common_helper/src/main/java/com/xiongyingqi/util/MD5Crypt.java
static private final String to64(long v, int size) {
        StringBuffer result = new StringBuffer();

        while (--size >= 0) {
            result.append(itoa64.charAt((int) (v & 0x3f)));
            v >>>= 6;
        }

        return result.toString();
    }
static private final String to64(long v, int size) {
        StringBuffer result = new StringBuffer();

        while (--size >= 0) {
            result.append(itoa64.charAt((int) (v & 0x3f)));
            v >>>= 6;
        }

        return result.toString();
    }
Function to return a string from the set: A-Za-z0-9./

@param size Length of the string
@param v    value to be converted
@return A string of size (size) from the set A-Za-z0-9./