function _locale_import_parse_arithmetic

Parses and sanitizes an arithmetic formula into a PHP expression

While parsing, we ensure, that the operators have the right precedence and associativity.

Parameters

$string: A string containing the arithmetic formula.

Return value

The PHP version of the formula.

Related topics

File

includes/locale.inc, line 1286

Code

function _locale_import_parse_arithmetic($string) {
    // Operator precedence table
    $precedence = array(
        "(" => -1,
        ")" => -1,
        "?" => 1,
        ":" => 1,
        "||" => 3,
        "&&" => 4,
        "==" => 5,
        "!=" => 5,
        "<" => 6,
        ">" => 6,
        "<=" => 6,
        ">=" => 6,
        "+" => 7,
        "-" => 7,
        "*" => 8,
        "/" => 8,
        "%" => 8,
    );
    // Right associativity
    $right_associativity = array(
        "?" => 1,
        ":" => 1,
    );
    $tokens = _locale_import_tokenize_formula($string);
    // Parse by converting into infix notation then back into postfix
    // Operator stack - holds math operators and symbols
    $operator_stack = array();
    // Element Stack - holds data to be operated on
    $element_stack = array();
    foreach ($tokens as $token) {
        $current_token = $token;
        // Numbers and the $n variable are simply pushed into $element_stack
        if (is_numeric($token)) {
            $element_stack[] = $current_token;
        }
        elseif ($current_token == "n") {
            $element_stack[] = '$n';
        }
        elseif ($current_token == "(") {
            $operator_stack[] = $current_token;
        }
        elseif ($current_token == ")") {
            $topop = array_pop($operator_stack);
            while (isset($topop) && $topop != "(") {
                $element_stack[] = $topop;
                $topop = array_pop($operator_stack);
            }
        }
        elseif (!empty($precedence[$current_token])) {
            // If it's an operator, then pop from $operator_stack into $element_stack until the
            // precedence in $operator_stack is less than current, then push into $operator_stack
            $topop = array_pop($operator_stack);
            while (isset($topop) && $precedence[$topop] >= $precedence[$current_token] && !($precedence[$topop] == $precedence[$current_token] && !empty($right_associativity[$topop]) && !empty($right_associativity[$current_token]))) {
                $element_stack[] = $topop;
                $topop = array_pop($operator_stack);
            }
            if ($topop) {
                $operator_stack[] = $topop;
                // Return element to top
            }
            $operator_stack[] = $current_token;
            // Parentheses are not needed
        }
        else {
            return FALSE;
        }
    }
    // Flush operator stack
    $topop = array_pop($operator_stack);
    while ($topop != NULL) {
        $element_stack[] = $topop;
        $topop = array_pop($operator_stack);
    }
    // Now extract formula from stack
    $previous_size = count($element_stack) + 1;
    while (count($element_stack) < $previous_size) {
        $previous_size = count($element_stack);
        for ($i = 2; $i < count($element_stack); $i++) {
            $op = $element_stack[$i];
            if (!empty($precedence[$op])) {
                $f = "";
                if ($op == ":") {
                    $f = $element_stack[$i - 2] . "):" . $element_stack[$i - 1] . ")";
                }
                elseif ($op == "?") {
                    $f = "(" . $element_stack[$i - 2] . "?(" . $element_stack[$i - 1];
                }
                else {
                    $f = "(" . $element_stack[$i - 2] . $op . $element_stack[$i - 1] . ")";
                }
                array_splice($element_stack, $i - 2, 3, $f);
                break;
            }
        }
    }
    // If only one element is left, the number of operators is appropriate
    if (count($element_stack) == 1) {
        return $element_stack[0];
    }
    else {
        return FALSE;
    }
}