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/*
This file is part of GNUnet.
(C) 2011, 2012 Christian Grothoff (and other contributing authors)
GNUnet is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published
by the Free Software Foundation; either version 3, or (at your
option) any later version.
GNUnet is distributed in the hope that it will be useful, but
WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
General Public License for more details.
You should have received a copy of the GNU General Public License
along with GNUnet; see the file COPYING. If not, write to the
Free Software Foundation, Inc., 59 Temple Place - Suite 330,
Boston, MA 02111-1307, USA.
*/
package org.gnunet.util;
/**
* Common functions on Strings, specific to gnunet-java
*/
public class Strings {
private static final String encTable = "0123456789ABCDEFGHIJKLMNOPQRSTUV";
/**
* Convert binary data to ASCII encoding. The ASCII encoding is rather
* GNUnet specific. It was chosen such that it only uses characters
* in [0-9A-V], can be produced without complex arithmetics and uses a
* small number of characters.
* Does not append 0-terminator, but returns a pointer to the place where
* it should be placed, if needed.
*
* returned string has length ((size*8) + (((size*8) % 5) > 0 ? 5 - ((size*8) % 5) : 0)) / 5 bytes
*
* @param data data to encode
* @return pointer to the next byte in 'out' or NULL on error.
*/
public static String dataToString(byte[] data) {
StringBuilder sb = new StringBuilder();
long rpos = 0;
long bits = 0;
long vbit = 0;
long size = data.length;
while ((rpos < size) || (vbit > 0)) {
if ((rpos < size) && (vbit < 5)) {
byte b = data[(int) rpos++];
// convert double to int without sign extension
int s = b >= 0 ? b : (256 + b);
// eat 8 more bits
bits = (bits << 8) | s;
vbit += 8;
}
if (vbit < 5) {
// zero-padding
bits <<= (5 - vbit);
vbit = 5;
}
sb.append(encTable.charAt((int) (bits >>> (vbit - 5)) & 31));
vbit -= 5;
}
return sb.toString();
}
/**
* Convert ASCII encoding back to data
* out_size must match exactly the size of the data before it was encoded.
*
* @param string the string to decode
* @param outSize size of the output buffer
* @return GNUNET_OK on success, GNUNET_SYSERR if result has the wrong encoding
*/
public static byte[] stringToData(String string, int outSize) {
long rpos;
long wpos;
long bits;
long vbit;
long ret;
long shift;
int enclen = string.length();
int encoded_len = outSize * 8;
byte[] out = new byte[outSize];
if (encoded_len % 5 > 0) {
// padding!
vbit = encoded_len % 5;
shift = 5 - vbit;
} else {
vbit = 0;
shift = 0;
}
if ((encoded_len + shift) / 5 != enclen) {
throw new AssertionError();
}
wpos = outSize;
rpos = enclen;
bits = (ret = getValue__(string.charAt((int) (--rpos)))) >> (5 - encoded_len % 5);
if (-1 == ret) {
throw new AssertionError();
}
while (wpos > 0) {
assert rpos > 0;
bits = ((ret = getValue__(string.charAt((int) (--rpos)))) << vbit) | bits;
if (-1 == ret) {
throw new AssertionError();
}
vbit += 5;
if (vbit >= 8) {
out[(int)--wpos] = (byte)((char) bits);
bits >>= 8;
vbit -= 8;
}
}
assert(rpos == 0);
assert(vbit == 0);
return out;
}
private static int getValue__ (char a) {
if ((a >= '0') && (a <= '9')) {
return a - '0';
}
if ((a >= 'A') && (a <= 'V')) {
return (a - 'A' + 10);
}
return -1;
}
}
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