var last_result='';
       var saved_result='';
       var last_input='';
       var last_printed=''
       var modifying_history=false;
       var history_index=1;
       
       // add by bo
       var checkDot = 1;
       var checkZero = 1;
 
       var regex_HexDigit='(?:[0-9a-fA-F])';
       var regex_Digit='(?:[0-9])';
       var regex_OctalDigit='(?:[0-7])';
       var regex_NonZeroDigit='(?:[1-9])';
       var regex_Sign='(?:[\+]|[\-])';
       var regex_DecimalNum='(?:(?:[0]|'+regex_NonZeroDigit+regex_Digit+'*))';
       var regex_OctalNum='(?:[0]'+regex_OctalDigit+'*)';
       var regex_HexNum='(?:[0](?:[x]|[X])'+regex_HexDigit+'+)';
       var regex_SignedInt='(?:'+regex_Sign+'?'+regex_Digit+'+)';
       var regex_Expo='(?:[e]|[E])';
       var regex_ExponentPart='(?:'+regex_Expo+regex_SignedInt+')';
       var regex_Float1='(?:'+regex_Digit+'+[\.]'+regex_Digit+'*'+regex_ExponentPart+'?)';
       var regex_Float2='(?:[\.]'+regex_Digit+'+'+regex_ExponentPart+'?)';
       var regex_Float3='(?:'+regex_Digit+'+'+regex_ExponentPart+')';
       var regex_Float4='(?:'+regex_Digit+'+)';
       var regex_Float='(?:'+regex_Float1+'|'+regex_Float2+'|'+regex_Float3+'|'+regex_Float4+')';
       var regex_ZeroFloat1='(?:[0]+[\.][0]*'+regex_ExponentPart+'?)';
       var regex_ZeroFloat2='(?:[\.][0]+'+regex_ExponentPart+'?)';
       var regex_ZeroFloat3='(?:[0]+'+regex_ExponentPart+')';
       var regex_ZeroFloat4='(?:[0]+)';
       var regex_ZeroFloat='(?:'+regex_ZeroFloat1+'|'+regex_ZeroFloat2+'|'+regex_ZeroFloat3+'|'+regex_ZeroFloat4+')';
       var regex_Space='(?:[\n\ \t])';
       var regex_Operands='(?:[\(\)\+\-\/\*\|\&\,\~\^]|\<\<|\>\>|\>\>\>|\%)'
       var regex_MathStuff='(?:E|LN10|LN2|LOG10E|LOG2E|PI|SQRT1_2|SQRT2|abs|acos|asin|atan2|atan|ceil|cos|exp|floor|log|max|min|pow|random|round|sin|sqrt|tan)'
       var regex_Functions='(?:(?:Math[\.]'+regex_MathStuff+')|'+regex_MathStuff+')';
       var regex_allowable=new RegExp(
       	regex_HexNum+'|'+regex_OctalNum+'|'+regex_Float+'|'+regex_DecimalNum+'|'+
       	regex_ZeroFloat+'|'+regex_Space+'|'+regex_Operands+'|'+regex_Functions+'|ans','g'
       );
 
       var E=Math.E;
       var LN10=Math.LN10;
       var LN2=Math.LN2;
       var LOG10E=Math.LOG10E;
       var LOG2E=Math.LOG2E;
       var PI=Math.PI;
       var SQRT1_2=Math.SQRT1_2;
       var SQRT2=Math.SQRT2;
       function abs(x){return Math.abs(x);}
       function acos(x){return Math.acos(x);}
       function asin(x){return Math.asin(x);}
       function atan(x){return Math.atan(x);}
       function atan2(x){return Math.atan2(x);}
       function ceil(x){return Math.ceil(x);}
       function cos(x){return Math.cos(x);}
       function exp(x){return Math.exp(x);}
       function floor(x){return Math.floor(x);}
       function log(x){return Math.log(x);}
       function max(x,y){return Math.max(x,y);}
       function min(x,y){return Math.min(x,y);}
       function pow(x,y){return Math.pow(x,y);}
       function random(){return Math.random();}
       function round(x){return Math.round(x);}
       function sin(x){return Math.sin(x);}
       function sqrt(x){return Math.sqrt(x);}
       function tan(x){return Math.tan(x);}
 
       function replace_binary(s){
       	var r=new RegExp("^((?:[a]|[^a])*)0[bB]([01]{1,32})((?:[a]|[^a])*)$");
       	while(r.exec(s)){
       		s=RegExp.$1+" "+from_bin(RegExp.$2)+" "+RegExp.$3;
       	}
       	return s;
       }
 
       function replace_ans(s){
       	var r=new RegExp("^((?:[a]|[^a])*)ans((?:[a]|[^a])*)$");
       	while(r.exec(s)){
       		s=RegExp.$1+" "+saved_result+" "+RegExp.$2;
       	}
       	return s;
       }
 
       function do_calculation(){
       	var current_calc=document.calculator.line.value; // equation
       	var mod_calc=replace_ans(current_calc);
       	mod_calc=replace_binary(mod_calc);
       	if(mod_calc!=last_printed&&mod_calc!=last_input&&!modifying_history){
       		var not_allowed=mod_calc.split(regex_allowable);
       		var num_badTokens=0;
       		for(var k=0;k<not_allowed.length;k++){
       			if(not_allowed[k].length!=0){
       				num_badTokens++;
       			}
       		}
       		if(num_badTokens==0){
       			try{
       				var calc_result=''+eval(mod_calc);
       				if(calc_result!=undefined){
       					last_result=calc_result;
       					saved_result=calc_result;
       					last_input='';
       					display_result();
       					add_toHistory(current_calc);
       					save_calc();
       				}
       			}catch(ex){
       				alert('Error type: '+ex.name+'\n'+'Error message: '+ex.message);
       				last_input=document.calculator.line.value;
       			}
       		}else{
       			alert(num_badTokens+' unknown tokens:\n'+not_allowed);
       			last_input=document.calculator.line.value;
       		}
       		document.calculator.line.focus();
       	}
       }
       function line_change(){
       	if(last_printed!=document.calculator.line.value){
       		last_result='';
       	}
       }
       function display_result(){
       	if(last_result!=''){
       		var should_display=document.calculator.display.selectedIndex;
       		var int_val=parseInt(last_result);
       		var float_val=parseFloat(last_result);
       		var to_print='';
       		if(''+float_val!='NaN'&&should_display==1){
       			to_print=to_sci(last_result,false);
       		}else if(''+float_val!='NaN'&&should_display==2){
       			to_print=to_sci(last_result,true);
       		}else if(''+int_val!='NaN'&&should_display==3){
       			to_print=to_hex(int_val);
       		}else if(''+int_val!='NaN'&&should_display==4){
       			to_print=to_octal(int_val);
       		}else if(''+int_val!='NaN'&&should_display==5){
       			to_print=to_bin(int_val);
       		}else{
			var clast_result = last_result.split(".");
			if(clast_result[1]!="" && clast_result[1]!= null)
			{
				if(clast_result[1].length > 4)
				{
					float_val = float_val.toFixed(4);
				}
				if(clast_result[0].length > 6){
					to_print = float_val.toExponential(3);
				}
				else{
					to_print = float_val;
				}
			}else{
				if(clast_result[0].length > 6){
					to_print = float_val.toExponential(3);
				}
				else{
					to_print = float_val;
				}
			}
       		}
       		last_printed=to_print;
       		document.calculator.line.value=to_print;
       		history_index=1;
       		document.calculator.line.style.backgroundColor='#fff';
       	}else{
       		document.calculator.line.style.backgroundColor='#fff';
       	}
       }
       function to_sci(s,eng){
       	var the_exp=0;
       	var is_negative=false;
       	if(s.length>0&&s.charAt(0)=='-'){
       		is_negative=true;
       		s=s.substring(1,s.length);
       	}
       	var regex_splitter=s.split(new RegExp('[eE]'));
       	if(regex_splitter.length>1){
       		the_exp=parseInt(regex_splitter[1]);
       		s=regex_splitter[0];
       	}
       	regex_splitter=s.split(/[\.]/);
       	if(regex_splitter.length>1){
       		s=regex_splitter[0]+regex_splitter[1];
       		the_exp+=regex_splitter[0].length-1;
       	}else{
       		the_exp+=s.length-1;
       	}
       	var leading_zeros=0;
       	for(leading_zeros=0;leading_zeros<s.length&&s.charAt(leading_zeros)=='0';leading_zeros++){
       		the_exp=the_exp-1;
       	}
       	s=s.substring(leading_zeros,s.length);
       	var move_dec;
       	if(eng){
       		if(the_exp>=0){
       			move_dec=(the_exp%3)+1;
       		}else{
       			move_dec=4-((-the_exp)%3);
       			if(move_dec==4){
       				move_dec=1;
       			}
       		}
       		the_exp-=(move_dec-1);
       	}else{
       		move_dec=1;
       	}
       	var trailing_zeros='';
       	for(var i=s.length;i<move_dec;i++){
       		trailing_zeros+='0';
       	}
       	return(
       		(is_negative?'-':'')+
       		((s.length==0)?'0':s.substring(0,move_dec))+
       		((s.length<=move_dec)?trailing_zeros:('.'+s.substring(move_dec,s.length)))+
       		((s.length==0||the_exp==0)?'':('e'+the_exp))
       	);
       }
       var digit_array=new Array('0','1','2','3','4','5','6','7','8','9','a','b','c','d','e','f');
       function to_hex(n){
       	var hex_result=''
       	var the_start=true;
       	for(var i=32;i>0;){
       		i-=4;
       		var one_digit=(n>>i)&0xf;
       		if(!the_start||one_digit!=0){
       			the_start=false;
       			hex_result+=digit_array[one_digit];
       		}
       	}
       	return '0x'+(hex_result==''?'0':hex_result);
       }
 
       function to_octal(n){
       	var oct_result=''
       	var the_start=true;
       	for(var i=33;i>0;){
       		i-=3;
       		var one_digit=(n>>i)&0x7;
       		if(!the_start||one_digit!=0){
       			the_start=false;
       			oct_result+=digit_array[one_digit];
       		}
       	}
       	return '0'+(oct_result==''?'0':oct_result);
       }
 
       function to_bin(n){
       	var bin_result=''
       	var the_start=true;
       	for(var i=32;i>0;){
       		i-=1;
       		var one_digit=(n>>i)&0x1;
       		if(!the_start||one_digit!=0){
       			the_start=false;
       			bin_result+=digit_array[one_digit];
       		}
       	}
       	return '0b'+(bin_result==''?'0':bin_result);
       }
 
       function from_bin(s){
       	var bin_result=0;
       	var the_place=0;
       	var i=s.length-1;
       	while(i>=0&&the_place<32){
       		if(s.charAt(i)=='1'){
       			bin_result|=1<<the_place;
       		}
       		the_place++;
       		i-=1;
       	}
       	return bin_result;
       }
 
       function set_calc(s){
       	if(!modifying_history&&s!=''){
       		last_result='';
       		last_input=s;
       		document.calculator.line.value=s;
       		document.calculator.line.focus();
       		last_input='';
       		last_printed='';
       		history_index=1;
       		document.calculator.line.style.backgroundColor='#fff';
       		document.calculator.line.focus();
       	}
       }
       // add by bo
       function IsNumeric(sText){	
		var number ="0123456789";
		var isNumber = true;
		var char;
		for(i=0; i<sText.length ;i++){
			char =sText.charAt(i)
			if(number.indexOf(char) == -1){
				isNumber = false;
			}			
		}
		return isNumber;
       }
        //==============
       function append_calc(s,replaceLast){
       
      //alert("last Input: "+document.calculator.line.value.charAt(document.calculator.line.value.length-1));
       //if(document.calculator.line.value == '0' && s == '0'){ checkZero=0;}else{checkZero =1;} 
	if(document.calculator.line.value == '0'  || document.calculator.line.value ==' '){
		if(s == '0'){
			checkZero=0;
			last_input='0';
			last_result='';
			document.calculator.line.value = '0';
			document.calculator.line.focus();
		}else{
			if(IsNumeric(s)){	
				document.calculator.line.value ='';
			}
			checkZero =1;				
		}
	}
        if(document.calculator.line.value.length < 12){
		if(checkZero){
			if(checkDot || s!="."){
			       	if(!modifying_history&&s!=''){
			       		last_result='';
			       		var new_contents
			       		if(replaceLast==0&&document.calculator.line.value==last_printed){
			       			new_contents=s;
			       		}else if(replaceLast==1&&document.calculator.line.value==last_printed){
			       			new_contents='ans '+s;
			       		}else{
			       			new_contents=document.calculator.line.value+s;
			       		}
			       		last_input=new_contents;
			       		document.calculator.line.value=new_contents;
			       		document.calculator.line.focus();
			       		last_input='';
			       		last_printed='';
			       		history_index=1;
			       		document.calculator.line.style.backgroundColor='#fff';
			       		document.calculator.line.focus();
			       	}
			}
		}
		if(s =="."){checkDot = 0;}		
	}else{
		alert("You cannot insert more digits.");
	}
       }
       function clear_calc(){
       	document.calculator.line.value='';
       	history_index=1;
	checkDot=1;
       	document.calculator.line.style.backgroundColor='#fff';
       	document.calculator.line.focus();
       }
       function add_toHistory(s){
       	modifying_history=true;
       	var is_found=false;
       	var the_last=s;
       	var next_history;
       	var history_elements=document.calculator.history.options;
       	for(var i=1;i<history_elements.length&&!is_found;i++){
       		next_history=history_elements[i].text;
       		history_elements[i].text=the_last;
       		if(next_history==s){
       			is_found=true;
       		}
       		the_last=next_history;
       	}
       	document.calculator.history.selectedIndex=0;
       	modifying_history=false;
       }
       function load_calc(){
       	modifying_history=true;
       	var history_elements=document.calculator.history.options;
       	var calc_cookie=get_cookie('calculatorState');
       	if(calc_cookie!=null&&calc_cookie.length>1){
       		var history_part=calc_cookie.substring(1,calc_cookie.length);
       		if(history_part!=null){
       			var history_split=history_part.split('\n');
       			for(var i=1;i<history_elements.length&&i<history_split.length+1;i++){
       				history_elements[i].text=history_split[i-1];
       			}
       		}
       		document.calculator.display.selectedIndex=parseInt(calc_cookie.charAt(0));
       	}
       	modifying_history=false;
       }
       function save_calc(){
       	var history_elements=document.calculator.history.options;
       	var calc_cookie=document.calculator.display.selectedIndex;
       	for(var i=1;i<history_elements.length;i++){
       		calc_cookie+=history_elements[i].text+'\n';
       	}
       	var expires_date=new Date();
       	// cookie expires in one year
       	expires_date.setTime(expires_date.getTime()+365*24*60*60*1000);
       	document.calc_cookie=(
       		'calculatorState'+'='+
       		escape(calc_cookie)+
       		';expires='+expires_date.toGMTString()
       	);
       }
       function get_cookie(name){
       	var cookie_prefix=name+"=";
       	var cookie_begin=document.cookie.indexOf(";"+cookie_prefix);
       	if(cookie_begin==-1){
       		cookie_begin=document.cookie.indexOf(cookie_prefix);
       		if(cookie_begin!=0)return null;
       	}else{
       		cookie_begin+=2;
       	}
       	var cookie_end=document.cookie.indexOf(";",cookie_begin);
       	if(cookie_end==-1)cookie_end=document.cookie.length;
       	return unescape(document.cookie.substring(cookie_begin+cookie_prefix.length,cookie_end));
       }
       function display_nextHistory(){
       	var history_elements=document.calculator.history.options;
       	var next_history="";
       	if(history_index>=history_elements.length||history_elements[history_index].text==""){
       		history_index=1;
       	}
       	if(history_elements[history_index].text!=""){
       		var temp_history=history_index;
       		set_calc(history_elements[history_index].text);
       		history_index=temp_history;
       		document.calculator.history.selectedIndex=history_index;
       		history_index++;
       	}
       	document.calculator.line.focus();
       }
       function next_display_method(){
       	var d=document.calculator.display;
       	var s=d.selectedIndex;
       	s++;
       	if(s>=d.options.length)s=0;
       	display_method(s)
       }
       function display_method(index){
       	document.calculator.display.selectedIndex=index;
       	display_result();
       	save_calc();
       	document.calculator.line.focus();
       }