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The Apache Commons Codec package contains simple encoder and decoders for various formats such as Base64 and Hexadecimal. In addition to these widely used encoders and decoders, the codec package also maintains a collection of phonetic encoding utilities.

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/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License 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 org.apache.commons.codec.net;

import org.apache.commons.codec.DecoderException;

/**
 * Utility methods for this package.
 *
 * This class is immutable and thread-safe.
 *
 * @since 1.4
 */
class Utils {

    /**
     * Radix used in encoding and decoding.
     */
    private static final int RADIX = 16;

    /**
     * Returns the numeric value of the character {@code b} in radix 16.
     *
     * @param b
     *            The byte to be converted.
     * @return The numeric value represented by the character in radix 16.
     *
     * @throws DecoderException
     *             Thrown when the byte is not valid per {@link Character#digit(char,int)}
     */
    static int digit16(final byte b) throws DecoderException {
        final int i = Character.digit((char) b, RADIX);
        if (i == -1) {
            throw new DecoderException("Invalid URL encoding: not a valid digit (radix " + RADIX + "): " + b);
        }
        return i;
    }

    /**
     * Returns the upper case hex digit of the lower 4 bits of the int.
     *
     * @param b the input int
     * @return the upper case hex digit of the lower 4 bits of the int.
     */
    static char hexDigit(final int b) {
        return Character.toUpperCase(Character.forDigit(b & 0xF, RADIX));
    }

}