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/*
 * Copyright 2013-2014 Amazon.com, Inc. or its affiliates. All Rights Reserved.
 *
 * Licensed under the Apache License, Version 2.0 (the "License").
 * You may not use this file except in compliance with the License.
 * A copy of the License is located at
 *
 *  http://aws.amazon.com/apache2.0
 *
 * or in the "license" file accompanying this file. This file is distributed
 * on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either
 * express or implied. See the License for the specific language governing
 * permissions and limitations under the License.
 */
package com.amazonaws.util;

/**
 * A Base 16 codec implementation.
 * 
 * @author Hanson Char
 */
class Base16Codec implements Codec {
    private static final int OFFSET_OF_a = 'a' - 10;
    private static final int OFFSET_OF_A = 'A' - 10;
    private static final int MASK_4BITS = (1 << 4) - 1;

    private static class LazyHolder {
        private static final byte[] DECODED = decodeTable();
        
        private static byte[] decodeTable() {
            final byte[] dest = new byte['f'+1];
            
            for (int i=0; i <= 'f'; i++) 
            {
                if (i >= '0' && i <= '9')
                    dest[i] = (byte)(i - '0');
                else if (i >= 'A' && i <= 'F')
                    dest[i] = (byte)(i - OFFSET_OF_A);
                else if (i >= 'a' && i <= 'f')
                    dest[i] = (byte)(i - OFFSET_OF_a);
                else 
                    dest[i] = -1;
            }
            return dest;
        }
    }
    
    private final byte[] ALPAHBETS = CodecUtils.toBytesDirect("0123456789ABCDEF");

    @Override
    public byte[] encode(byte[] src) {
        byte[] dest = new byte[src.length * 2];
        byte p;

        for (int i=0,j=0; i < src.length; i++) {
            dest[j++] = (byte)ALPAHBETS[(p=src[i]) >>> 4 & MASK_4BITS]; 
            dest[j++] = (byte)ALPAHBETS[p & MASK_4BITS]; 
        }
        return dest;
    }
    
    @Override
    public byte[] decode(byte[] src, final int length) 
    {
        if (length % 2 != 0) {
            throw new IllegalArgumentException(
                "Input is expected to be encoded in multiple of 2 bytes but found: "
                + length
            );
        }
        final byte[] dest = new byte[length / 2];

        for (int i=0, j=0; j < dest.length; j++) 
        {
            dest[j] = (byte)
                    (
                        pos(src[i++]) << 4 | pos(src[i++])
                    )
                    ;
            
        }
        return dest;
    }
    
    protected int pos(byte in) {
        int pos = LazyHolder.DECODED[in];
        
        if (pos > -1)
            return pos;
        throw new IllegalArgumentException("Invalid base 16 character: \'" + (char)in + "\'");
    }
}