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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.digest;

import java.util.Random;

/**
 * Base64 like method to convert binary bytes into ASCII chars.
 *
 * TODO: Can Base64 be reused?
 *
 * 
 * This class is immutable and thread-safe.
 * 
 *
 * @version $Id: B64.java 1435550 2013-01-19 14:09:52Z tn $
 * @since 1.7
 */
class B64 {

    /**
     * Table with characters for Base64 transformation.
     */
    static final String B64T = "./0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz";

    /**
     * Base64 like conversion of bytes to ASCII chars.
     *
     * @param b2
     *            A byte from the result.
     * @param b1
     *            A byte from the result.
     * @param b0
     *            A byte from the result.
     * @param outLen
     *            The number of expected output chars.
     * @param buffer
     *            Where the output chars is appended to.
     */
    static void b64from24bit(final byte b2, final byte b1, final byte b0, final int outLen,
                             final StringBuilder buffer) {
        // The bit masking is necessary because the JVM byte type is signed!
        int w = ((b2 << 16) & 0x00ffffff) | ((b1 << 8) & 0x00ffff) | (b0 & 0xff);
        // It's effectively a "for" loop but kept to resemble the original C code.
        int n = outLen;
        while (n-- > 0) {
            buffer.append(B64T.charAt(w & 0x3f));
            w >>= 6;
        }
    }

    /**
     * Generates a string of random chars from the B64T set.
     *
     * @param num
     *            Number of chars to generate.
     */
    static String getRandomSalt(final int num) {
        final StringBuilder saltString = new StringBuilder();
        for (int i = 1; i <= num; i++) {
            saltString.append(B64T.charAt(new Random().nextInt(B64T.length())));
        }
        return saltString.toString();
    }
}