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/*
This file is part of GNUnet.
(C) 2014 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;
import com.google.common.base.Preconditions;
import java.math.BigInteger;
/**
* Helper class for BigIntegers.
*/
public class BigIntegers {
/**
* Serialize a BigInteger, but do not add an extra bit for a
* signRaw.
*
* @param bigInteger big integer to serialize
* @param bits how many bits should the binary representation have?
* rounded up to the next multiple of 8.
* @return big endian representation of the given BigInteger, without a signRaw bit
*/
public static byte[] serializeUnsigned(BigInteger bigInteger, int bits) {
byte[] bytes = bigInteger.toByteArray();
int start;
Preconditions.checkArgument(bigInteger.bitCount() <= bits);
// skip byte that was only added to fit the signRaw
if (bytes[0] == 0) {
start = 1;
} else {
start = 0;
}
byte[] fixedBytes = new byte[(bits + 7) / 8];
System.arraycopy(bytes, start, fixedBytes,
fixedBytes.length - bytes.length + start, bytes.length - start);
return fixedBytes;
}
}
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