FactorialLookup.js

"use asm";

(function(){

    function multiplyStrings(a,b){
        var result = [];
	var dummy = [];


        for(var i=0; i < b.length; i++) {
   	    if( i ) dummy.push(0);
            var dummy2 = multiplyWithOneDigit(a,b[i], dummy.slice());
            result = addToStringumbers(result,dummy2);
        }
        return result;
    }

    function multiplyWithOneDigit(a,b,base){
        var result      = base;
        var carry       = 0;
        for(var i=0; i < a.length; i++) {
	   var op = a[i]*b+carry;
           carry = (op/100000)|0;
	   result.push(op%100000); 
        }
	if( carry ) result.push(carry);
        return result;
    }


    function addToStringumbers(a,b){
        if(a.length == 0)
            return b;

        var carry = 0;
        var result = [];

        for(var i=0; i < b.length; i++){
	   if( i >= a.length )
 	      var op = b[i]+carry;
	   else
 	      var op = a[i]+b[i]+carry;
   	   carry = (op/100000)|0;
           result.push( op%100000 );
        }
        if(carry) result.push( carry );

        return result;
    }

    function intToArray(i) {
	var tmp = i.toString().split('').reverse().map( (a)=>parseInt(a) );
	var tmp2 = [];
	var parts = (((tmp.length+4)/5)|0) - 1; 
	var last = tmp.length % 5;
	for( var n = 0; n < parts; n++ ) {
		tmp2.push( tmp[n*5+0] * 1 + tmp[n*5+1] * 10 + tmp[n*5+2] * 100 + tmp[n*5+3] * 1000 + tmp[n*5+4] * 10000 );  
	}
		if( last == 0 )
			tmp2.push( tmp[n*5+0] * 1 + tmp[n*5+1] * 10 + tmp[n*5+2] * 100 + tmp[n*5+3] * 1000 + tmp[n*5+4] * 10000 );  
		else if( last == 4 )
			tmp2.push( tmp[n*5+0] * 1 + tmp[n*5+1] * 10 + tmp[n*5+2] * 100 + tmp[n*5+3] * 1000 );  
		else if( last == 3 )
			tmp2.push( tmp[n*5+0] * 1 + tmp[n*5+1] * 10 + tmp[n*5+2] * 100 );  
		else if( last == 2 )
			tmp2.push( tmp[n*5+0] * 1 + tmp[n*5+1] * 10 );  
		else 
			tmp2.push( tmp[n*5+0] * 1 );  

       return tmp2;
    }

    function factorial(x){
        var result = [1];
        for(var i=2; i<=x; i++){
            result = multiplyStrings(result, intToArray(i));
        }
	
        var tmp = result.reverse();
	var tmp2 = tmp.map( (n,i)=>{ 
            var s = n.toString(10);
            if( i ) for( var n = s.length; n < 5; n++ ) s = "0" + s; 
            return s } );
	return tmp2.join("");
	
    }

var now = Date.now();
    console.log(factorial(process.argv[2]));
console.log( "del:", Date.now() - now );

}());