标准的base32编码和解码

public class Base32 {

    private static final String base32Chars =
             "ABCDEFGHIJKLMNOPQRSTUVWXYZ234567";
     private static final int[] base32Lookup = {
         0xFF, 0xFF, 0x1A, 0x1B, 0x1C, 0x1D, 0x1E, 0x1F, // '0', '1', '2', '3', '4', '5', '6', '7'
         0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, // '8', '9', ':', ';', '<', '=', '>', '?'
         0xFF, 0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, // '@', 'A', 'B', 'C', 'D', 'E', 'F', 'G'
         0x07, 0x08, 0x09, 0x0A, 0x0B, 0x0C, 0x0D, 0x0E, // 'H', 'I', 'J', 'K', 'L', 'M', 'N', 'O'
         0x0F, 0x10, 0x11, 0x12, 0x13, 0x14, 0x15, 0x16, // 'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W'
         0x17, 0x18, 0x19, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, // 'X', 'Y', 'Z', '[', '\', ']', '^', '_'
         0xFF, 0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, // '`', 'a', 'b', 'c', 'd', 'e', 'f', 'g'
         0x07, 0x08, 0x09, 0x0A, 0x0B, 0x0C, 0x0D, 0x0E, // 'h', 'i', 'j', 'k', 'l', 'm', 'n', 'o'
         0x0F, 0x10, 0x11, 0x12, 0x13, 0x14, 0x15, 0x16, // 'p', 'q', 'r', 's', 't', 'u', 'v', 'w'
         0x17, 0x18, 0x19, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF // 'x', 'y', 'z', '{', '|', '}', '~', 'DEL'
     };

    public static String encode(
             final byte[] bytes) {
         int i = 0, index = 0, digit = 0;
         int currByte, nextByte;
         StringBuffer base32 = new StringBuffer((bytes.length + 7) * 8 / 5);

        while (i < bytes.length) {
             currByte = (bytes[i] >= 0) ? bytes[i] : (bytes[i] + 256); // unsign

            /* Is the current digit going to span a byte boundary? */
             if (index > 3) {
                 if ((i + 1) < bytes.length) {
                     nextByte = (bytes[i + 1] >= 0) ? bytes[i + 1] : (bytes[i + 1] + 256);
                 } else {
                     nextByte = 0;
                 }

                digit = currByte & (0xFF >> index);
                 index = (index + 5) % 8;
                 digit <<= index;
                 digit |= nextByte >> (8 - index);
                 i++;
             } else {
                 digit = (currByte >> (8 - (index + 5))) & 0x1F;
                 index = (index + 5) % 8;
                 if (index == 0) {
                     i++;
                 }
             }
             base32.append(base32Chars.charAt(digit));
         }

        return base32.toString();
     }

    public static byte[] decode(
             final String base32) {
         int i, index, lookup, offset, digit;
         byte[] bytes = new byte[base32.length() * 5 / 8];

        for (i = 0, index = 0, offset = 0; i < base32.length(); i++) {
             lookup = base32.charAt(i) - '0';

            /* Skip chars outside the lookup table */
             if (lookup < 0 || lookup >= base32Lookup.length) {
                 continue;
             }

            digit = base32Lookup[lookup];

            /* If this digit is not in the table, ignore it */
             if (digit == 0xFF) {
                 continue;
             }

            if (index <= 3) {
                 index = (index + 5) % 8;
                 if (index == 0) {
                     bytes[offset] |= digit;
                     offset++;
                     if (offset >= bytes.length) {
                         break;
                     }
                 } else {
                     bytes[offset] |= digit << (8 - index);
                 }
             } else {
                 index = (index + 5) % 8;
                 bytes[offset] |= (digit >>> index);
                 offset++;

                if (offset >= bytes.length) {
                     break;
                 }
                 bytes[offset] |= digit << (8 - index);
             }
         }
         return bytes;
     }
}