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A Java Optimization Framework
There is a newer version: 4.6.0
package soot.coffi;

/*-
 * #%L
 * Soot - a J*va Optimization Framework
 * %%
 * Copyright (C) 1997 Clark Verbrugge
 * %%
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU Lesser General Public License as
 * published by the Free Software Foundation, either version 2.1 of the
 * License, or (at your option) any later version.
 * 
 * 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 Lesser Public License for more details.
 * 
 * You should have received a copy of the GNU General Lesser Public
 * License along with this program.  If not, see
 * .
 * #L%
 */

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

/**
 * Instruction subclasses are used to represent parsed bytecode; each bytecode operation has a corresponding subclass of
 * Instruction.
 * 
 * Each subclass is derived from one of
 * 

 * Instruction
 * Instruction_noargs (an Instruction with no embedded arguments)
 * Instruction_byte (an Instruction with a single byte data argument)
 * Instruction_bytevar (a byte argument specifying a local variable)
 * Instruction_byteindex (a byte argument specifying a constant pool index)
 * Instruction_int (an Instruction with a single short data argument)
 * Instruction_intvar (a short argument specifying a local variable)
 * Instruction_intindex (a short argument specifying a constant pool index)
 * Instruction_intbranch (a short argument specifying a code offset)
 * Instruction_longbranch (an int argument specifying a code offset)
 * 
 *
 * @author Clark Verbrugge
 * @see Instruction
 * @see Instruction_noargs
 * @see Instruction_byte
 * @see Instruction_bytevar
 * @see Instruction_byteindex
 * @see Instruction_int
 * @see Instruction_intvar
 * @see Instruction_intindex
 * @see Instruction_intbranch
 * @see Instruction_longbranch
 * @see Instruction_Unknown
 */
class Instruction_Lookupswitch extends Instruction {
  private static final Logger logger = LoggerFactory.getLogger(Instruction_Lookupswitch.class);

  public Instruction_Lookupswitch() {
    super((byte) ByteCode.LOOKUPSWITCH);
    name = "lookupswitch";
    branches = true;
  }

  public byte pad; // number of bytes used for padding
  public int default_offset;
  public int npairs;
  public int match_offsets[];
  public Instruction default_inst;
  public Instruction match_insts[];

  public String toString(cp_info constant_pool[]) {
    // first figure out padding to next 4-byte quantity
    String args;
    int i;
    args = super.toString(constant_pool) + argsep + "(" + Integer.toString(pad) + ")";
    args = args + argsep + Integer.toString(default_inst.label);
    args = args + argsep + Integer.toString(npairs) + ": ";
    for (i = 0; i < npairs; i++) {
      args = args + "case " + Integer.toString(match_offsets[i * 2]) + ": label_" + Integer.toString(match_insts[i].label);
    }
    return args;
  }

  public int parse(byte bc[], int index) {
    // first figure out padding to next 4-byte quantity
    int i, j;
    i = index % 4;
    if (i != 0) {
      pad = (byte) (4 - i);
    } else {
      pad = (byte) 0;
    }
    index += pad;
    default_offset = getInt(bc, index);
    index += 4;
    npairs = getInt(bc, index);
    index += 4;
    if (npairs > 0) {
      match_offsets = new int[npairs * 2];
      j = 0;
      do {
        match_offsets[j] = getInt(bc, index);
        j++;
        index += 4;
        match_offsets[j] = getInt(bc, index);
        index += 4;
        j++;
      } while (j < npairs * 2);
    }
    return index;
  }

  public int nextOffset(int curr) {
    int i, siz = 0;
    i = (curr + 1) % 4;
    if (i != 0) {
      siz = (4 - i);
    }
    return (curr + siz + 9 + npairs * 8);
  }

  public int compile(byte bc[], int index) {
    int i;
    bc[index++] = code;
    // insert padding so next instruction is on a 4-byte boundary
    for (i = 0; i < pad; i++) {
      bc[index++] = 0;
    }
    if (default_inst != null) {
      index = intToBytes(default_inst.label - label, bc, index);
    } else {
      index = intToBytes(default_offset, bc, index);
    }
    index = intToBytes(npairs, bc, index);
    for (i = 0; i < npairs; i++) {
      index = intToBytes(match_offsets[i * 2], bc, index);
      if (match_insts[i] != null) {
        index = intToBytes((match_insts[i]).label - label, bc, index);
      } else {
        index = intToBytes(match_offsets[i * 2 + 1], bc, index);
      }
    }
    return index;
  }

  public void offsetToPointer(ByteCode bc) {
    int i;
    default_inst = bc.locateInst(default_offset + label);
    if (default_inst == null) {
      logger.warn("can't locate target of instruction");
      logger.debug(" which should be at byte address " + (label + default_offset));
    } else {
      default_inst.labelled = true;
    }
    if (npairs > 0) {
      match_insts = new Instruction[npairs];
      for (i = 0; i < npairs; i++) {
        match_insts[i] = bc.locateInst(match_offsets[i * 2 + 1] + label);
        if (match_insts[i] == null) {
          logger.warn("can't locate target of instruction");
          logger.debug(" which should be at byte address " + (label + match_offsets[i * 2 + 1]));
        } else {
          match_insts[i].labelled = true;
        }
      }
    }
  }

  public Instruction[] branchpoints(Instruction next) {
    Instruction i[] = new Instruction[npairs + 1];
    int j;
    i[0] = default_inst;
    for (j = 1; j < npairs + 1; j++) {
      i[j] = match_insts[j - 1];
    }
    return i;
  }
}