Subversion Repositories mkgmap

/*
 * Copyright (C) 2007 Steve Ratcliffe
 *
 *  This program is free software; you can redistribute it and/or modify
 *  it under the terms of the GNU General Public License 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.
 *
 *
 * Author: Steve Ratcliffe
 * Create date: 03-Feb-2007
 */
package uk.me.parabola.imgfmt.sys;

import uk.me.parabola.log.Logger;

import java.nio.ByteBuffer;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;

/**
 * Holds block numbers for a file.  It is part of the directory.  For a file
 * that needs more than one block several directory entries exist.  Each of
 * these has the header with the file name etc. in it, but the first one has
 * extra flags and info.
 *
 * <p>What is important here is that only part of a full block is used to
 * hold block numbers.
 *
 * <p>The entries are 512 bytes regardless of the block size.
 *
 * @author Steve Ratcliffe
 */
class BlockTable {
        private static final Logger log = Logger.getLogger(BlockTable.class);

        // Offset of the block table in the directory entry block.
        private static final int BLOCKS_TABLE_START = 0x20;
        private static final int ENTRY_SIZE = 512;

        private static final int TABLE_SIZE = (ENTRY_SIZE - BLOCKS_TABLE_START)/2;
        //private final int tableSize;

        private int curroff;
        private final List<char[]> blocks;
        private char[] currTable;

        BlockTable() {
                blocks = new ArrayList<>(200);
        }

        /**
         * Write out the specified table to the given buffer.
         *
         * @param buf The buffer to write to.
         * @param n The number of the block table to write out.
         */
        public void writeTable(ByteBuffer buf, int n) {
                char[] cbuf = blocks.get(n);
                log.debug("block with length", cbuf.length);
                for (char c : cbuf) {
                        buf.putChar(c);
                }
        }

        /**
         * Read a block table from the given buffer.  The table is added to the
         * list.
         * @param buf The buffer to read from.
         */
        public void readTable(ByteBuffer buf) {
                buf.position(BLOCKS_TABLE_START);
                buf.limit(ENTRY_SIZE);

                char[] cbuf = newTable();
                for (int i = 0; i < cbuf.length; i++) {
                        char c = buf.getChar();
                        cbuf[i] = c;
                }
        }
       
        /**
         * Add the given block number to this directory.
         *
         * @param n The block number to add.
         */
        public void addBlock(int n) {
                char[] thisTable = currTable;
                if (curroff >= TABLE_SIZE  || currTable == null)
                        thisTable = newTable();

                thisTable[curroff++] = (char) n;
        }

        /**
         * Given a logical block number, return the physical block number.
         *
         * @param lblock The logical block number, ie with respect to the file.
         * @return The physical block number in the file system.
         */
        public int physFromLogical(int lblock) {
                int blockNum = lblock / TABLE_SIZE;
                int offset = lblock - blockNum * TABLE_SIZE;
                if (blockNum >= blocks.size())
                        return 0xffff;
               
                char[] cbuf = blocks.get(blockNum);
                return cbuf[offset];
        }

        /**
         * Get the number of block tables.  This is the number of blocks that
         * will be used in the on disk directory structure.
         *
         * @return The number of blocks tables.
         */
        public int getNBlockTables() {
                return blocks.size();
        }

        /**
         * Allocate a new block to hold more directory block numbers.
         *
         * @return Array for more numbers.
         */
        private char[] newTable() {
                char[] table = new char[TABLE_SIZE];
                Arrays.fill(table, (char) 0xffff);

                curroff = 0;
                blocks.add(table);
                currTable = table;

                return table;
        }
}