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<?php
namespace kch42\ste;
/* Class Calc contains static methods needed by <ste:calc /> */
class Calc {
private function __construct() {}
/* We could also just eval() the $infix_math code, but this is much cooler :-D (Parser inception) */
public static function shunting_yard($infix_math) {
$operators = array(
"+" => array("l", 2),
"-" => array("l", 2),
"*" => array("l", 3),
"/" => array("l", 3),
"^" => array("r", 4),
"_" => array("r", 5),
"(" => array("", 0),
")" => array("", 0)
);
preg_match_all("/\s*(?:(?:[+\\-\\*\\/\\^\\(\\)])|(\\d*[\\.]?\\d*))\\s*/s", $infix_math, $tokens, PREG_PATTERN_ORDER);
$tokens_raw = array_filter(array_map('trim', $tokens[0]), function($x) { return ($x === "0") || (!empty($x)); });
$output_queue = array();
$op_stack = array();
$lastpriority = NULL;
/* Make - unary, if neccessary */
$tokens = array();
foreach($tokens_raw as $token) {
$priority = isset($operators[$token]) ? $operators[$token][1] : -1;
if(($token == "-") && (($lastpriority === NULL) || ($lastpriority >= 0))) {
$priority = $operators["_"][1];
$tokens[] = "_";
} else {
$tokens[] = $token;
}
$lastpriority = $priority;
}
while(!empty($tokens)) {
$token = array_shift($tokens);
if(is_numeric($token)) {
$output_queue[] = $token;
} else if($token == "(") {
$op_stack[] = $token;
} else if($token == ")") {
$lbr_found = false;
while(!empty($op_stack)) {
$op = array_pop($op_stack);
if($op == "(") {
$lbr_found = true;
break;
}
$output_queue[] = $op;
}
if(!$lbr_found) {
throw new RuntimeError("Bracket mismatch.");
}
} else if(!isset($operators[$token])) {
throw new RuntimeError("Invalid token ($token): Not a number, bracket or operator. Stop.");
} else {
$priority = $operators[$token][1];
if($operators[$token][0] == "l") {
while((!empty($op_stack)) and ($priority <= $operators[$op_stack[count($op_stack)-1]][1])) {
$output_queue[] = array_pop($op_stack);
}
} else {
while((!empty($op_stack)) and ($priority < $operators[$op_stack[count($op_stack)-1]][1])) {
$output_queue[] = array_pop($op_stack);
}
}
$op_stack[] = $token;
}
}
while(!empty($op_stack)) {
$op = array_pop($op_stack);
if($op == "(") {
throw new RuntimeError("Bracket mismatch...");
}
$output_queue[] = $op;
}
return $output_queue;
}
public static function pop2(&$array) {
$rv = array(array_pop($array), array_pop($array));
if(array_search(NULL, $rv, true) !== false) {
throw new RuntimeError("Not enough numbers on stack. Invalid formula.");
}
return $rv;
}
public static function calc_rpn($rpn) {
$stack = array();
foreach($rpn as $token) {
switch($token) {
case "+":
list($b, $a) = self::pop2($stack);
$stack[] = $a + $b;
break;
case "-":
list($b, $a) = self::pop2($stack);
$stack[] = $a - $b;
break;
case "*":
list($b, $a) = self::pop2($stack);
$stack[] = $a * $b;
break;
case "/":
list($b, $a) = self::pop2($stack);
$stack[] = $a / $b;
break;
case "^":
list($b, $a) = self::pop2($stack);
$stack[] = pow($a, $b);
break;
case "_":
$a = array_pop($stack);
if($a === NULL) {
throw new RuntimeError("Not enough numbers on stack. Invalid formula.");
}
$stack[] = -$a;
break;
default:
$stack[] = $token;
break;
}
}
return array_pop($stack);
}
public static function calc($expr) {
return self::calc_rpn(self::shunting_yard($expr));
}
}
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