/** Copyright (c) 1996-1999 Bill Venners. All Rights Reserved.** This Java source file is part of the Interactive Illustrations Web* Site, which is delivered in the applets directory of the CD-ROM* that accompanies the book "Inside the Java 2 Virtual Machine" by Bill* Venners, published by McGraw-Hill, 1999, ISBN: 0-07-135093-4. This* source file is provided for evaluation purposes only, but you can* redistribute it under certain conditions, described in the full* copyright notice below.** Full Copyright Notice:** All the web pages and Java applets delivered in the applets* directory of the CD-ROM, consisting of ".html," ".gif," ".class,"* and ".java" files, are copyrighted (c) 1996-1999 by Bill* Venners, and all rights are reserved.  This material may be copied* and placed on any commercial or non-commercial web server on any* network (including the internet) provided that the following* guidelines are followed:** a. All the web pages and Java Applets (".html," ".gif," ".class,"* and ".java" files), including the source code, that are delivered* in the applets directory of the CD-ROM that* accompanies the book must be published together on the same web* site.** b. All the web pages and Java Applets (".html," ".gif," ".class,"* and ".java" files) must be published "as is" and may not be altered* in any way.** c. All use and access to this web site must be free, and no fees* can be charged to view these materials, unless express written* permission is obtained from Bill Venners.** d. The web pages and Java Applets may not be distributed on any* media, other than a web server on a network, and may not accompany* any book or publication.** BILL VENNERS MAKES NO REPRESENTATIONS OR WARRANTIES ABOUT THE* SUITABILITY OF THE SOFTWARE, EITHER EXPRESS OR IMPLIED, INCLUDING* BUT NOT LIMITED TO THE IMPLIED WARRANTIES OF MERCHANTABILITY,* FITNESS FOR PARTICULAR PURPOSE, OR NON-INFRINGEMENT.  BILL VENNERS* SHALL NOT BE LIABLE FOR ANY DAMAGES SUFFERED BY A LICENSEE AS A* RESULT OF USING, MODIFYING OR DISTRIBUTING THIS SOFTWARE OR ITS* DERIVATIVES.*/package COM.artima.jvmsim;/*** This class represents the stack frame of the executing* method.** @author  Bill Venners*/class StackFrame {    // optop is pointer to top of operand stack. Always points    // to next location.    private int optop = 0;    private Object[] operandStack;    private Object[] localVars;    StackFrame(int maxStack, int maxLocals) {        if (maxStack > 65535 || maxLocals > 65535) {            throw new JVMSimError("maxStack = " + maxStack             + "maxLocals = " + maxLocals);        }        operandStack = new Object[maxStack];        localVars = new Object[maxLocals];    }    void resetState() {        optop = 0;        for (int i = 0; i < operandStack.length; ++i) {            operandStack[i] = null;        }        for (int i = 0; i < localVars.length; ++i) {            localVars[i] = null;        }    }    int getOptop() {        return optop;    }    Object[] getOperandStack() {        return operandStack;    }    Object[] getLocalVars() {        return localVars;    }    void setLocalDouble(int i, double theDouble) {        if (i + 1 >= localVars.length) { // use i + 1 because doubles take two            throw new JVMSimError();        }        localVars[i] = new Double(theDouble);        localVars[i + 1] = null;    }    void setLocalFloat(int i, float val) {        if (i >= localVars.length) {            throw new JVMSimError();        }        localVars[i] = new Float(val);    }    void setLocalInt(int i, int val) {        if (i >= localVars.length) {            throw new JVMSimError();        }        localVars[i] = new Integer(val);    }    void setLocalLong(int i, long theLong) {        if (i + 1 >= localVars.length) { // use i + 1 because longs take two            throw new JVMSimError();        }        localVars[i] = new Long(theLong);        localVars[i + 1] = null;    }    void setLocalObject(int i, Object val) {        if (i >= localVars.length) {            throw new JVMSimError();        }        localVars[i] = val;    }    double getLocalDouble(int i) { // untested        if (i >= localVars.length) {            throw new JVMSimError();        }        return ((Double) localVars[i]).doubleValue();    }    float getLocalFloat(int i) {        if (i >= localVars.length) {            throw new JVMSimError();        }        return ((Float) localVars[i]).floatValue();    }    int getLocalInt(int i) {        if (i >= localVars.length) {            throw new JVMSimError();        }        return ((Integer) localVars[i]).intValue();    }    long getLocalLong(int i) { // untested        if (i >= localVars.length) {            throw new JVMSimError();        }        return ((Long) localVars[i]).longValue();    }    Object getLocalObject(int i) {        if (i >= localVars.length) {            throw new JVMSimError();        }        return localVars[i];    }    void pushDouble(double theDouble) { // untested        if (optop >= operandStack.length) {            throw new JVMSimError("optop = " + optop);        }        operandStack[optop] = new Double(theDouble);        operandStack[optop + 1] = null;        optop += 2; // A double occupies two words on the stack    }    void pushFloat(float f) {        if (optop >= operandStack.length) {            throw new JVMSimError("optop = " + optop);        }        operandStack[optop] = new Float(f);        ++optop;    }    void pushInt(int val) {        if (optop >= operandStack.length) {            throw new JVMSimError("optop = " + optop);        }        operandStack[optop] = new Integer(val);        ++optop;    }    void pushLong(long theLong) { // untested        if (optop >= operandStack.length) {            throw new JVMSimError("optop = " + optop);        }        operandStack[optop] = new Long(theLong);        operandStack[optop + 1] = null;        optop += 2; // A long occupies two words on the stack    }    void pushObject(Object theObject) {        if (optop >= operandStack.length) {            throw new JVMSimError("optop = " + optop);        }        operandStack[optop] = theObject;        ++optop;    }    void pushReturnAddress(ReturnAddress retAddr) {        if (optop >= operandStack.length) {            throw new JVMSimError("optop = " + optop);        }        operandStack[optop] = retAddr;        ++optop;    }    double popDouble() {        if (optop <= 1) { // Use 1 because double occupies two slots            throw new JVMSimError();        }        optop -= 2;        double theDouble = ((Double) operandStack[optop]).doubleValue();        operandStack[optop] = null; // make available for gc        return theDouble;    }    float popFloat() {        if (optop <= 0) {            throw new JVMSimError();        }        --optop;        float f = ((Float) operandStack[optop]).floatValue();        operandStack[optop] = null; // make available for gc        return f;    }    int popInt() {        if (optop <= 0) {            throw new JVMSimError();        }        --optop;        int val = ((Integer) operandStack[optop]).intValue();        operandStack[optop] = null; // make available for gc        return val;    }    long popLong() {        if (optop <= 1) { // Use 1 because long occupies two slots            throw new JVMSimError();        }        optop -= 2;        long theLong = ((Long) operandStack[optop]).longValue();        operandStack[optop] = null; // make available for gc        return theLong;    }    Object popObject() {        if (optop <= 0) {            throw new JVMSimError();        }        --optop;        Object theObject = operandStack[optop];        operandStack[optop] = null; // make available for gc        return theObject;    }    ReturnAddress popReturnAddress() {        if (optop <= 0) {            throw new JVMSimError();        }        --optop;        ReturnAddress retAddr = (ReturnAddress) operandStack[optop];        operandStack[optop] = null; // make available for gc        return retAddr;    }	void pop() {        if (optop <= 0) {            throw new JVMSimError();        }        --optop;        operandStack[optop] = null; // make available for gc	}}