大整数运算(javascript)(无除法)

var i=0,len=0;
var BigNum=function (s,sign){//+1为正，-1为负
            this.bn=typeof s=="string"?BigNum.big(s.replace('-','')):s;
            this.deal();//处理减法导致的前0
            this.s=(Object.prototype.toString.apply(s) === '[object Array]'?this.show():s).replace('-','');//不含符号
            this.sign=typeof s=="string"?(s.charAt(0)=='-'?-1:1):(sign==-1?-1:1);                  
        };
BigNum.weight=100000000;//好像js的运算精确度知道16位
BigNum.wLen=8;//BigNum.weight.toString().length;
for(i=0,len=BigNum.wLen;i< len;i++)
{
    BigNum["zero"+i]=(1<< i).toString(2).substr(1);//可以定义静态的，i可以到30，即32位，首位为符号位，30个0
}
BigNum.big=function(s){
var len=BigNum.wLen,l=Math.ceil(s.length/len)-1,r=[],i=0;
    for(i=0;i< l;i++){
        r[i]=parseInt(s.substr(-1*(i+1)*len,len),10);
    }
    r[i]=parseInt(s.substr(0,s.length%len||len),10);
    return r;
}
BigNum.prototype.show=function() { 
    var bn=this.bn,l=bn.length-1,i=1,r=[];
    r[0]=""+bn[l];
    while(l--){
        r[++i]=BigNum["zero"+(BigNum.wLen-bn[l].toString().length)]+bn[l];
    }
    return this.sign==1?r.join(""):'-'+r.join("");
};
BigNum.prototype.deal=function() { 
    var i=this.bn.length;
    while(i--){
        if(this.bn[i]!=0||i==0) break;
    }
    this.bn.length=i+1;
};
BigNum.prototype.add=function(b){ 
    var r=[],a=this,an=a.bn,bn=b.bn,la=an.length,lb=bn.length,i=0,len=la>lb?la:lb,m=0,t=0;
    if(a.sign==b.sign){
        for(;i< len;i++){ 
            t=(an[i]||0)+(bn[i]||0)+m;
            r[i]=t%BigNum.weight;
            m=Math.floor(t/BigNum.weight);
        }
        if(m>0){
            r[i]=m;
        }
        return new BigNum(r,a.sign);
    }else{
        var m=this.compare(b);
        if(m==0){
            return new BigNum('0');
        }else{
            if(m<0){
                la=lb,an=bn,bn=a.bn;
            }
            for(i=0;i< la;i++){
                t=an[i]-(bn[i]||0)+t;
                if(t>=0){
                    r[i]=t;
                    t=0;
                }
                else {r[i]=t+BigNum.weight;t=-1;}
            }
            return new BigNum(r,m>0?a.sign:b.sign);
        }
    }
}
BigNum.prototype.multi=function(b){
    var a=this,an=a.bn,la=an.length,bn=b.bn,lb=bn.length,c=[],t=[],r=[],m=0,n=0,i=0,j=0,l=la+lb-1;
    if(lb>la){
        an=bn,la=lb,bn=this.bn,lb=bn.length;
    }
    for(i=0;i< lb;i++){
        c=t[t.length]=[];
        for(j=0;j< la;j++){
            c[j]=an[j]*bn[i];
        }
    }
    for(n=0;n< l||m>0;n++){
        r[n]=m;
        for(i=0;i< lb&&i<=n;i++){
            j=n-i;
            if(j< la){
                r[n]+=t[i][j];
            }
        }
        m=Math.floor(r[n]/BigNum.weight);
        r[n]%=BigNum.weight;
    }
    return new BigNum(r,this.sign*b.sign);
}
BigNum.prototype.compare=function(b){//绝对值的大小比较 return>0 a>b 
    var len=this.s.length,a=len-b.s.length,i=0,t=0;
    if(a!=0){
        return a;
    }
    for(;i< len;i++){
        t=this.s.charCodeAt(i)-b.s.charCodeAt(i);
        if(t!=0){
            return t;
        }
    }
    return 0;
}