 ) {
					throw new ExprError( 'missing_operand', $this->names[$op] );
				}
				$arg = array_pop( $stack );
				$stack[] = floor( $arg );
				break;
			case EXPR_TRUNC:
				if ( count( $stack ) < 1 ) {
					throw new ExprError( 'missing_operand', $this->names[$op] );
				}
				$arg = array_pop( $stack );
				$stack[] = (int)$arg;
				break;
			case EXPR_CEIL:
				if ( count( $stack ) < 1 ) {
					throw new ExprError( 'missing_operand', $this->names[$op] );
				}
				$arg = array_pop( $stack );
				$stack[] = ceil( $arg );
				break;
			case EXPR_POW:
				if ( count( $stack ) < 2 ) {
					throw new ExprError( 'missing_operand', $this->names[$op] );
				}
				$right = array_pop( $stack );
				$left = array_pop( $stack );
				if ( false === ( $stack[] = pow( $left, $right ) ) ) {
					throw new ExprError( 'division_by_zero', $this->names[$op] );
				}
				break;
			case EXPR_SQRT:
				if ( count( $stack ) < 1 ) {
					throw new ExprError( 'missing_operand', $this->names[$op] );
				}
				$arg = array_pop( $stack );
				$result = sqrt( $arg );
				if ( is_nan( $result ) ) {
					throw new ExprError( 'not_a_number', $this->names[$op] );
				}
				$stack[] = $result;
				break;
			default:
				// Should be impossible to reach here.
				throw new ExprError( 'unknown_error' );
		}
	}
}