Android Byte Array Encode encode3to4(byte[] b4, byte[] threeBytes, int numSigBytes, int options)

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  5. encode3to4(byte[] b4, byte[] threeBytes, int numSigBytes, int options)

Description

Encodes up to the first three bytes of array threeBytes and returns a four-byte array in Base64 notation.

Parameter

Parameter Description
b4 A reusable byte array to reduce array instantiation
threeBytes the array to convert
numSigBytes the number of significant bytes in your array

Return

four byte array in Base64 notation.

Declaration 

private static byte[] encode3to4(byte[] b4, byte[] threeBytes,
        int numSigBytes, int options)

Method Source Code

//package com.java2s;

public class Main {
    /**//from ww  w . j  a v  a2s .  c om
     * Encode using Base64-like encoding that is URL- and Filename-safe as described
     * in Section 4 of RFC3548:
     * <a href="http://www.faqs.org/rfcs/rfc3548.html">http://www.faqs.org/rfcs/rfc3548.html</a>.
     * It is important to note that data encoded this way is <em>not</em> officially valid Base64,
     * or at the very least should not be called Base64 without also specifying that is
     * was encoded using the URL- and Filename-safe dialect.
     */
    public final static int URL_SAFE = 16;
    /**
     * Encode using the special "ordered" dialect of Base64 described here:
     * <a href="http://www.faqs.org/qa/rfcc-1940.html">http://www.faqs.org/qa/rfcc-1940.html</a>.
     */
    public final static int ORDERED = 32;
    /** The equals sign (=) as a byte. */
    private final static byte EQUALS_SIGN = (byte) '=';
    /** The 64 valid Base64 values. */
    /* Host platform me be something funny like EBCDIC, so we hardcode these values. */
    private final static byte[] _STANDARD_ALPHABET = { (byte) 'A',
            (byte) 'B', (byte) 'C', (byte) 'D', (byte) 'E', (byte) 'F',
            (byte) 'G', (byte) 'H', (byte) 'I', (byte) 'J', (byte) 'K',
            (byte) 'L', (byte) 'M', (byte) 'N', (byte) 'O', (byte) 'P',
            (byte) 'Q', (byte) 'R', (byte) 'S', (byte) 'T', (byte) 'U',
            (byte) 'V', (byte) 'W', (byte) 'X', (byte) 'Y', (byte) 'Z',
            (byte) 'a', (byte) 'b', (byte) 'c', (byte) 'd', (byte) 'e',
            (byte) 'f', (byte) 'g', (byte) 'h', (byte) 'i', (byte) 'j',
            (byte) 'k', (byte) 'l', (byte) 'm', (byte) 'n', (byte) 'o',
            (byte) 'p', (byte) 'q', (byte) 'r', (byte) 's', (byte) 't',
            (byte) 'u', (byte) 'v', (byte) 'w', (byte) 'x', (byte) 'y',
            (byte) 'z', (byte) '0', (byte) '1', (byte) '2', (byte) '3',
            (byte) '4', (byte) '5', (byte) '6', (byte) '7', (byte) '8',
            (byte) '9', (byte) '+', (byte) '/' };
    /**
     * Used in the URL- and Filename-safe dialect described in Section 4 of RFC3548:
     * <a href="http://www.faqs.org/rfcs/rfc3548.html">http://www.faqs.org/rfcs/rfc3548.html</a>.
     * Notice that the last two bytes become "hyphen" and "underscore" instead of "plus" and "slash."
     */
    private final static byte[] _URL_SAFE_ALPHABET = { (byte) 'A',
            (byte) 'B', (byte) 'C', (byte) 'D', (byte) 'E', (byte) 'F',
            (byte) 'G', (byte) 'H', (byte) 'I', (byte) 'J', (byte) 'K',
            (byte) 'L', (byte) 'M', (byte) 'N', (byte) 'O', (byte) 'P',
            (byte) 'Q', (byte) 'R', (byte) 'S', (byte) 'T', (byte) 'U',
            (byte) 'V', (byte) 'W', (byte) 'X', (byte) 'Y', (byte) 'Z',
            (byte) 'a', (byte) 'b', (byte) 'c', (byte) 'd', (byte) 'e',
            (byte) 'f', (byte) 'g', (byte) 'h', (byte) 'i', (byte) 'j',
            (byte) 'k', (byte) 'l', (byte) 'm', (byte) 'n', (byte) 'o',
            (byte) 'p', (byte) 'q', (byte) 'r', (byte) 's', (byte) 't',
            (byte) 'u', (byte) 'v', (byte) 'w', (byte) 'x', (byte) 'y',
            (byte) 'z', (byte) '0', (byte) '1', (byte) '2', (byte) '3',
            (byte) '4', (byte) '5', (byte) '6', (byte) '7', (byte) '8',
            (byte) '9', (byte) '-', (byte) '_' };
    /**
     * I don't get the point of this technique, but someone requested it,
     * and it is described here:
     * <a href="http://www.faqs.org/qa/rfcc-1940.html">http://www.faqs.org/qa/rfcc-1940.html</a>.
     */
    private final static byte[] _ORDERED_ALPHABET = { (byte) '-',
            (byte) '0', (byte) '1', (byte) '2', (byte) '3', (byte) '4',
            (byte) '5', (byte) '6', (byte) '7', (byte) '8', (byte) '9',
            (byte) 'A', (byte) 'B', (byte) 'C', (byte) 'D', (byte) 'E',
            (byte) 'F', (byte) 'G', (byte) 'H', (byte) 'I', (byte) 'J',
            (byte) 'K', (byte) 'L', (byte) 'M', (byte) 'N', (byte) 'O',
            (byte) 'P', (byte) 'Q', (byte) 'R', (byte) 'S', (byte) 'T',
            (byte) 'U', (byte) 'V', (byte) 'W', (byte) 'X', (byte) 'Y',
            (byte) 'Z', (byte) '_', (byte) 'a', (byte) 'b', (byte) 'c',
            (byte) 'd', (byte) 'e', (byte) 'f', (byte) 'g', (byte) 'h',
            (byte) 'i', (byte) 'j', (byte) 'k', (byte) 'l', (byte) 'm',
            (byte) 'n', (byte) 'o', (byte) 'p', (byte) 'q', (byte) 'r',
            (byte) 's', (byte) 't', (byte) 'u', (byte) 'v', (byte) 'w',
            (byte) 'x', (byte) 'y', (byte) 'z' };

    /**
     * Encodes up to the first three bytes of array <var>threeBytes</var>
     * and returns a four-byte array in Base64 notation.
     * The actual number of significant bytes in your array is
     * given by <var>numSigBytes</var>.
     * The array <var>threeBytes</var> needs only be as big as
     * <var>numSigBytes</var>.
     * Code can reuse a byte array by passing a four-byte array as <var>b4</var>.
     *
     * @param b4 A reusable byte array to reduce array instantiation
     * @param threeBytes the array to convert
     * @param numSigBytes the number of significant bytes in your array
     * @return four byte array in Base64 notation.
     * @since 1.5.1
     */
    private static byte[] encode3to4(byte[] b4, byte[] threeBytes,
            int numSigBytes, int options) {
        encode3to4(threeBytes, 0, numSigBytes, b4, 0, options);
        return b4;
    }

    /**
     * <p>Encodes up to three bytes of the array <var>source</var>
     * and writes the resulting four Base64 bytes 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 accomodate <var>srcOffset</var> + 3 for
     * the <var>source</var> array or <var>destOffset</var> + 4 for
     * the <var>destination</var> array.
     * The actual number of significant bytes in your array is
     * given by <var>numSigBytes</var>.</p>
     * <p>This is the lowest level of the encoding methods with
     * all possible parameters.</p>
     *
     * @param source the array to convert
     * @param srcOffset the index where conversion begins
     * @param numSigBytes the number of significant bytes in your array
     * @param destination the array to hold the conversion
     * @param destOffset the index where output will be put
     * @return the <var>destination</var> array
     * @since 1.3
     */
    private static byte[] encode3to4(byte[] source, int srcOffset,
            int numSigBytes, byte[] destination, int destOffset, int options) {

        byte[] ALPHABET = getAlphabet(options);

        //           1         2         3
        // 01234567890123456789012345678901 Bit position
        // --------000000001111111122222222 Array position from threeBytes
        // --------|    ||    ||    ||    | Six bit groups to index ALPHABET
        //          >>18  >>12  >> 6  >> 0  Right shift necessary
        //                0x3f  0x3f  0x3f  Additional AND

        // Create buffer with zero-padding if there are only one or two
        // significant bytes passed in the array.
        // We have to shift left 24 in order to flush out the 1's that appear
        // when Java treats a value as negative that is cast from a byte to an int.
        int inBuff = (numSigBytes > 0 ? ((source[srcOffset] << 24) >>> 8)
                : 0)
                | (numSigBytes > 1 ? ((source[srcOffset + 1] << 24) >>> 16)
                        : 0)
                | (numSigBytes > 2 ? ((source[srcOffset + 2] << 24) >>> 24)
                        : 0);

        switch (numSigBytes) {
        case 3:
            destination[destOffset] = ALPHABET[(inBuff >>> 18)];
            destination[destOffset + 1] = ALPHABET[(inBuff >>> 12) & 0x3f];
            destination[destOffset + 2] = ALPHABET[(inBuff >>> 6) & 0x3f];
            destination[destOffset + 3] = ALPHABET[(inBuff) & 0x3f];
            return destination;

        case 2:
            destination[destOffset] = ALPHABET[(inBuff >>> 18)];
            destination[destOffset + 1] = ALPHABET[(inBuff >>> 12) & 0x3f];
            destination[destOffset + 2] = ALPHABET[(inBuff >>> 6) & 0x3f];
            destination[destOffset + 3] = EQUALS_SIGN;
            return destination;

        case 1:
            destination[destOffset] = ALPHABET[(inBuff >>> 18)];
            destination[destOffset + 1] = ALPHABET[(inBuff >>> 12) & 0x3f];
            destination[destOffset + 2] = EQUALS_SIGN;
            destination[destOffset + 3] = EQUALS_SIGN;
            return destination;

        default:
            return destination;
        } // end switch
    }

    /**
     * Returns one of the _SOMETHING_ALPHABET byte arrays depending on
     * the options specified.
     * It's possible, though silly, to specify ORDERED <b>and</b> URLSAFE
     * in which case one of them will be picked, though there is
     * no guarantee as to which one will be picked.
     */
    private final static byte[] getAlphabet(int options) {
        if ((options & URL_SAFE) == URL_SAFE) {
            return _URL_SAFE_ALPHABET;
        } else if ((options & ORDERED) == ORDERED) {
            return _ORDERED_ALPHABET;
        } else {
            return _STANDARD_ALPHABET;
        }
    }
}

Related

  1. encodeToString(byte[] input, int flags)
  2. encodeToString(byte[] input, int offset, int len, int flags)
  3. encodeWebSafe(byte[] source, boolean doPadding)
  4. encodeWebSafe(byte[] source, boolean doPadding)
  5. encodeWebSafe(byte[] source, boolean doPadding)
  6. encode3to4(byte[] source, int srcOffset, int numSigBytes, byte[] destination, int destOffset, int options)
  7. putChar(byte[] bb, char ch, int index)
  8. putDouble(byte[] bb, double x, int index)
  9. putInt(int value, int offset, byte[] byteArr)