/*
 * reserved comment block
 * DO NOT REMOVE OR ALTER!
 */
/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.sun.org.apache.bcel.internal.classfile;


import com.sun.org.apache.bcel.internal.Constants;
import com.sun.org.apache.bcel.internal.util.ByteSequence;
import java.io.*;
import java.util.ArrayList;
import java.util.zip.*;

Utility functions that do not really belong to any class in particular.
Author:
 M. Dahm/**
 * Utility functions that do not really belong to any class in particular.
 *
 * @author  <A HREF="mailto:markus.dahm@berlin.de">M. Dahm</A>
 */
public abstract class Utility {
  private static int consumed_chars; /* How many chars have been consumed
                                      * during parsing in signatureToString().
                                      * Read by methodSignatureToString().
                                      * Set by side effect,but only internally.
                                      */
  private static boolean wide=false; /* The `WIDE' instruction is used in the
                                      * byte code to allow 16-bit wide indices
                                      * for local variables. This opcode
                                      * precedes an `ILOAD', e.g.. The opcode
                                      * immediately following takes an extra
                                      * byte which is combined with the
                                      * following byte to form a
                                      * 16-bit value.
                                      */
  
Convert bit field of flags into string such as `static final'.
Params:
access_flags – Access flags
Returns:
String representation of flags/**
   * Convert bit field of flags into string such as `static final'.
   *
   * @param  access_flags Access flags
   * @return String representation of flags
   */
  public static final String accessToString(int access_flags) {
    return accessToString(access_flags, false);
  }

  
Convert bit field of flags into string such as `static final'.
Special case: Classes compiled with new compilers and with the
`ACC_SUPER' flag would be said to be "synchronized". This is
because SUN used the same value for the flags `ACC_SUPER' and
`ACC_SYNCHRONIZED'.
Params:
access_flags – Access flags
for_class – access flags are for class qualifiers ?
Returns:
String representation of flags/**
   * Convert bit field of flags into string such as `static final'.
   *
   * Special case: Classes compiled with new compilers and with the
   * `ACC_SUPER' flag would be said to be "synchronized". This is
   * because SUN used the same value for the flags `ACC_SUPER' and
   * `ACC_SYNCHRONIZED'.
   *
   * @param  access_flags Access flags
   * @param  for_class access flags are for class qualifiers ?
   * @return String representation of flags
   */
  public static final String accessToString(int access_flags,
                                            boolean for_class)
  {
    StringBuffer buf = new StringBuffer();

    int p = 0;
    for(int i=0; p < Constants.MAX_ACC_FLAG; i++) { // Loop through known flags
      p = pow2(i);

      if((access_flags & p) != 0) {
        /* Special case: Classes compiled with new compilers and with the
         * `ACC_SUPER' flag would be said to be "synchronized". This is
         * because SUN used the same value for the flags `ACC_SUPER' and
         * `ACC_SYNCHRONIZED'.
         */
        if(for_class && ((p == Constants.ACC_SUPER) || (p == Constants.ACC_INTERFACE)))
          continue;

        buf.append(Constants.ACCESS_NAMES[i] + " ");
      }
    }

    return buf.toString().trim();
  }

  
Returns:
"class" or "interface", depending on the ACC_INTERFACE flag/**
   * @return "class" or "interface", depending on the ACC_INTERFACE flag
   */
  public static final String classOrInterface(int access_flags) {
    return ((access_flags & Constants.ACC_INTERFACE) != 0)? "interface" : "class";
  }

  
Disassemble a byte array of JVM byte codes starting from code line
`index' and return the disassembled string representation. Decode only
`num' opcodes (including their operands), use -1 if you want to
decompile everything.
Params:
code – byte code array
constant_pool – Array of constants
index – offset in `code' array
(number of opcodes, not bytes!)
length – number of opcodes to decompile, -1 for all
verbose – be verbose, e.g. print constant pool index
Returns:
String representation of byte codes/**
   * Disassemble a byte array of JVM byte codes starting from code line
   * `index' and return the disassembled string representation. Decode only
   * `num' opcodes (including their operands), use -1 if you want to
   * decompile everything.
   *
   * @param  code byte code array
   * @param  constant_pool Array of constants
   * @param  index offset in `code' array
   * <EM>(number of opcodes, not bytes!)</EM>
   * @param  length number of opcodes to decompile, -1 for all
   * @param  verbose be verbose, e.g. print constant pool index
   * @return String representation of byte codes
   */
  public static final String codeToString(byte[] code,
                                          ConstantPool constant_pool,
                                          int index, int length, boolean verbose)
  {
    StringBuffer buf    = new StringBuffer(code.length * 20); // Should be sufficient
    ByteSequence stream = new ByteSequence(code);

    try {
      for(int i=0; i < index; i++) // Skip `index' lines of code
        codeToString(stream, constant_pool, verbose);

      for(int i=0; stream.available() > 0; i++) {
        if((length < 0) || (i < length)) {
          String indices = fillup(stream.getIndex() + ":", 6, true, ' ');
          buf.append(indices + codeToString(stream, constant_pool, verbose) + '\n');
        }
      }
    } catch(IOException e) {
      System.out.println(buf.toString());
      e.printStackTrace();
      throw new ClassFormatException("Byte code error: " + e);
    }

    return buf.toString();
  }

  public static final String codeToString(byte[] code,
                                          ConstantPool constant_pool,
                                          int index, int length) {
    return codeToString(code, constant_pool, index, length, true);
  }

  
Disassemble a stream of byte codes and return the
string representation.
Params:
bytes – stream of bytes
constant_pool – Array of constants
verbose – be verbose, e.g. print constant pool index
Returns:
String representation of byte code/**
   * Disassemble a stream of byte codes and return the
   * string representation.
   *
   * @param  bytes stream of bytes
   * @param  constant_pool Array of constants
   * @param  verbose be verbose, e.g. print constant pool index
   * @return String representation of byte code
   */
  public static final String codeToString(ByteSequence bytes,
                                          ConstantPool constant_pool, boolean verbose)
       throws IOException
  {
    short        opcode = (short)bytes.readUnsignedByte();
    int          default_offset=0, low, high, npairs;
    int          index, vindex, constant;
    int[]        match, jump_table;
    int          no_pad_bytes=0, offset;
    StringBuffer buf = new StringBuffer(Constants.OPCODE_NAMES[opcode]);

    /* Special case: Skip (0-3) padding bytes, i.e., the
     * following bytes are 4-byte-aligned
     */
    if((opcode == Constants.TABLESWITCH) || (opcode == Constants.LOOKUPSWITCH)) {
      int remainder = bytes.getIndex() % 4;
      no_pad_bytes  = (remainder == 0)? 0 : 4 - remainder;

      for(int i=0; i < no_pad_bytes; i++) {
        byte b;

        if((b=bytes.readByte()) != 0)
          System.err.println("Warning: Padding byte != 0 in " +
                             Constants.OPCODE_NAMES[opcode] + ":" + b);
      }

      // Both cases have a field default_offset in common
      default_offset = bytes.readInt();
    }

    switch(opcode) {
      /* Table switch has variable length arguments.
       */
    case Constants.TABLESWITCH:
      low  = bytes.readInt();
      high = bytes.readInt();

      offset = bytes.getIndex() - 12 - no_pad_bytes - 1;
      default_offset += offset;

      buf.append("\tdefault = " + default_offset + ", low = " + low +
                 ", high = " + high + "(");

      jump_table = new int[high - low + 1];
      for(int i=0; i < jump_table.length; i++) {
        jump_table[i] = offset + bytes.readInt();
        buf.append(jump_table[i]);

        if(i < jump_table.length - 1)
          buf.append(", ");
      }
      buf.append(")");

      break;

      /* Lookup switch has variable length arguments.
       */
    case Constants.LOOKUPSWITCH: {

      npairs = bytes.readInt();
      offset = bytes.getIndex() - 8 - no_pad_bytes - 1;

      match      = new int[npairs];
      jump_table = new int[npairs];
      default_offset += offset;

      buf.append("\tdefault = " + default_offset + ", npairs = " + npairs +
                 " (");

      for(int i=0; i < npairs; i++) {
        match[i]      = bytes.readInt();

        jump_table[i] = offset + bytes.readInt();

        buf.append("(" + match[i] + ", " + jump_table[i] + ")");

        if(i < npairs - 1)
          buf.append(", ");
      }
      buf.append(")");
    }
    break;

    /* Two address bytes + offset from start of byte stream form the
     * jump target
     */
    case Constants.GOTO:      case Constants.IFEQ:      case Constants.IFGE:      case Constants.IFGT:
    case Constants.IFLE:      case Constants.IFLT:      case Constants.JSR: case Constants.IFNE:
    case Constants.IFNONNULL: case Constants.IFNULL:    case Constants.IF_ACMPEQ:
    case Constants.IF_ACMPNE: case Constants.IF_ICMPEQ: case Constants.IF_ICMPGE: case Constants.IF_ICMPGT:
    case Constants.IF_ICMPLE: case Constants.IF_ICMPLT: case Constants.IF_ICMPNE:
      buf.append("\t\t#" + ((bytes.getIndex() - 1) + bytes.readShort()));
      break;

      /* 32-bit wide jumps
       */
    case Constants.GOTO_W: case Constants.JSR_W:
      buf.append("\t\t#" + ((bytes.getIndex() - 1) + bytes.readInt()));
      break;

      /* Index byte references local variable (register)
       */
    case Constants.ALOAD:  case Constants.ASTORE: case Constants.DLOAD:  case Constants.DSTORE: case Constants.FLOAD:
    case Constants.FSTORE: case Constants.ILOAD:  case Constants.ISTORE: case Constants.LLOAD:  case Constants.LSTORE:
    case Constants.RET:
      if(wide) {
        vindex = bytes.readUnsignedShort();
        wide=false; // Clear flag
      }
      else
        vindex = bytes.readUnsignedByte();

      buf.append("\t\t%" + vindex);
      break;

      /*
       * Remember wide byte which is used to form a 16-bit address in the
       * following instruction. Relies on that the method is called again with
       * the following opcode.
       */
    case Constants.WIDE:
      wide      = true;
      buf.append("\t(wide)");
      break;

      /* Array of basic type.
       */
    case Constants.NEWARRAY:
      buf.append("\t\t<" + Constants.TYPE_NAMES[bytes.readByte()] + ">");
      break;

      /* Access object/class fields.
       */
    case Constants.GETFIELD: case Constants.GETSTATIC: case Constants.PUTFIELD: case Constants.PUTSTATIC:
      index = bytes.readUnsignedShort();
      buf.append("\t\t" +
                 constant_pool.constantToString(index, Constants.CONSTANT_Fieldref) +
                 (verbose? " (" + index + ")" : ""));
      break;

      /* Operands are references to classes in constant pool
       */
    case Constants.NEW:
    case Constants.CHECKCAST:
      buf.append("\t");
    case Constants.INSTANCEOF:
      index = bytes.readUnsignedShort();
      buf.append("\t<" + constant_pool.constantToString(index,
                                                        Constants.CONSTANT_Class) +
                 ">" + (verbose? " (" + index + ")" : ""));
      break;

      /* Operands are references to methods in constant pool
       */
    case Constants.INVOKESPECIAL: case Constants.INVOKESTATIC: case Constants.INVOKEVIRTUAL:
      index = bytes.readUnsignedShort();
      buf.append("\t" + constant_pool.constantToString(index,
                                                       Constants.CONSTANT_Methodref) +
                 (verbose? " (" + index + ")" : ""));
      break;

    case Constants.INVOKEINTERFACE:
      index = bytes.readUnsignedShort();
      int nargs = bytes.readUnsignedByte(); // historical, redundant
      buf.append("\t" +
                 constant_pool.constantToString(index,
                                                Constants.CONSTANT_InterfaceMethodref) +
                 (verbose? " (" + index + ")\t" : "") + nargs + "\t" +
                 bytes.readUnsignedByte()); // Last byte is a reserved space
      break;

      /* Operands are references to items in constant pool
       */
    case Constants.LDC_W: case Constants.LDC2_W:
      index = bytes.readUnsignedShort();

      buf.append("\t\t" + constant_pool.constantToString
                 (index, constant_pool.getConstant(index).getTag()) +
                 (verbose? " (" + index + ")" : ""));
      break;

    case Constants.LDC:
      index = bytes.readUnsignedByte();

      buf.append("\t\t" +
                 constant_pool.constantToString
                 (index, constant_pool.getConstant(index).getTag()) +
                 (verbose? " (" + index + ")" : ""));
      break;

      /* Array of references.
       */
    case Constants.ANEWARRAY:
      index = bytes.readUnsignedShort();

      buf.append("\t\t<" + compactClassName(constant_pool.getConstantString
                                          (index, Constants.CONSTANT_Class), false) +
                 ">" + (verbose? " (" + index + ")": ""));
      break;

      /* Multidimensional array of references.
       */
    case Constants.MULTIANEWARRAY: {
      index          = bytes.readUnsignedShort();
      int dimensions = bytes.readUnsignedByte();

      buf.append("\t<" + compactClassName(constant_pool.getConstantString
                                          (index, Constants.CONSTANT_Class), false) +
                 ">\t" + dimensions + (verbose? " (" + index + ")" : ""));
    }
    break;

    /* Increment local variable.
     */
    case Constants.IINC:
      if(wide) {
        vindex   = bytes.readUnsignedShort();
        constant = bytes.readShort();
        wide     = false;
      }
      else {
        vindex   = bytes.readUnsignedByte();
        constant = bytes.readByte();
      }
      buf.append("\t\t%" + vindex + "\t" + constant);
      break;

    default:
      if(Constants.NO_OF_OPERANDS[opcode] > 0) {
        for(int i=0; i < Constants.TYPE_OF_OPERANDS[opcode].length; i++) {
          buf.append("\t\t");
          switch(Constants.TYPE_OF_OPERANDS[opcode][i]) {
          case Constants.T_BYTE:  buf.append(bytes.readByte()); break;
          case Constants.T_SHORT: buf.append(bytes.readShort());       break;
          case Constants.T_INT:   buf.append(bytes.readInt());         break;

          default: // Never reached
            System.err.println("Unreachable default case reached!");
            buf.setLength(0);
          }
        }
      }
    }

    return buf.toString();
  }

  public static final String codeToString(ByteSequence bytes, ConstantPool constant_pool)
    throws IOException
  {
    return codeToString(bytes, constant_pool, true);
  }

  
Shorten long class names, java/lang/String becomes
String.
Params:
str – The long class name
Returns:
Compacted class name/**
   * Shorten long class names, <em>java/lang/String</em> becomes
   * <em>String</em>.
   *
   * @param str The long class name
   * @return Compacted class name
   */
  public static final String compactClassName(String str) {
    return compactClassName(str, true);
  }

  
Shorten long class name str, i.e., chop off the prefix,
if the
class name starts with this string and the flag chopit is true.
Slashes / are converted to dots ..
Params:
str – The long class name
prefix – The prefix the get rid off
chopit – Flag that determines whether chopping is executed or not
Returns:
Compacted class name/**
   * Shorten long class name <em>str</em>, i.e., chop off the <em>prefix</em>,
   * if the
   * class name starts with this string and the flag <em>chopit</em> is true.
   * Slashes <em>/</em> are converted to dots <em>.</em>.
   *
   * @param str The long class name
   * @param prefix The prefix the get rid off
   * @param chopit Flag that determines whether chopping is executed or not
   * @return Compacted class name
   */
  public static final String compactClassName(String str,
                                              String prefix,
                                              boolean chopit)
  {
    int len = prefix.length();

    str = str.replace('/', '.'); // Is `/' on all systems, even DOS

    if(chopit) {
      // If string starts with `prefix' and contains no further dots
      if(str.startsWith(prefix) &&
         (str.substring(len).indexOf('.') == -1))
        str = str.substring(len);
    }

    return str;
  }

  
Shorten long class names, java/lang/String becomes
java.lang.String,
e.g.. If chopit is true the prefix java.lang
is also removed.
Params:
str – The long class name
chopit – Flag that determines whether chopping is executed or not
Returns:
Compacted class name/**
   * Shorten long class names, <em>java/lang/String</em> becomes
   * <em>java.lang.String</em>,
   * e.g.. If <em>chopit</em> is <em>true</em> the prefix <em>java.lang</em>
   * is also removed.
   *
   * @param str The long class name
   * @param chopit Flag that determines whether chopping is executed or not
   * @return Compacted class name
   */
  public static final String compactClassName(String str, boolean chopit) {
    return compactClassName(str, "java.lang.", chopit);
  }

  private static final boolean is_digit(char ch) {
    return (ch >= '0') && (ch <= '9');
  }

  private static final boolean is_space(char ch) {
    return (ch == ' ') || (ch == '\t') || (ch == '\r') || (ch == '\n');
  }

  
Returns:
`flag' with bit `i' set to 1/**
   * @return `flag' with bit `i' set to 1
   */
  public static final int setBit(int flag, int i) {
    return flag | pow2(i);
  }

  
Returns:
`flag' with bit `i' set to 0/**
   * @return `flag' with bit `i' set to 0
   */
  public static final int clearBit(int flag, int i) {
    int bit = pow2(i);
    return (flag & bit) == 0? flag : flag ^ bit;
  }

  
Returns:
true, if bit `i' in `flag' is set/**
   * @return true, if bit `i' in `flag' is set
   */
  public static final boolean isSet(int flag, int i) {
    return (flag & pow2(i)) != 0;
  }

  
Converts string containing the method return and argument types
to a byte code method signature.
Params:
ret – Return type of method
argv – Types of method arguments
Returns:
Byte code representation of method signature/**
   * Converts string containing the method return and argument types
   * to a byte code method signature.
   *
   * @param  ret Return type of method
   * @param  argv Types of method arguments
   * @return Byte code representation of method signature
   */
  public final static String methodTypeToSignature(String ret, String[] argv)
    throws ClassFormatException
  {
    StringBuffer buf = new StringBuffer("(");
    String       str;

    if(argv != null)
      for(int i=0; i < argv.length; i++) {
        str = getSignature(argv[i]);

        if(str.endsWith("V")) // void can't be a method argument
          throw new ClassFormatException("Invalid type: " + argv[i]);

        buf.append(str);
      }

    str = getSignature(ret);

    buf.append(")" + str);

    return buf.toString();
  }

  
Params:
signature –    Method signature
Throws:
ClassFormatException – 
Returns:
Array of argument types/**
   * @param  signature    Method signature
   * @return Array of argument types
   * @throws  ClassFormatException
   */
  public static final String[] methodSignatureArgumentTypes(String signature)
    throws ClassFormatException
  {
    return methodSignatureArgumentTypes(signature, true);
  }

  
Params:
signature –    Method signature
chopit – Shorten class names ?
Throws:
ClassFormatException – 
Returns:
Array of argument types/**
   * @param  signature    Method signature
   * @param chopit Shorten class names ?
   * @return Array of argument types
   * @throws  ClassFormatException
   */
  public static final String[] methodSignatureArgumentTypes(String signature,
                                                            boolean chopit)
    throws ClassFormatException
  {
    ArrayList vec = new ArrayList();
    int       index;
    String[]  types;

    try { // Read all declarations between for `(' and `)'
      if(signature.charAt(0) != '(')
        throw new ClassFormatException("Invalid method signature: " + signature);

      index = 1; // current string position

      while(signature.charAt(index) != ')') {
        vec.add(signatureToString(signature.substring(index), chopit));
        index += consumed_chars; // update position
      }
    } catch(StringIndexOutOfBoundsException e) { // Should never occur
      throw new ClassFormatException("Invalid method signature: " + signature);
    }

    types = new String[vec.size()];
    vec.toArray(types);
    return types;
  }
  
Params:
signature –    Method signature
Throws:
ClassFormatException – 
Returns:
return type of method/**
   * @param  signature    Method signature
   * @return return type of method
   * @throws  ClassFormatException
   */
  public static final String methodSignatureReturnType(String signature)
       throws ClassFormatException
  {
    return methodSignatureReturnType(signature, true);
  }
  
Params:
signature –    Method signature
chopit – Shorten class names ?
Throws:
ClassFormatException – 
Returns:
return type of method/**
   * @param  signature    Method signature
   * @param chopit Shorten class names ?
   * @return return type of method
   * @throws  ClassFormatException
   */
  public static final String methodSignatureReturnType(String signature,
                                                       boolean chopit)
       throws ClassFormatException
  {
    int    index;
    String type;

    try {
      // Read return type after `)'
      index = signature.lastIndexOf(')') + 1;
      type = signatureToString(signature.substring(index), chopit);
    } catch(StringIndexOutOfBoundsException e) { // Should never occur
      throw new ClassFormatException("Invalid method signature: " + signature);
    }

    return type;
  }

  
Converts method signature to string with all class names compacted.
Params:
signature – to convert
name – of method
access – flags of method
Returns:
Human readable signature/**
   * Converts method signature to string with all class names compacted.
   *
   * @param signature to convert
   * @param name of method
   * @param access flags of method
   * @return Human readable signature
   */
  public static final String methodSignatureToString(String signature,
                                                     String name,
                                                     String access) {
    return methodSignatureToString(signature, name, access, true);
  }

  public static final String methodSignatureToString(String signature,
                                                     String name,
                                                     String access,
                                                     boolean chopit) {
    return methodSignatureToString(signature, name, access, chopit, null);
  }

  
A return type signature represents the return value from a method.
It is a series of bytes in the following grammar:
 ::=  | V
The character V indicates that the method returns no value. Otherwise, the
signature indicates the type of the return value.
An argument signature represents an argument passed to a method:
 ::= 
A method signature represents the arguments that the method expects, and
the value that it returns.
 ::= () 
::= *
This method converts such a string into a Java type declaration like
`void _main(String[])' and throws a `ClassFormatException' when the parsed
type is invalid.
Params:
signature –    Method signature
name –         Method name
access –       Method access rights
Throws:
ClassFormatException – 
Returns:
Java type declaration/**
   * A return type signature represents the return value from a method.
   * It is a series of bytes in the following grammar:
   *
   * <return_signature> ::= <field_type> | V
   *
   * The character V indicates that the method returns no value. Otherwise, the
   * signature indicates the type of the return value.
   * An argument signature represents an argument passed to a method:
   *
   * <argument_signature> ::= <field_type>
   *
   * A method signature represents the arguments that the method expects, and
   * the value that it returns.
   * <method_signature> ::= (<arguments_signature>) <return_signature>
   * <arguments_signature>::= <argument_signature>*
   *
   * This method converts such a string into a Java type declaration like
   * `void _main(String[])' and throws a `ClassFormatException' when the parsed
   * type is invalid.
   *
   * @param  signature    Method signature
   * @param  name         Method name
   * @param  access       Method access rights
   * @return Java type declaration
   * @throws  ClassFormatException
   */
  public static final String methodSignatureToString(String signature,
                                                     String name,
                                                     String access,
                                                     boolean chopit,
                                                     LocalVariableTable vars)
    throws ClassFormatException
  {
    StringBuffer buf = new StringBuffer("(");
    String       type;
    int          index;
    int          var_index = (access.indexOf("static") >= 0)? 0 : 1;

    try { // Read all declarations between for `(' and `)'
      if(signature.charAt(0) != '(')
        throw new ClassFormatException("Invalid method signature: " + signature);

      index = 1; // current string position

      while(signature.charAt(index) != ')') {
        String param_type = signatureToString(signature.substring(index), chopit);
        buf.append(param_type);

        if(vars != null) {
          LocalVariable l = vars.getLocalVariable(var_index);

          if(l != null)
            buf.append(" " + l.getName());
        } else
          buf.append(" arg" + var_index);

        if("double".equals(param_type) || "long".equals(param_type))
          var_index += 2;
        else
          var_index++;

        buf.append(", ");
        index += consumed_chars; // update position
      }

      index++; // update position

      // Read return type after `)'
      type = signatureToString(signature.substring(index), chopit);

    } catch(StringIndexOutOfBoundsException e) { // Should never occur
      throw new ClassFormatException("Invalid method signature: " + signature);
    }

    if(buf.length() > 1) // Tack off the extra ", "
      buf.setLength(buf.length() - 2);

    buf.append(")");

    return access + ((access.length() > 0)? " " : "") + // May be an empty string
      type + " " + name + buf.toString();
  }

  // Guess what this does
  private static final int pow2(int n) {
    return 1 << n;
  }

  
Replace all occurences of old in str with new.
Params:
str – String to permute
old – String to be replaced
@param
new Replacement string
Returns:
new String object/**
   * Replace all occurences of <em>old</em> in <em>str</em> with <em>new</em>.
   *
   * @param str String to permute
   * @param old String to be replaced
   * @param new Replacement string
   * @return new String object
   */
  public static final String replace(String str, String old, String new_) {
    int          index, old_index;
    StringBuffer buf = new StringBuffer();

    try {
      if((index = str.indexOf(old)) != -1) { // `old' found in str
        old_index = 0;                       // String start offset

        // While we have something to replace
        while((index = str.indexOf(old, old_index)) != -1) {
          buf.append(str.substring(old_index, index)); // append prefix
          buf.append(new_);                            // append replacement

          old_index = index + old.length(); // Skip `old'.length chars
        }

        buf.append(str.substring(old_index)); // append rest of string
        str = buf.toString();
      }
    } catch(StringIndexOutOfBoundsException e) { // Should not occur
      System.err.println(e);
    }

    return str;
  }

  
Converts signature to string with all class names compacted.
Params:
signature – to convert
Returns:
Human readable signature/**
   * Converts signature to string with all class names compacted.
   *
   * @param signature to convert
   * @return Human readable signature
   */
  public static final String signatureToString(String signature) {
    return signatureToString(signature, true);
  }

  
The field signature represents the value of an argument to a function or
the value of a variable. It is a series of bytes generated by the
following grammar:
 ::= 
      ::= ||
       ::= B|C|D|F|I|J|S|Z
     ::= L;
      ::= [
The meaning of the base types is as follows:
B byte signed byte
C char character
D double double precision IEEE float
F float single precision IEEE float
I int integer
J long long integer
L; ... an object of the given class
S short signed short
Z boolean true or false
[ ... array

This method converts this string into a Java type declaration such as
`String[]' and throws a `ClassFormatException' when the parsed type is
invalid.
Params:
signature –  Class signature
chopit – Flag that determines whether chopping is executed or not
Throws:
ClassFormatException – 
Returns:
Java type declaration/**
   * The field signature represents the value of an argument to a function or
   * the value of a variable. It is a series of bytes generated by the
   * following grammar:
   *
   * <PRE>
   * <field_signature> ::= <field_type>
   * <field_type>      ::= <base_type>|<object_type>|<array_type>
   * <base_type>       ::= B|C|D|F|I|J|S|Z
   * <object_type>     ::= L<fullclassname>;
   * <array_type>      ::= [<field_type>
   *
   * The meaning of the base types is as follows:
   * B byte signed byte
   * C char character
   * D double double precision IEEE float
   * F float single precision IEEE float
   * I int integer
   * J long long integer
   * L<fullclassname>; ... an object of the given class
   * S short signed short
   * Z boolean true or false
   * [<field sig> ... array
   * </PRE>
   *
   * This method converts this string into a Java type declaration such as
   * `String[]' and throws a `ClassFormatException' when the parsed type is
   * invalid.
   *
   * @param  signature  Class signature
   * @param chopit Flag that determines whether chopping is executed or not
   * @return Java type declaration
   * @throws ClassFormatException
   */
  public static final String signatureToString(String signature,
                                               boolean chopit)
  {
    consumed_chars = 1; // This is the default, read just one char like `B'

    try {
      switch(signature.charAt(0)) {
      case 'B' : return "byte";
      case 'C' : return "char";
      case 'D' : return "double";
      case 'F' : return "float";
      case 'I' : return "int";
      case 'J' : return "long";

      case 'L' : { // Full class name
        int    index = signature.indexOf(';'); // Look for closing `;'

        if(index < 0)
          throw new ClassFormatException("Invalid signature: " + signature);

        consumed_chars = index + 1; // "Lblabla;" `L' and `;' are removed

        return compactClassName(signature.substring(1, index), chopit);
      }

      case 'S' : return "short";
      case 'Z' : return "boolean";

      case '[' : { // Array declaration
        int          n;
        StringBuffer buf, brackets;
        String       type;
        char         ch;
        int          consumed_chars; // Shadows global var

        brackets = new StringBuffer(); // Accumulate []'s

        // Count opening brackets and look for optional size argument
        for(n=0; signature.charAt(n) == '['; n++)
          brackets.append("[]");

        consumed_chars = n; // Remember value

        // The rest of the string denotes a `<field_type>'
        type = signatureToString(signature.substring(n), chopit);

        Utility.consumed_chars += consumed_chars;
        return type + brackets.toString();
      }

      case 'V' : return "void";

      default  : throw new ClassFormatException("Invalid signature: `" +
                                            signature + "'");
      }
    } catch(StringIndexOutOfBoundsException e) { // Should never occur
      throw new ClassFormatException("Invalid signature: " + e + ":" + signature);
    }
  }

  
Parse Java type such as "char", or "java.lang.String[]" and return the
signature in byte code format, e.g. "C" or "[Ljava/lang/String;" respectively.
Params:
type – Java type
Returns:
byte code signature/** Parse Java type such as "char", or "java.lang.String[]" and return the
   * signature in byte code format, e.g. "C" or "[Ljava/lang/String;" respectively.
   *
   * @param  type Java type
   * @return byte code signature
   */
  public static String getSignature(String type) {
    StringBuffer buf        = new StringBuffer();
    char[]       chars      = type.toCharArray();
    boolean      char_found = false, delim = false;
    int          index      = -1;

  loop:
    for(int i=0; i < chars.length; i++) {
      switch(chars[i]) {
      case ' ': case '\t': case '\n': case '\r': case '\f':
        if(char_found)
          delim = true;
        break;

      case '[':
        if(!char_found)
          throw new RuntimeException("Illegal type: " + type);

        index = i;
        break loop;

      default:
        char_found = true;
        if(!delim)
          buf.append(chars[i]);
      }
    }

    int brackets = 0;

    if(index > 0)
      brackets = countBrackets(type.substring(index));

    type = buf.toString();
    buf.setLength(0);

    for(int i=0; i < brackets; i++)
      buf.append('[');

    boolean found = false;

    for(int i=Constants.T_BOOLEAN; (i <= Constants.T_VOID) && !found; i++) {
      if(Constants.TYPE_NAMES[i].equals(type)) {
        found = true;
        buf.append(Constants.SHORT_TYPE_NAMES[i]);
      }
    }

    if(!found) // Class name
      buf.append('L' + type.replace('.', '/') + ';');

    return buf.toString();
  }

  private static int countBrackets(String brackets) {
    char[]  chars = brackets.toCharArray();
    int     count = 0;
    boolean open  = false;

    for(int i=0; i<chars.length; i++) {
      switch(chars[i]) {
      case '[':
        if(open)
          throw new RuntimeException("Illegally nested brackets:" + brackets);
        open = true;
        break;

      case ']':
        if(!open)
          throw new RuntimeException("Illegally nested brackets:" + brackets);
        open = false;
        count++;
        break;

      default:
        // Don't care
      }
    }

    if(open)
      throw new RuntimeException("Illegally nested brackets:" + brackets);

    return count;
  }

  
Return type of method signature as a byte value as defined in Constants
Params:
signature – in format described above
See Also:
Constants
Returns:
type of method signature/**
   * Return type of method signature as a byte value as defined in <em>Constants</em>
   *
   * @param  signature in format described above
   * @return type of method signature
   * @see    Constants
   */
  public static final byte typeOfMethodSignature(String signature)
    throws ClassFormatException
  {
    int index;

    try {
      if(signature.charAt(0) != '(')
        throw new ClassFormatException("Invalid method signature: " + signature);

      index = signature.lastIndexOf(')') + 1;
      return typeOfSignature(signature.substring(index));
    } catch(StringIndexOutOfBoundsException e) {
      throw new ClassFormatException("Invalid method signature: " + signature);
    }
  }

  
Return type of signature as a byte value as defined in Constants
Params:
signature – in format described above
See Also:
Constants
Returns:
type of signature/**
   * Return type of signature as a byte value as defined in <em>Constants</em>
   *
   * @param  signature in format described above
   * @return type of signature
   * @see    Constants
   */
  public static final byte typeOfSignature(String signature)
    throws ClassFormatException
  {
    try {
      switch(signature.charAt(0)) {
      case 'B' : return Constants.T_BYTE;
      case 'C' : return Constants.T_CHAR;
      case 'D' : return Constants.T_DOUBLE;
      case 'F' : return Constants.T_FLOAT;
      case 'I' : return Constants.T_INT;
      case 'J' : return Constants.T_LONG;
      case 'L' : return Constants.T_REFERENCE;
      case '[' : return Constants.T_ARRAY;
      case 'V' : return Constants.T_VOID;
      case 'Z' : return Constants.T_BOOLEAN;
      case 'S' : return Constants.T_SHORT;
      default:
        throw new ClassFormatException("Invalid method signature: " + signature);
      }
    } catch(StringIndexOutOfBoundsException e) {
      throw new ClassFormatException("Invalid method signature: " + signature);
    }
  }

  
Map opcode names to opcode numbers. E.g., return Constants.ALOAD for "aload"
/** Map opcode names to opcode numbers. E.g., return Constants.ALOAD for "aload"
   */
  public static short searchOpcode(String name) {
    name = name.toLowerCase();

    for(short i=0; i < Constants.OPCODE_NAMES.length; i++)
      if(Constants.OPCODE_NAMES[i].equals(name))
        return i;

    return -1;
  }

  
Convert (signed) byte to (unsigned) short value, i.e., all negative
values become positive.
/**
   * Convert (signed) byte to (unsigned) short value, i.e., all negative
   * values become positive.
   */
  private static final short byteToShort(byte b) {
    return (b < 0)? (short)(256 + b) : (short)b;
  }

  
Convert bytes into hexidecimal string
Returns:
bytes as hexidecimal string, e.g. 00 FA 12 .../** Convert bytes into hexidecimal string
   *
   * @return bytes as hexidecimal string, e.g. 00 FA 12 ...
   */
  public static final String toHexString(byte[] bytes) {
    StringBuffer buf = new StringBuffer();

    for(int i=0; i < bytes.length; i++) {
      short  b   = byteToShort(bytes[i]);
      String hex = Integer.toString(b, 0x10);

      if(b < 0x10) // just one digit, prepend '0'
        buf.append('0');

      buf.append(hex);

      if(i < bytes.length - 1)
        buf.append(' ');
    }

    return buf.toString();
  }

  
Return a string for an integer justified left or right and filled up with
`fill' characters if necessary.
Params:
i – integer to format
length – length of desired string
left_justify – format left or right
fill – fill character
Returns:
formatted int/**
   * Return a string for an integer justified left or right and filled up with
   * `fill' characters if necessary.
   *
   * @param i integer to format
   * @param length length of desired string
   * @param left_justify format left or right
   * @param fill fill character
   * @return formatted int
   */
  public static final String format(int i, int length, boolean left_justify, char fill) {
    return fillup(Integer.toString(i), length, left_justify, fill);
  }

  
Fillup char with up to length characters with char `fill' and justify it left or right.
Params:
str – string to format
length – length of desired string
left_justify – format left or right
fill – fill character
Returns:
formatted string/**
   * Fillup char with up to length characters with char `fill' and justify it left or right.
   *
   * @param str string to format
   * @param length length of desired string
   * @param left_justify format left or right
   * @param fill fill character
   * @return formatted string
   */
  public static final String fillup(String str, int length, boolean left_justify, char fill) {
    int    len = length - str.length();
    char[] buf = new char[(len < 0)? 0 : len];

    for(int j=0; j < buf.length; j++)
      buf[j] = fill;

    if(left_justify)
      return str + new String(buf);
    else
      return new String(buf) + str;
  }

  static final boolean equals(byte[] a, byte[] b) {
    int size;

    if((size=a.length) != b.length)
      return false;

    for(int i=0; i < size; i++)
      if(a[i] != b[i])
        return false;

    return true;
  }

  public static final void printArray(PrintStream out, Object[] obj) {
    out.println(printArray(obj, true));
  }

  public static final void printArray(PrintWriter out, Object[] obj) {
    out.println(printArray(obj, true));
  }

  public static final String printArray(Object[] obj) {
    return printArray(obj, true);
  }

  public static final String printArray(Object[] obj, boolean braces) {
    return printArray(obj, braces, false);
  }

  public static final String printArray(Object[] obj, boolean braces,
                                        boolean quote) {
    if(obj == null)
      return null;

    StringBuffer buf = new StringBuffer();
    if(braces)
      buf.append('{');

    for(int i=0; i < obj.length; i++) {
      if(obj[i] != null) {
        buf.append((quote? "\"" : "") + obj[i].toString() + (quote? "\"" : ""));
      } else {
        buf.append("null");
      }

      if(i < obj.length - 1) {
        buf.append(", ");
      }
    }

    if(braces)
      buf.append('}');

    return buf.toString();
  }

  
Returns:
true, if character is one of (a, ... z, A, ... Z, 0, ... 9, _)/** @return true, if character is one of (a, ... z, A, ... Z, 0, ... 9, _)
   */
  public static boolean isJavaIdentifierPart(char ch) {
    return ((ch >= 'a') && (ch <= 'z')) ||
      ((ch >= 'A') && (ch <= 'Z')) ||
      ((ch >= '0') && (ch <= '9')) ||
      (ch == '_');
  }

  
Encode byte array it into Java identifier string, i.e., a string
that only contains the following characters: (a, ... z, A, ... Z,
0, ... 9, _, $).  The encoding algorithm itself is not too
clever: if the current byte's ASCII value already is a valid Java
identifier part, leave it as it is. Otherwise it writes the
escape character($) followed by 
 the ASCII value as a
hexadecimal string, if the value is not in the range
200..247
 
a Java identifier char not used in a lowercase
hexadecimal string, if the value is in the range
200..247

This operation inflates the original byte array by roughly 40-50%
Params:
bytes – the byte array to convert
compress – use gzip to minimize string/** Encode byte array it into Java identifier string, i.e., a string
   * that only contains the following characters: (a, ... z, A, ... Z,
   * 0, ... 9, _, $).  The encoding algorithm itself is not too
   * clever: if the current byte's ASCII value already is a valid Java
   * identifier part, leave it as it is. Otherwise it writes the
   * escape character($) followed by <p><ul><li> the ASCII value as a
   * hexadecimal string, if the value is not in the range
   * 200..247</li> <li>a Java identifier char not used in a lowercase
   * hexadecimal string, if the value is in the range
   * 200..247</li><ul></p>
   *
   * <p>This operation inflates the original byte array by roughly 40-50%</p>
   *
   * @param bytes the byte array to convert
   * @param compress use gzip to minimize string
   */
  public static String encode(byte[] bytes, boolean compress) throws IOException {
    if(compress) {
      ByteArrayOutputStream baos = new ByteArrayOutputStream();
      GZIPOutputStream      gos  = new GZIPOutputStream(baos);

      gos.write(bytes, 0, bytes.length);
      gos.close();
      baos.close();

      bytes = baos.toByteArray();
    }

    CharArrayWriter caw = new CharArrayWriter();
    JavaWriter      jw  = new JavaWriter(caw);

    for(int i=0; i < bytes.length; i++) {
      int in = bytes[i] & 0x000000ff; // Normalize to unsigned
      jw.write(in);
    }

    return caw.toString();
  }

  
Decode a string back to a byte array.
Params:
bytes – the byte array to convert
uncompress – use gzip to uncompress the stream of bytes/** Decode a string back to a byte array.
   *
   * @param bytes the byte array to convert
   * @param uncompress use gzip to uncompress the stream of bytes
   */
  public static byte[] decode(String s, boolean uncompress) throws IOException {
    char[] chars = s.toCharArray();

    CharArrayReader car = new CharArrayReader(chars);
    JavaReader      jr  = new JavaReader(car);

    ByteArrayOutputStream bos = new ByteArrayOutputStream();

    int ch;

    while((ch = jr.read()) >= 0) {
      bos.write(ch);
    }

    bos.close();
    car.close();
    jr.close();

    byte[] bytes = bos.toByteArray();

    if(uncompress) {
      GZIPInputStream gis = new GZIPInputStream(new ByteArrayInputStream(bytes));

      byte[] tmp   = new byte[bytes.length * 3]; // Rough estimate
      int    count = 0;
      int    b;

      while((b = gis.read()) >= 0)
        tmp[count++] = (byte)b;

      bytes = new byte[count];
      System.arraycopy(tmp, 0, bytes, 0, count);
    }

    return bytes;
  }

  // A-Z, g-z, _, $
  private static final int   FREE_CHARS  = 48;
  private static       int[] CHAR_MAP    = new int[FREE_CHARS];
  private static       int[] MAP_CHAR    = new int[256]; // Reverse map
  private static final char  ESCAPE_CHAR = '$';

  static {
    int j = 0, k = 0;
    for(int i='A'; i <= 'Z'; i++) {
      CHAR_MAP[j] = i;
      MAP_CHAR[i] = j;
      j++;
    }

    for(int i='g'; i <= 'z'; i++) {
      CHAR_MAP[j] = i;
      MAP_CHAR[i] = j;
      j++;
    }

    CHAR_MAP[j]   = '$';
    MAP_CHAR['$'] = j;
    j++;

    CHAR_MAP[j]   = '_';
    MAP_CHAR['_'] = j;
  }

  
Decode characters into bytes.
Used by decode()
/** Decode characters into bytes.
   * Used by <a href="Utility.html#decode(java.lang.String, boolean)">decode()</a>
   */
  private static class JavaReader extends FilterReader {
    public JavaReader(Reader in) {
      super(in);
    }

    public int read() throws IOException {
      int b = in.read();

      if(b != ESCAPE_CHAR) {
        return b;
      } else {
        int i = in.read();

        if(i < 0)
          return -1;

        if(((i >= '0') && (i <= '9')) || ((i >= 'a') && (i <= 'f'))) { // Normal escape
          int j = in.read();

          if(j < 0)
            return -1;

          char[] tmp = { (char)i, (char)j };
          int    s   = Integer.parseInt(new String(tmp), 16);

          return s;
        } else { // Special escape
          return MAP_CHAR[i];
        }
      }
    }

    public int read(char[] cbuf, int off, int len) throws IOException {
      for(int i=0; i < len; i++)
        cbuf[off + i] = (char)read();

      return len;
    }
  }

  
Encode bytes into valid java identifier characters.
Used by encode()
/** Encode bytes into valid java identifier characters.
   * Used by <a href="Utility.html#encode(byte[], boolean)">encode()</a>
   */
  private static class JavaWriter extends FilterWriter {
    public JavaWriter(Writer out) {
      super(out);
    }

    public void write(int b) throws IOException {
      if(isJavaIdentifierPart((char)b) && (b != ESCAPE_CHAR)) {
        out.write(b);
      } else {
        out.write(ESCAPE_CHAR); // Escape character

        // Special escape
        if(b >= 0 && b < FREE_CHARS) {
          out.write(CHAR_MAP[b]);
        } else { // Normal escape
          char[] tmp = Integer.toHexString(b).toCharArray();

          if(tmp.length == 1) {
            out.write('0');
            out.write(tmp[0]);
          } else {
            out.write(tmp[0]);
            out.write(tmp[1]);
          }
        }
      }
    }

    public void write(char[] cbuf, int off, int len) throws IOException {
      for(int i=0; i < len; i++)
        write(cbuf[off + i]);
    }

    public void write(String str, int off, int len) throws IOException {
      write(str.toCharArray(), off, len);
    }
  }

  
Escape all occurences of newline chars '\n', quotes \", etc.
/**
   * Escape all occurences of newline chars '\n', quotes \", etc.
   */
  public static final String convertString(String label) {
    char[]       ch  = label.toCharArray();
    StringBuffer buf = new StringBuffer();

    for(int i=0; i < ch.length; i++) {
      switch(ch[i]) {
      case '\n':
        buf.append("\\n"); break;
      case '\r':
        buf.append("\\r"); break;
      case '\"':
        buf.append("\\\""); break;
      case '\'':
        buf.append("\\'"); break;
      case '\\':
        buf.append("\\\\"); break;
      default:
        buf.append(ch[i]); break;
      }
    }

    return buf.toString();
  }
}