/src/main/java/com/alibaba/fastjson/util/Base64.java

package com.alibaba.fastjson.util;

import java.util.Arrays;

/**
 * A very fast and memory efficient class to encode and decode to and from BASE64 in full accordance with RFC 2045.<br>
 * <br>
 * On Windows XP sp1 with 1.4.2_04 and later ;), this encoder and decoder is about 10 times faster on small arrays (10 -
 * 1000 bytes) and 2-3 times as fast on larger arrays (10000 - 1000000 bytes) compared to
 * <code>sun.misc.Encoder()/Decoder()</code>.<br>
 * <br>
 * On byte arrays the encoder is about 20% faster than Jakarta Commons Base64 Codec for encode and about 50% faster for
 * decoding large arrays. This implementation is about twice as fast on very small arrays (&lt 30 bytes). If
 * source/destination is a <code>String</code> this version is about three times as fast due to the fact that the
 * Commons Codec result has to be recoded to a <code>String</code> from <code>byte[]</code>, which is very expensive.<br>
 * <br>
 * This encode/decode algorithm doesn't create any temporary arrays as many other codecs do, it only allocates the
 * resulting array. This produces less garbage and it is possible to handle arrays twice as large as algorithms that
 * create a temporary array. (E.g. Jakarta Commons Codec). It is unknown whether Sun's
 * <code>sun.misc.Encoder()/Decoder()</code> produce temporary arrays but since performance is quite low it probably
 * does.<br>
 * <br>
 * The encoder produces the same output as the Sun one except that the Sun's encoder appends a trailing line separator
 * if the last character isn't a pad. Unclear why but it only adds to the length and is probably a side effect. Both are
 * in conformance with RFC 2045 though.<br>
 * Commons codec seem to always att a trailing line separator.<br>
 * <br>
 * <b>Note!</b> The encode/decode method pairs (types) come in three versions with the <b>exact</b> same algorithm and
 * thus a lot of code redundancy. This is to not create any temporary arrays for transcoding to/from different format
 * types. The methods not used can simply be commented out.<br>
 * <br>
 * There is also a "fast" version of all decode methods that works the same way as the normal ones, but har a few
 * demands on the decoded input. Normally though, these fast verions should be used if the source if the input is known
 * and it hasn't bee tampered with.<br>
 * <br>
 * If you find the code useful or you find a bug, please send me a note at base64 @ miginfocom . com. Licence (BSD):
 * ============== Copyright (c) 2004, Mikael Grev, MiG InfoCom AB. (base64 @ miginfocom . com) All rights reserved.
 * Redistribution and use in source and binary forms, with or without modification, are permitted provided that the
 * following conditions are met: Redistributions of source code must retain the above copyright notice, this list of
 * conditions and the following disclaimer. Redistributions in binary form must reproduce the above copyright notice,
 * this list of conditions and the following disclaimer in the documentation and/or other materials provided with the
 * distribution. Neither the name of the MiG InfoCom AB nor the names of its contributors may be used to endorse or
 * promote products derived from this software without specific prior written permission. THIS SOFTWARE IS PROVIDED BY
 * THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
 * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
 * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS;
 * OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR
 * TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 * POSSIBILITY OF SUCH DAMAGE.
 * 
 * @version 2.2
 * @author Mikael Grev Date: 2004-aug-02 Time: 11:31:11
 */

public class Base64 {

    public static final char[] CA = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/".toCharArray();
    public static final int[]  IA = new int[256];
    static {
        Arrays.fill(IA, -1);
        for (int i = 0, iS = CA.length; i < iS; i++)
            IA[CA[i]] = i;
        IA['='] = 0;
    }

    /**
     * Decodes a BASE64 encoded char array that is known to be resonably well formatted. The method is about twice as
     * fast as {@link #decode(char[])}. The preconditions are:<br>
     * + The array must have a line length of 76 chars OR no line separators at all (one line).<br>
     * + Line separator must be "\r\n", as specified in RFC 2045 + The array must not contain illegal characters within
     * the encoded string<br>
     * + The array CAN have illegal characters at the beginning and end, those will be dealt with appropriately.<br>
     * 
     * @param chars The source array. Length 0 will return an empty array. <code>null</code> will throw an exception.
     * @return The decoded array of bytes. May be of length 0.
     */
    public final static byte[] decodeFast(char[] chars, int offset, int charsLen) {
        // Check special case
        if (charsLen == 0) {
            return new byte[0];
        }

        int sIx = offset, eIx = offset + charsLen - 1; // Start and end index after trimming.

        // Trim illegal chars from start
        while (sIx < eIx && IA[chars[sIx]] < 0)
            sIx++;

        // Trim illegal chars from end
        while (eIx > 0 && IA[chars[eIx]] < 0)
            eIx--;

        // get the padding count (=) (0, 1 or 2)
        int pad = chars[eIx] == '=' ? (chars[eIx - 1] == '=' ? 2 : 1) : 0; // Count '=' at end.
        int cCnt = eIx - sIx + 1; // Content count including possible separators
        int sepCnt = charsLen > 76 ? (chars[76] == '\r' ? cCnt / 78 : 0) << 1 : 0;

        int len = ((cCnt - sepCnt) * 6 >> 3) - pad; // The number of decoded bytes
        byte[] bytes = new byte[len]; // Preallocate byte[] of exact length

        // Decode all but the last 0 - 2 bytes.
        int d = 0;
        for (int cc = 0, eLen = (len / 3) * 3; d < eLen;) {
            // Assemble three bytes into an int from four "valid" characters.
            int i = IA[chars[sIx++]] << 18 | IA[chars[sIx++]] << 12 | IA[chars[sIx++]] << 6 | IA[chars[sIx++]];

            // Add the bytes
            bytes[d++] = (byte) (i >> 16);
            bytes[d++] = (byte) (i >> 8);
            bytes[d++] = (byte) i;

            // If line separator, jump over it.
            if (sepCnt > 0 && ++cc == 19) {
                sIx += 2;
                cc = 0;
            }
        }

        if (d < len) {
            // Decode last 1-3 bytes (incl '=') into 1-3 bytes
            int i = 0;
            for (int j = 0; sIx <= eIx - pad; j++)
                i |= IA[chars[sIx++]] << (18 - j * 6);

            for (int r = 16; d < len; r -= 8)
                bytes[d++] = (byte) (i >> r);
        }

        return bytes;
    }

    /**
     * Decodes a BASE64 encoded string that is known to be resonably well formatted. The method is about twice as fast
     * as {@link #decode(String)}. The preconditions are:<br>
     * + The array must have a line length of 76 chars OR no line separators at all (one line).<br>
     * + Line separator must be "\r\n", as specified in RFC 2045 + The array must not contain illegal characters within
     * the encoded string<br>
     * + The array CAN have illegal characters at the beginning and end, those will be dealt with appropriately.<br>
     * 
     * @param s The source string. Length 0 will return an empty array. <code>null</code> will throw an exception.
     * @return The decoded array of bytes. May be of length 0.
     */
    public final static byte[] decodeFast(String s) {
        // Check special case
        int sLen = s.length();
        if (sLen == 0) return new byte[0];

        int sIx = 0, eIx = sLen - 1; // Start and end index after trimming.

        // Trim illegal chars from start
        while (sIx < eIx && IA[s.charAt(sIx) & 0xff] < 0)
            sIx++;

        // Trim illegal chars from end
        while (eIx > 0 && IA[s.charAt(eIx) & 0xff] < 0)
            eIx--;

        // get the padding count (=) (0, 1 or 2)
        int pad = s.charAt(eIx) == '=' ? (s.charAt(eIx - 1) == '=' ? 2 : 1) : 0; // Count '=' at end.
        int cCnt = eIx - sIx + 1; // Content count including possible separators
        int sepCnt = sLen > 76 ? (s.charAt(76) == '\r' ? cCnt / 78 : 0) << 1 : 0;

        int len = ((cCnt - sepCnt) * 6 >> 3) - pad; // The number of decoded bytes
        byte[] dArr = new byte[len]; // Preallocate byte[] of exact length

        // Decode all but the last 0 - 2 bytes.
        int d = 0;
        for (int cc = 0, eLen = (len / 3) * 3; d < eLen;) {
            // Assemble three bytes into an int from four "valid" characters.
            int i = IA[s.charAt(sIx++)] << 18 | IA[s.charAt(sIx++)] << 12 | IA[s.charAt(sIx++)] << 6
                    | IA[s.charAt(sIx++)];

            // Add the bytes
            dArr[d++] = (byte) (i >> 16);
            dArr[d++] = (byte) (i >> 8);
            dArr[d++] = (byte) i;

            // If line separator, jump over it.
            if (sepCnt > 0 && ++cc == 19) {
                sIx += 2;
                cc = 0;
            }
        }

        if (d < len) {
            // Decode last 1-3 bytes (incl '=') into 1-3 bytes
            int i = 0;
            for (int j = 0; sIx <= eIx - pad; j++)
                i |= IA[s.charAt(sIx++)] << (18 - j * 6);

            for (int r = 16; d < len; r -= 8)
                dArr[d++] = (byte) (i >> r);
        }

        return dArr;
    }
}