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The AWS SDK for Java with support for OSGi. The AWS SDK for Java provides Java APIs for building software on AWS' cost-effective, scalable, and reliable infrastructure products. The AWS Java SDK allows developers to code against APIs for all of Amazon's infrastructure web services (Amazon S3, Amazon EC2, Amazon SQS, Amazon Relational Database Service, Amazon AutoScaling, etc).

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/*
 * Copyright 2013-2016 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[] alphabets;

    Base16Codec() {
        this(true);
    }

    Base16Codec(boolean upperCase) {
        this.alphabets = upperCase
                  ? CodecUtils.toBytesDirect("0123456789ABCDEF")
                  : 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)alphabets[(p=src[i]) >>> 4 & MASK_4BITS];
            dest[j++] = (byte)alphabets[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 + "\'");
    }
}