Android Byte Array Decode decode4to3(byte[] source, int srcOffset, byte[] destination, int destOffset, byte[] decodabet)

Description

Decodes four bytes from array source and writes the resulting bytes (up to three of them) to destination.

License

Apache License

Parameter

Parameter	Description
source	the array to convert
srcOffset	the index where conversion begins
destination	the array to hold the conversion
destOffset	the index where output will be put
decodabet	the decodabet for decoding Base64 content

Return

the number of decoded bytes converted

Declaration

private static int decode4to3(byte[] source, int srcOffset,
        byte[] destination, int destOffset, byte[] decodabet) 

Method Source Code

//package com.java2s;
// Licensed under the Apache License, Version 2.0 (the "License");

public class Main {
    /** The equals sign (=) as a byte. */
    private final static byte EQUALS_SIGN = (byte) '=';

    /**//from  www .  j a  va2 s . com
     * Decodes four bytes from array <var>source</var>
     * and writes the resulting bytes (up to three of them)
     * to <var>destination</var>.
     * The source and destination arrays can be manipulated
     * anywhere along their length by specifying
     * <var>srcOffset</var> and <var>destOffset</var>.
     * This method does not check to make sure your arrays
     * are large enough to accommodate <var>srcOffset</var> + 4 for
     * the <var>source</var> array or <var>destOffset</var> + 3 for
     * the <var>destination</var> array.
     * This method returns the actual number of bytes that
     * were converted from the Base64 encoding.
     *
     *
     * @param source the array to convert
     * @param srcOffset the index where conversion begins
     * @param destination the array to hold the conversion
     * @param destOffset the index where output will be put
     * @param decodabet the decodabet for decoding Base64 content
     * @return the number of decoded bytes converted
     * @since 1.3
     */
    private static int decode4to3(byte[] source, int srcOffset,
            byte[] destination, int destOffset, byte[] decodabet) {
        // Example: Dk==
        if (source[srcOffset + 2] == EQUALS_SIGN) {
            int outBuff = ((decodabet[source[srcOffset]] << 24) >>> 6)
                    | ((decodabet[source[srcOffset + 1]] << 24) >>> 12);

            destination[destOffset] = (byte) (outBuff >>> 16);
            return 1;
        } else if (source[srcOffset + 3] == EQUALS_SIGN) {
            // Example: DkL=
            int outBuff = ((decodabet[source[srcOffset]] << 24) >>> 6)
                    | ((decodabet[source[srcOffset + 1]] << 24) >>> 12)
                    | ((decodabet[source[srcOffset + 2]] << 24) >>> 18);

            destination[destOffset] = (byte) (outBuff >>> 16);
            destination[destOffset + 1] = (byte) (outBuff >>> 8);
            return 2;
        } else {
            // Example: DkLE
            int outBuff = ((decodabet[source[srcOffset]] << 24) >>> 6)
                    | ((decodabet[source[srcOffset + 1]] << 24) >>> 12)
                    | ((decodabet[source[srcOffset + 2]] << 24) >>> 18)
                    | ((decodabet[source[srcOffset + 3]] << 24) >>> 24);

            destination[destOffset] = (byte) (outBuff >> 16);
            destination[destOffset + 1] = (byte) (outBuff >> 8);
            destination[destOffset + 2] = (byte) (outBuff);
            return 3;
        }
    }
}

Related

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2. decode(byte[] source, int off, int len, byte[] decodabet)
3. decode(byte[] source, int off, int len, byte[] decodabet)
4. decode4to3(byte[] source, int srcOffset, byte[] destination, int destOffset, byte[] decodabet)
5. decode4to3(byte[] source, int srcOffset, byte[] destination, int destOffset, byte[] decodabet)
6. decodeWebSafe(String s)
7. decodeWebSafe(String s)
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