The source code and analysis of BigInteger large number home law

2. Public BigInteger (String val, int radix) {
6. int cursor = 0, numdigits;
8. int len = Val.length (); //Gets the length of the string
12. //Non-qualifying conditions
14. if (Radix < Character.min_radix | | radix > Character.max_radix)
16. throw New NumberFormatException ("Radix out of Range");
18. if (val.length () = = 0)
20. throw New NumberFormatException ("Zero length BigInteger");
22. //positive or negative, handle the "-" inside the string
24. Signum = 1;
26. int index = val.lastindexof ("-");
28. if (Index! =-1) {
30. if (index = = 0) {
32. if (val.length () = = 1)
34. throw New NumberFormatException ("Zero length BigInteger");
36. Signum =-1;
38. cursor = 1;
40. } Else {
42. throw New NumberFormatException ("illegal embedded minus sign");
44. }
46. }
48. //Skip the previous 0
50. While (cursor < len &&
52. Character.digit (Val.charat (cursor), radix) = = 0)
54. cursor++;
56. if (cursor = = len) {//If the string is all 0, it is stored as Zero.mag
58. Signum = 0;
60. Mag = Zero.mag;
62. return;
64. } Else {//numdigits is actually a valid number
66. Numdigits = Len-cursor;
68. }
70. how many bits will be required to convert the radix number of//numdigits bits into 2 binary
72. The elements in the//bitsperdigit array are multiplied by 1024 and need to be shifted right 10 bits (equivalent to dividing by 1024), when doing division there will be
74. //decimal loss, so add 1 to ensure that the number of digits must be sufficient
76. //An int has 32bit, so dividing by 32 is the size of the mag array we started estimating
78. int numbits = (int) (((Numdigits * Bitsperdigit[radix]) >>> ) + 1);
80. int numwords = (numbits + + )/32;
82. Mag = new int[numwords];
84. //start to intercept the number in the string according to Digitsperint
86. //Will not be enough Digitsperint[radix] first take out the conversion
88. int firstgrouplen = numdigits% digitsperint[radix];
90. if (Firstgrouplen = = 0)
92. Firstgrouplen = Digitsperint[radix];
94. //Put the number of the first paragraph in the last digit of the mag array
96. String Group = val.substring (cursor, cursor + = Firstgrouplen);
98. Mag[mag.length- 1] = Integer.parseint (group, Radix);
100. if (Mag[mag.length- 1] < 0)
102. throw New NumberFormatException ("illegal digit");
104. //The remaining segment conversion
106. int superradix = Intradix[radix];
108. int groupval = 0;
110. While (Cursor < val.length ()) {
112. Group = val.substring (cursor, cursor + + Digitsperint[radix]);
114. Groupval = Integer.parseint (group, Radix);
116. if (Groupval < 0)
118. throw New NumberFormatException ("illegal digit");
120. Destructivemuladd (Mag, Superradix, groupval);
122. }
124. Mag = trustedstripleadingzeroints (MAG);
128. }

The source code and analysis of BigInteger large number home law