我就给一个PHP逆波兰表达式的算法吧---工资计算专用

有个网友写信给我谈到关于PHP计算工资问题。我以前一篇文章中谈到过一种计算工资的方法，不过是偷巧，利用现有的表达式的工具，现在既然有人想要，我就给出一个逆波兰的算法。

 我们的目标是实现如下的计算公式：

假设有一个计算公式如下：      $expression = "(F1*F12+10.34)";

其中的变量值如下：

$expression_value = Array('F1'=>10,
                                                 'F12'=>20);

我们希望用PHP构建一个类来计算出这个表达式的值。这种应用主要用于web工资管理中，用户可以自定义其工资相公式的情况

      $rpn = new Math_Rpn();
      $rpn->setExpressionValue($expression_value);
     
      echo $rpn->calculate($expression,'deg',false);  // 即为相应的值

解析逆波兰表达式的方法，编译原理中有，就是先把表达式分解成符号数组，然后求逆波兰式，最后根据逆波兰式得到其结果。

我分别把三个函数贴在下面，其实本质我就是对Pear的RPN函数进行了Hack.

    function _stringToArray () {
        $temp_operator = null;
        $temp_value = null;

        $this->_input = str_replace(" ","",$this->_input);

        for($i = 0; $i < strlen($this->_input); $i++) {
            if ($this->_input[$i] == ' ') {
                if ($temp_operator != null) {
                    array_push($this->_input_array, $temp_operator);
                    $temp_operator = null;
                }
                if ($temp_value != null) {
                    array_push($this->_input_array, $temp_value);
                    $temp_value = null;
                }
            } elseif (($temp_value == null) && $temp_operator != ')' && (!array_key_exists($temp_operator,$this->_operation) || !array_key_exists(2,$this->_operation[$temp_operator]) || $this->_operation[$temp_operator][2]>0) && ($this->_input[$i] == '-')) {
                if ($temp_operator != null) {
                    array_push($this->_input_array, $temp_operator);
                    $temp_operator = null;
                }

                array_push($this->_input_array, '-1');
                array_push($this->_input_array, '*');
            //} elseif ((is_numeric($this->_input[$i])) || ($this->_input[$i] == '.')) {
            } elseif ((is_numeric($this->_input[$i])) || ($this->_input[$i] == '.') || ($this->_input[$i] == 'F')) {
                if ($temp_operator != null) {
                    array_push($this->_input_array, $temp_operator);
                    $temp_operator = null;
                }

                $temp_value .= $this->_input[$i];
            } else {
                if ($this->_keyExists($temp_operator, $this->_operation, 1)) {
                    array_push($this->_input_array, $temp_operator);
                    $temp_operator = null;
                }

                if ($temp_value != null) {
                    array_push($this->_input_array, $temp_value);
                    $temp_value = null;
                }

                $temp_operator .= $this->_input[$i];
            }
        }

        if ($temp_operator != null && $temp_operator != ' ') {
            array_push($this->_input_array, $temp_operator);
        } elseif($temp_value != null && $temp_value != ' ') {
            array_push($this->_input_array, $temp_value);
        }

       // $this->_testInput();
print_r($this->_expression_value);
        print_r($this->_input_array);
        return $this->_input_array;
    }

    function _arrayToRpn() {

        if ($this->_error <> null) {
            $this->_output = array();
            return $this->_output;
        }

        for($i = 0; $i < count($this->_input_array); $i++) {

            $temp = $this->_input_array[$i];
           
            if (is_numeric($temp)) {
                $this->_outputAdd($temp);
            } else if($this->_keyExists($temp, $this->_expression_value, 0)) {
               $this->_outputAdd($this->_expression_value[$temp]);
            } else {
                if ($temp == ')') {
                    while(!$this->_stackEmpty() && ($this->_stackPriority() >= 1)) {
                        $this->_outputAdd($this->_stackDelete());
                    }
                    if (!$this->_stackEmpty()) {
                        $this->_stackDelete();
                    }

                } elseif ($temp=='(') {
                    $this->_stackAdd($temp);
                } elseif (($this->_stackEmpty()) || (($this->_priority($temp) > $this->_stackPriority()))) {
                   $this-> _stackAdd($temp);
                } else {
                    while(!$this->_stackEmpty() && ($this->_priority($temp) <= $this->_stackPriority())) {
                        $this->_outputAdd($this->_stackDelete());
                    }
                    $this->_stackAdd($temp);
                }

            }

        }

        while(!$this->_stackEmpty()) {
            $this->_outputAdd($this->_stackDelete());
        }

        return $this->_output;
    }

    function _rpnToValue() {

        $time1 = $this->_getMicroTime();

        if ($this->_error <> null) {
            $this->_value = null;
            return $this->_value;
        }

        $this->_value = 0;
        $temp = $this->_output;

        do {
            $pos = $this->_nextOperator($temp);

            if ($pos == -1) {
                $this->_error = $this->_raiseError('Syntax error');
                $this->_value = null;
                return $this->_value;
            }

            $operator = $this->_operation[$temp[$pos]];
            $arg = $operator[2];
            $function = $operator[3];

            if (($arg==2) && (!isset($temp[$pos-1]) || !is_numeric($temp[$pos-1]) || !isset($temp[$pos-2]) || !is_numeric($temp[$pos-2]))) {
                $this->_error = $this->_raiseError('Syntax error');
                $this->_value = null;
                return $this->_value;
            } elseif (($arg==1) && (!isset($temp[$pos-1]) || !is_numeric($temp[$pos-1]))) {
                $this->_error = $this->_raiseError('Syntax error');
                $this->_value = null;
                return $this->_value;
            }

            if(is_array($function)) {

                if($arg==2) $arg_array = array($temp[$pos-2],$temp[$pos-1]);
                elseif($arg==1) $arg_array = array($temp[$pos-1]);
                else $arg_array = array();

                if($function['type'] == 'userFunction') {
                    $this->_value = call_user_func_array($function['function'], $arg_array);
                } else {
                    $function_array = array(&$function['class'], $function['method']);
                    $this->_value = call_user_func_array($function_array, $arg_array);
                }
            } else {
                $this->_value = $this->$function($temp, $pos);
            }

            if ($this->_isNan($this->_value)) {
                $this->_error = $this->_raiseError('NAN value');
                $this->_value = null;
                return $this->_value;
            } elseif ($this->_isInfinite($this->_value)) {
                $this->_error = $this->_raiseError('Infinite value');
                $this->_value = null;
                return $this->_value;
            } elseif (is_null($this->_value)) {
                return $this->_value;
            }

            $temp = $this->_refresh($temp, $pos, $arg, $this->_value);
        } while(count($temp) > 1);

        $this->_value = $temp[0];

        $time2 = $this->_getMicroTime();

        $this->_timer = $time2 - $time1;

        return $this->_value;
    }