package org.bouncycastle.asn1;

import java.io.ByteArrayOutputStream;
import java.io.IOException;

import org.bouncycastle.util.Arrays;

public class DERBitString
    extends ASN1Object
    implements DERString
{
    private static final char[]  table = { '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'A', 'B', 'C', 'D', 'E', 'F' };
    
    protected byte[]      data;
    protected int         padBits;

    
return the correct number of pad bits for a bit string defined in a 32 bit constant
/** * return the correct number of pad bits for a bit string defined in * a 32 bit constant */
static protected int getPadBits( int bitString) { int val = 0; for (int i = 3; i >= 0; i--) { // // this may look a little odd, but if it isn't done like this pre jdk1.2 // JVM's break! // if (i != 0) { if ((bitString >> (i * 8)) != 0) { val = (bitString >> (i * 8)) & 0xFF; break; } } else { if (bitString != 0) { val = bitString & 0xFF; break; } } } if (val == 0) { return 7; } int bits = 1; while (((val <<= 1) & 0xFF) != 0) { bits++; } return 8 - bits; }
return the correct number of bytes for a bit string defined in a 32 bit constant
/** * return the correct number of bytes for a bit string defined in * a 32 bit constant */
static protected byte[] getBytes(int bitString) { int bytes = 4; for (int i = 3; i >= 1; i--) { if ((bitString & (0xFF << (i * 8))) != 0) { break; } bytes--; } byte[] result = new byte[bytes]; for (int i = 0; i < bytes; i++) { result[i] = (byte) ((bitString >> (i * 8)) & 0xFF); } return result; }
return a Bit String from the passed in object
Throws:
  • IllegalArgumentException – if the object cannot be converted.
/** * return a Bit String from the passed in object * * @exception IllegalArgumentException if the object cannot be converted. */
public static DERBitString getInstance( Object obj) { if (obj == null || obj instanceof DERBitString) { return (DERBitString)obj; } throw new IllegalArgumentException("illegal object in getInstance: " + obj.getClass().getName()); }
return a Bit String from a tagged object.
Params:
  • obj – the tagged object holding the object we want
  • explicit – true if the object is meant to be explicitly tagged false otherwise.
Throws:
/** * return a Bit String from a tagged object. * * @param obj the tagged object holding the object we want * @param explicit true if the object is meant to be explicitly * tagged false otherwise. * @exception IllegalArgumentException if the tagged object cannot * be converted. */
public static DERBitString getInstance( ASN1TaggedObject obj, boolean explicit) { DERObject o = obj.getObject(); if (explicit || o instanceof DERBitString) { return getInstance(o); } else { return fromOctetString(((ASN1OctetString)o).getOctets()); } } protected DERBitString( byte data, int padBits) { this.data = new byte[1]; this.data[0] = data; this.padBits = padBits; }
Params:
  • data – the octets making up the bit string.
  • padBits – the number of extra bits at the end of the string.
/** * @param data the octets making up the bit string. * @param padBits the number of extra bits at the end of the string. */
public DERBitString( byte[] data, int padBits) { this.data = data; this.padBits = padBits; } public DERBitString( byte[] data) { this(data, 0); } public DERBitString( DEREncodable obj) { try { this.data = obj.getDERObject().getEncoded(ASN1Encodable.DER); this.padBits = 0; } catch (IOException e) { throw new IllegalArgumentException("Error processing object : " + e.toString()); } } public byte[] getBytes() { return data; } public int getPadBits() { return padBits; }
Returns:the value of the bit string as an int (truncating if necessary)
/** * @return the value of the bit string as an int (truncating if necessary) */
public int intValue() { int value = 0; for (int i = 0; i != data.length && i != 4; i++) { value |= (data[i] & 0xff) << (8 * i); } return value; } void encode( DEROutputStream out) throws IOException { byte[] bytes = new byte[getBytes().length + 1]; bytes[0] = (byte)getPadBits(); System.arraycopy(getBytes(), 0, bytes, 1, bytes.length - 1); out.writeEncoded(BIT_STRING, bytes); } public int hashCode() { return padBits ^ Arrays.hashCode(data); } protected boolean asn1Equals( DERObject o) { if (!(o instanceof DERBitString)) { return false; } DERBitString other = (DERBitString)o; return this.padBits == other.padBits && Arrays.areEqual(this.data, other.data); } public String getString() { StringBuffer buf = new StringBuffer("#"); ByteArrayOutputStream bOut = new ByteArrayOutputStream(); ASN1OutputStream aOut = new ASN1OutputStream(bOut); try { aOut.writeObject(this); } catch (IOException e) { throw new RuntimeException("internal error encoding BitString"); } byte[] string = bOut.toByteArray(); for (int i = 0; i != string.length; i++) { buf.append(table[(string[i] >>> 4) & 0xf]); buf.append(table[string[i] & 0xf]); } return buf.toString(); } public String toString() { return getString(); } static DERBitString fromOctetString(byte[] bytes) { if (bytes.length < 1) { throw new IllegalArgumentException("truncated BIT STRING detected"); } int padBits = bytes[0]; byte[] data = new byte[bytes.length - 1]; if (data.length != 0) { System.arraycopy(bytes, 1, data, 0, bytes.length - 1); } return new DERBitString(data, padBits); } }