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/*
 * BCJ filter for Itanium (IA-64) instructions
 *
 * Authors: Lasse Collin 
 *          Igor Pavlov 
 *
 * This file has been put into the public domain.
 * You can do whatever you want with this file.
 */

package org.tukaani.xz.simple;

public final class IA64 implements SimpleFilter {
    private static final int[] BRANCH_TABLE = {
            0, 0, 0, 0, 0, 0, 0, 0,
            0, 0, 0, 0, 0, 0, 0, 0,
            4, 4, 6, 6, 0, 0, 7, 7,
            4, 4, 0, 0, 4, 4, 0, 0 };

    private final boolean isEncoder;
    private int pos;

    public IA64(boolean isEncoder, int startPos) {
        this.isEncoder = isEncoder;
        pos = startPos;
    }

    public int code(byte[] buf, int off, int len) {
        int end = off + len - 16;
        int i;

        for (i = off; i <= end; i += 16) {
            int instrTemplate = buf[i] & 0x1F;
            int mask = BRANCH_TABLE[instrTemplate];

            for (int slot = 0, bitPos = 5; slot < 3; ++slot, bitPos += 41) {
                if (((mask >>> slot) & 1) == 0)
                    continue;

                int bytePos = bitPos >>> 3;
                int bitRes = bitPos & 7;

                long instr = 0;
                for (int j = 0; j < 6; ++j)
                    instr |= (buf[i + bytePos + j] & 0xFFL) << (8 * j);

                long instrNorm = instr >>> bitRes;

                if (((instrNorm >>> 37) & 0x0F) != 0x05
                        || ((instrNorm >>> 9) & 0x07) != 0x00)
                    continue;

                int src = (int)((instrNorm >>> 13) & 0x0FFFFF);
                src |= ((int)(instrNorm >>> 36) & 1) << 20;
                src <<= 4;

                int dest;
                if (isEncoder)
                    dest = src + (pos + i - off);
                else
                    dest = src - (pos + i - off);

                dest >>>= 4;

                instrNorm &= ~(0x8FFFFFL << 13);
                instrNorm |= (dest & 0x0FFFFFL) << 13;
                instrNorm |= (dest & 0x100000L) << (36 - 20);

                instr &= (1 << bitRes) - 1;
                instr |= instrNorm << bitRes;

                for (int j = 0; j < 6; ++j)
                    buf[i + bytePos + j] = (byte)(instr >>> (8 * j));
            }
        }

        i -= off;
        pos += i;
        return i;
    }
}