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<?php
namespace kch42\ste;
/**
* Class Calc contains static methods needed by <ste:calc />
*/
class Calc
{
private function __construct()
{
}
/**
* Parse a mathematical expression with the shunting yard algorithm (https://en.wikipedia.org/wiki/Shunting-yard_algorithm)
*
* We could also just eval() the $infix_math code, but this is much cooler :-D (Parser inception)
* @param string $infix_math
* @return array
* @throws RuntimeError
*/
private static function shunting_yard(string $infix_math): array
{
$operators = [
"+" => ["l", 2],
"-" => ["l", 2],
"*" => ["l", 3],
"/" => ["l", 3],
"^" => ["r", 4],
"_" => ["r", 5],
"(" => ["", 0],
")" => ["", 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 = [];
$op_stack = [];
$lastpriority = null;
/* Make - unary, if neccessary */
$tokens = [];
foreach ($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[] = $token;
} elseif ($token == "(") {
$op_stack[] = $token;
} elseif ($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.");
}
} elseif (!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)
&& $priority <= $operators[$op_stack[count($op_stack)-1]][1]
) {
$output_queue[] = array_pop($op_stack);
}
} else {
while (
!empty($op_stack)
&& $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;
}
/**
* @param array $array
* @return array
* @throws RuntimeError
*/
private static function pop2(array &$array): array
{
$rv = [array_pop($array), array_pop($array)];
if (array_search(null, $rv, true) !== false) {
throw new RuntimeError("Not enough numbers on stack. Invalid formula.");
}
return $rv;
}
/**
* @param array $rpn A mathematical expression in reverse polish notation
* @return int|float
* @throws RuntimeError
*/
private static function calc_rpn(array $rpn)
{
$stack = [];
foreach ($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);
}
/**
* Calculate a simple mathematical expression. Supported operators are +, -, *, /, ^.
* You can use ( and ) to group expressions together.
*
* @param string $expr
* @return float|int
* @throws RuntimeError
*/
public static function calc(string $expr)
{
return self::calc_rpn(self::shunting_yard($expr));
}
}
|
