Java BigInteger Implementation

The bottom of the BigInteger is implemented with int[].

Before looking at the data structure, always thought that BigInteger is implemented with a linked list. But later found that it was only a practice to increase the difficulty of the use.

It was later found that the string implementation is much faster than the linked list. I thought it was implemented with string.

But a check, only found that the original use int[] to achieve.

Yes, with int[] it saves the trouble of character-to-number!

The addition and multiplication algorithm implemented by string is given below. The idea is the same as our hand.

 public string Mulonedigit (string num1, char digit, int. level) {StringBuilder SB = new StringBuilder ();        int carry = 0;  for (int i = Num1.length ()-1; I >= 0 | | carry! = 0;            i--) {int tmp = i < 0? 0:num1.charat (i)-' 0 ';            Sb.insert (0, (TMP * (digit-' 0 ') + carry)% 10);        carry = (TMP * (digit-' 0 ') + carry)/10;            } while (Level > 0) {sb.append (0);        level--;    } return sb.tostring ();  }/** * Use: To circumvent the two loops, and note the highest bit in the case * @param num1 * @param num2 * @return */public string Add (string        NUM1, String num2) {StringBuilder sb = new StringBuilder ();        int carry = 0;  for (int i = Num1.length ()-1, J = num2.length ()-1; I >= 0 | | j>=0 | | Carry! = 0;            I--, j--) {int a = i < 0? 0:num1.charat (i)-' 0 '; int B = J < 0?            0:num2.charat (j)-' 0 ';            Sb.insert (0, (a+b+carry)% 10); Carry = (A+b+carRY)/10;    } return sb.tostring ();        public string Multiply (string num1, String num2) {string small, large;            if (Num1.length () > Num2.length ()) {large = NUM1;        small = num2;            }else {large = num2;        small = NUM1;        } list<string> stringlist = new arraylist<> ();        int level = 0;         for (int i = Small.length ()-1; I >= 0; i--) {Stringlist.add (Mulonedigit (large, Small.charat (i), level++));        The String result = "0";        for (String str:stringlist) {result = Add (str, result);        } if (Result.charat (0) = = ' 0 ') {result = "0";    } return result; }

　　

Java BigInteger Implementation