uavstack-master/com.creditease.uav.fastjson/src/main/java/com/alibaba/fastjson/util/Base64.java
package com.alibaba.fastjson.util;

import java.util.Arrays;

/**
 *
 * @version 2.2
 * @author Mikael Grev Date: 2004-aug-02 Time: 11:31:11
 * @deprecated internal api, don't use.
 */
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 #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 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;
    }

    public static byte[] decodeFast(String 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.charAt(sIx)] < 0)
            sIx++;

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

        // get the padding count (=) (0, 1 or 2)
        int pad = chars.charAt(eIx) == '=' ? (chars.charAt(eIx - 1) == '=' ? 2 : 1) : 0; // Count '=' at end.
        int cCnt = eIx - sIx + 1; // Content count including possible separators
        int sepCnt = charsLen > 76 ? (chars.charAt(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.charAt(sIx++)] << 18 | IA[chars.charAt(sIx++)] << 12 | IA[chars.charAt(sIx++)] << 6 | IA[chars.charAt(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.charAt(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 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 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;
    }
}