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package com.sun.jdo.api.persistence.enhancer.classfile;

/**
 * Environment for decoding byte codes into instructions
 */

class InsnReadEnv {

  /* The parent method environment */
  private CodeEnv codeEnv;

  /* The byte codes to be decoded */
  private byte[] byteCodes;

  /* The index into byteCodes for the next instruction to be decoded */
  private int currPc;

  /**
   * Constructor
   */
  InsnReadEnv(byte[] bytes, CodeEnv codeEnv) {
    this.byteCodes = bytes;
    this.currPc = 0;
    this.codeEnv = codeEnv;
  }

  /**
   * Return the index of the next instruction to decode
   */
  int currentPC() {
    return currPc;
  }

  /**
   * Are there more byte codes to decode?
   */
  boolean more() {
    return currPc < byteCodes.length;
  }

  /**
   * Get a single byte from the byte code stream
   */
  byte getByte() {
    if (!more())
        throw new InsnError("out of byte codes");//NOI18N

    return byteCodes[currPc++];
  }

  /**
   * Get a single unsigned byte from the byte code stream
   */
  int getUByte() {
    return getByte() & 0xff;
  }

  /**
   * Get a short from the byte code stream
   */
  int getShort() {
    byte byte1 = byteCodes[currPc++];
    byte byte2 = byteCodes[currPc++];
    return (byte1 << 8) | (byte2 & 0xff);
  }

  /**
   * Get an unsigned short from the byte code stream
   */
  int getUShort() {
    return getShort() & 0xffff;
  }

  /**
   * Get an int from the byte code stream
   */
  int getInt() {
    byte byte1 = byteCodes[currPc++];
    byte byte2 = byteCodes[currPc++];
    byte byte3 = byteCodes[currPc++];
    byte byte4 = byteCodes[currPc++];
    return (byte1 << 24) | ((byte2 & 0xff) << 16) |
	    ((byte3  & 0xff) << 8) | (byte4 & 0xff);
  }

  /**
   * Get the constant pool which applies to the method being decoded
   */
  ConstantPool pool() {
    return codeEnv.pool();
  }

  /**
   * Get the canonical InsnTarget instance for the specified
   * pc within the method.
   */
  InsnTarget getTarget(int targ) {
    return codeEnv.getTarget(targ);
  }
}