Subversion Repositories splitter

/*
 * Copyright (C) 2017, Gerd Petermann
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 3 or
 * version 2 as published by the Free Software Foundation.
 *
 * This program is distributed in the hope that it will be useful, but
 * WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * General Public License for more details.
 */
package uk.me.parabola.splitter.tools;

import java.util.Arrays;

/**
 * A class to write the bitstream. Based on code in mkgmap.
 *
 * @author Steve Ratcliffe
 * @author Gerd Petermann
 */
public class BitWriter {
        // Choose so that chunks will not fill it.

        // The byte buffer and its current length (allocated length)
        private byte[] buf;  // The buffer
        private int bufsize;  // The allocated size

        /** The number of bits already used in the current byte of the buffer. */
        private int usedBits;
        /** The index of the current byte of the buffer. */
        private int index;
        private static final int BUFSIZE_INC = 50;
        private static final int INITIAL_BUF_SIZE = 20;  
       
        public BitWriter(int sizeInBytes) {
                bufsize = sizeInBytes;
                buf = new byte[bufsize];
        }

        public BitWriter() {
                this(INITIAL_BUF_SIZE);
        }

        public void clear() {
                Arrays.fill(buf, (byte) 0);
                index = 0;
                usedBits = 0;
        }

        /**
         * Put exactly one bit into the buffer.
         *
         * @param b The bottom bit of the integer is set at the current bit position.
         */
        private void put1(int b) {
                ensureSize(index + 1);

                // Get the remaining bits into the byte.
                int rem = usedBits;

                // Or it in, we are assuming that the position is never turned back.
                buf[index] |= (b & 0x1) << rem;
                usedBits++;
                if (usedBits == 8) {
                        index++;
                        usedBits = 0;
                }
        }
       
        public void put1(boolean b) {
                put1(b ? 1 : 0);
        }

        /**
         * Put a number of bits into the buffer, growing it if necessary.
         *
         * @param bval The bits to add, the lowest <b>n</b> bits will be added to
         * the buffer.
         * @param nb The number of bits.
         */
        public void putn(int bval, int nb) {
                assert nb >= 1 && nb <= 32;
                int val = nb < 32 ? bval & ((1<<nb) - 1) : bval;
                int n = nb;

                ensureSize(index + (usedBits + n + 7) / 8);
               
                int rem = usedBits;
                       
                // Get each affected byte and set bits into it until we are done.
                while (n > 0) {
                        buf[index] |= ((val << rem) & 0xff);

                        // Account for change so far
                        int nput = 8 - rem;
                        if (nput > n)
                                nput = n;
                        usedBits += nput;
                        if (usedBits >= 8) {
                                index++;
                                usedBits = 0;
                        }
                        // Shift down in preparation for next byte.
                        val >>>= nput;
                        rem = 0;
                        n -= nput;
                }
        }
       
        /**
         * Write a signed value. Caller must make sure that absolute value fits into
         * the given number of bits
         */

        public void sputn(final int bval, final int nb) {
                assert nb > 1 && nb <= 32;
                int top = 1 << (nb - 1);
                if (bval < 0) {
                        assert -bval <  top || top < 0;  
                        int v = (top + bval) | top;
                        putn(v, nb);
                } else {
                        assert bval < top || top < 0;
                        putn(bval, nb);
                }
        }
       
        /**
         * Write a signed value. If the value doesn't fit into nb bits, write one or more 1 << (nb-1)  
         * as a flag for extended range.
         */

        public void sputn2(final int bval, final int nb) {
                assert nb > 1 && nb <= 32;
                int top = 1 << (nb - 1);
                int mask = top - 1;
                int val = Math.abs(bval);
               
                if (bval == Integer.MIN_VALUE) {
                        // catch special case : Math.abs(Integer.MIN_VALUE) returns Integer.MIN_VALUE
                        putn(top, nb);
                        val = Math.abs(val - mask);
                }
                assert val >= 0;
                while (val > mask) {
                        putn(top, nb);
                        val -= mask;
                }
                if (bval < 0) {
                        putn((top - val) | top, nb);
                } else {
                        putn(val, nb);
                }
        }

        public byte[] getBytes() {
                return buf;
        }

        public int getBitPosition() {
                return index * 8 + usedBits;
        }
       
        /**
         * Get the number of bytes actually used to hold the bit stream. This therefore can be and usually
         * is less than the length of the buffer returned by {@link #getBytes()}.
         * @return Number of bytes required to hold the output.
         */
        public int getLength() {
                if (usedBits == 0)
                        return index;
                return index + 1;
        }

        /**
         * Set everything up so that the given size can be accommodated.
         * The buffer is re-sized if necessary.
         *
         * @param newlen The new length of the bit buffer in bytes.
         */
        private void ensureSize(int newlen) {
                if (newlen >= bufsize)
                        reallocBuffer();
        }

        /**
         * Reallocate the byte buffer.
         */
        private void reallocBuffer() {
                bufsize += BUFSIZE_INC;
                buf = Arrays.copyOf(buf, bufsize);
        }
}