fast int to string

More fast int to string (in decimal base) implementation for Java. It uses external bytes buffer an it can be useful if need write number to stream as fast as possible.

 1 package cy6ergn0m;
 2
 3 /**
 4  *
 5  * @author cy6erGn0m cy6erGn0m at gmail dot com
 6  */
 7 public class NumbersChars {
 8
 9     final static int[] sizeTable = { 9, 99, 999, 9999, 99999, 999999, 9999999,
10                                      99999999, 999999999, Integer.MAX_VALUE
11     };
12
13     final static byte[] digits = {
14         '0', '1', '2', '3', '4', '5',
15         '6', '7', '8', '9', 'a', 'b',
16         'c', 'd', 'e', 'f', 'g', 'h',
17         'i', 'j', 'k', 'l', 'm', 'n',
18         'o', 'p', 'q', 'r', 's', 't',
19         'u', 'v', 'w', 'x', 'y', 'z'
20     };
21     final static byte[] DigitTens = {
22         '0', '0', '0', '0', '0', '0', '0', '0', '0', '0',
23         '1', '1', '1', '1', '1', '1', '1', '1', '1', '1',
24         '2', '2', '2', '2', '2', '2', '2', '2', '2', '2',
25         '3', '3', '3', '3', '3', '3', '3', '3', '3', '3',
26         '4', '4', '4', '4', '4', '4', '4', '4', '4', '4',
27         '5', '5', '5', '5', '5', '5', '5', '5', '5', '5',
28         '6', '6', '6', '6', '6', '6', '6', '6', '6', '6',
29         '7', '7', '7', '7', '7', '7', '7', '7', '7', '7',
30         '8', '8', '8', '8', '8', '8', '8', '8', '8', '8',
31         '9', '9', '9', '9', '9', '9', '9', '9', '9', '9',
32     };
33     final static byte[] DigitOnes = {
34         '0', '1', '2', '3', '4', '5', '6', '7', '8', '9',
35         '0', '1', '2', '3', '4', '5', '6', '7', '8', '9',
36         '0', '1', '2', '3', '4', '5', '6', '7', '8', '9',
37         '0', '1', '2', '3', '4', '5', '6', '7', '8', '9',
38         '0', '1', '2', '3', '4', '5', '6', '7', '8', '9',
39         '0', '1', '2', '3', '4', '5', '6', '7', '8', '9',
40         '0', '1', '2', '3', '4', '5', '6', '7', '8', '9',
41         '0', '1', '2', '3', '4', '5', '6', '7', '8', '9',
42         '0', '1', '2', '3', '4', '5', '6', '7', '8', '9',
43         '0', '1', '2', '3', '4', '5', '6', '7', '8', '9',
44     };
45
46     // Requires positive x
47     static int stringSize ( int x ) {
48         for ( int i = 0;; i++ )
49             if ( x <= sizeTable[i] )
50                 return i + 1;
51     }
52
53     static void getChars ( int i, int index, byte[] buf ) {
54         int q, r;
55         int charPos = index;
56         byte sign = 0;
57
58         if ( i < 0 ) {
59             sign = '-';
60             i = -i;
61         }
62
63         // Generate two digits per iteration
64         while ( i >= 65536 ) {
65             q = i / 100;
66             // really: r = i - (q * 100);
67             r = i - ( ( q << 6 ) + ( q << 5 ) + ( q << 2 ) );
68             i = q;
69             buf[--charPos] = DigitOnes[r];
70             buf[--charPos] = DigitTens[r];
71         }
72
73         // Fall thru to fast mode for smaller numbers
74         // assert(i <= 65536, i);
75         for (;;) {
76             q = ( i * 52429 ) >>> ( 16 + 3 );
77             r = i - ( ( q << 3 ) + ( q << 1 ) );  // r = i-(q*10) ...
78
79             buf[--charPos] = digits[r];
80             i = q;
81             if ( i == 0 )
82                 break;
83         }
84         if ( sign != 0 )
85             buf[--charPos] = sign;
86     }
87
88     public static int i2s ( int i, byte[] buffer ) {
89         int size = ( i < 0 ) ? stringSize( -i ) + 1 : stringSize( i );
90         if ( size > buffer.length )
91             throw new IllegalArgumentException( "buffer too small" );
92         getChars( i, size, buffer );
93         return size;
94     }
95
96 }
97
98