/*
===========================================================================

Return to Castle Wolfenstein multiplayer GPL Source Code
Copyright (C) 1999-2010 id Software LLC, a ZeniMax Media company. 

This file is part of the Return to Castle Wolfenstein multiplayer GPL Source Code (RTCW MP Source Code).  

RTCW MP Source Code is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.

RTCW MP Source Code 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.

You should have received a copy of the GNU General Public License
along with RTCW MP Source Code.  If not, see <http://www.gnu.org/licenses/>.

In addition, the RTCW MP Source Code is also subject to certain additional terms. You should have received a copy of these additional terms immediately following the terms and conditions of the GNU General Public License which accompanied the RTCW MP Source Code.  If not, please request a copy in writing from id Software at the address below.

If you have questions concerning this license or the applicable additional terms, you may contact in writing id Software LLC, c/o ZeniMax Media Inc., Suite 120, Rockville, Maryland 20850 USA.

===========================================================================
*/

#include "vm_local.h"

#ifdef DEBUG_VM // bk001204
static char *opnames[256] = {
	"OP_UNDEF",

	"OP_IGNORE",

	"OP_BREAK",

	"OP_ENTER",
	"OP_LEAVE",
	"OP_CALL",
	"OP_PUSH",
	"OP_POP",

	"OP_CONST",

	"OP_LOCAL",

	"OP_JUMP",

	//-------------------

	"OP_EQ",
	"OP_NE",

	"OP_LTI",
	"OP_LEI",
	"OP_GTI",
	"OP_GEI",

	"OP_LTU",
	"OP_LEU",
	"OP_GTU",
	"OP_GEU",

	"OP_EQF",
	"OP_NEF",

	"OP_LTF",
	"OP_LEF",
	"OP_GTF",
	"OP_GEF",

	//-------------------

	"OP_LOAD1",
	"OP_LOAD2",
	"OP_LOAD4",
	"OP_STORE1",
	"OP_STORE2",
	"OP_STORE4",
	"OP_ARG",

	"OP_BLOCK_COPY",

	//-------------------

	"OP_SEX8",
	"OP_SEX16",

	"OP_NEGI",
	"OP_ADD",
	"OP_SUB",
	"OP_DIVI",
	"OP_DIVU",
	"OP_MODI",
	"OP_MODU",
	"OP_MULI",
	"OP_MULU",

	"OP_BAND",
	"OP_BOR",
	"OP_BXOR",
	"OP_BCOM",

	"OP_LSH",
	"OP_RSHI",
	"OP_RSHU",

	"OP_NEGF",
	"OP_ADDF",
	"OP_SUBF",
	"OP_DIVF",
	"OP_MULF",

	"OP_CVIF",
	"OP_CVFI"
};
#endif

#if defined( idppc )
	#if defined( __GNUC__ )
static inline unsigned int loadWord( void *addr ) {
	unsigned int word;

	asm ( "lwbrx %0,0,%1" : "=r" ( word ) : "r" ( addr ) );
	return word;
}
	#else
	#define loadWord( addr ) __lwbrx( addr,0 )
	#endif
#else
	#define loadWord( addr ) *( (int *)addr )
#endif

char *VM_Indent( vm_t *vm ) {
	static char *string = "                                        ";
	if ( vm->callLevel > 20 ) {
		return string;
	}
	return string + 2 * ( 20 - vm->callLevel );
}

void VM_StackTrace( vm_t *vm, int programCounter, int programStack ) {
	int count;

	count = 0;
	do {
		Com_Printf( "%s\n", VM_ValueToSymbol( vm, programCounter ) );
		programStack =  *(int *)&vm->dataBase[programStack + 4];
		programCounter = *(int *)&vm->dataBase[programStack];
	} while ( programCounter != -1 && ++count < 32 );

}


/*
====================
VM_PrepareInterpreter
====================
*/
void VM_PrepareInterpreter( vm_t *vm, vmHeader_t *header ) {
	int op;
	int pc;
	byte    *code;
	int instruction;
	int     *codeBase;

	vm->codeBase = Hunk_Alloc( vm->codeLength * 4, h_high );          // we're now int aligned
//	memcpy( vm->codeBase, (byte *)header + header->codeOffset, vm->codeLength );

	// we don't need to translate the instructions, but we still need
	// to find each instructions starting point for jumps
	pc = 0;
	instruction = 0;
	code = (byte *)header + header->codeOffset;
	codeBase = (int *)vm->codeBase;

	while ( instruction < header->instructionCount ) {
		vm->instructionPointers[ instruction ] = pc;
		instruction++;

		op = code[ pc ];
		codeBase[pc] = op;
		if ( pc > header->codeLength ) {
			Com_Error( ERR_FATAL, "VM_PrepareInterpreter: pc > header->codeLength" );
		}

		pc++;

		// these are the only opcodes that aren't a single byte
		switch ( op ) {
		case OP_ENTER:
		case OP_CONST:
		case OP_LOCAL:
		case OP_LEAVE:
		case OP_EQ:
		case OP_NE:
		case OP_LTI:
		case OP_LEI:
		case OP_GTI:
		case OP_GEI:
		case OP_LTU:
		case OP_LEU:
		case OP_GTU:
		case OP_GEU:
		case OP_EQF:
		case OP_NEF:
		case OP_LTF:
		case OP_LEF:
		case OP_GTF:
		case OP_GEF:
		case OP_BLOCK_COPY:
			codeBase[pc + 0] = loadWord( &code[pc] );
			pc += 4;
			break;
		case OP_ARG:
			codeBase[pc + 0] = code[pc];
			pc += 1;
			break;
		default:
			break;
		}

	}
	pc = 0;
	instruction = 0;
	code = (byte *)header + header->codeOffset;
	codeBase = (int *)vm->codeBase;

	while ( instruction < header->instructionCount ) {
		op = code[ pc ];
		instruction++;
		pc++;
		switch ( op ) {
		case OP_ENTER:
		case OP_CONST:
		case OP_LOCAL:
		case OP_LEAVE:
		case OP_EQ:
		case OP_NE:
		case OP_LTI:
		case OP_LEI:
		case OP_GTI:
		case OP_GEI:
		case OP_LTU:
		case OP_LEU:
		case OP_GTU:
		case OP_GEU:
		case OP_EQF:
		case OP_NEF:
		case OP_LTF:
		case OP_LEF:
		case OP_GTF:
		case OP_GEF:
		case OP_BLOCK_COPY:
			switch ( op ) {
			case OP_EQ:
			case OP_NE:
			case OP_LTI:
			case OP_LEI:
			case OP_GTI:
			case OP_GEI:
			case OP_LTU:
			case OP_LEU:
			case OP_GTU:
			case OP_GEU:
			case OP_EQF:
			case OP_NEF:
			case OP_LTF:
			case OP_LEF:
			case OP_GTF:
			case OP_GEF:
				codeBase[pc] = vm->instructionPointers[codeBase[pc]];
				break;
			default:
				break;
			}
			pc += 4;
			break;
		case OP_ARG:
			pc += 1;
			break;
		default:
			break;
		}

	}
}

/*
==============
VM_Call


Upon a system call, the stack will look like:

sp+32	parm1
sp+28	parm0
sp+24	return stack
sp+20	return address
sp+16	local1
sp+14	local0
sp+12	arg1
sp+8	arg0
sp+4	return stack
sp		return address

An interpreted function will immediately execute
an OP_ENTER instruction, which will subtract space for
locals from sp
==============
*/
#define MAX_STACK   256
#define STACK_MASK  ( MAX_STACK - 1 )
//#define	DEBUG_VM

#define DEBUGSTR va( "%s%i", VM_Indent( vm ), opStack - stack )

int VM_CallInterpreted( vm_t *vm, int *args ) {
	int stack[MAX_STACK];
	int     *opStack;
	int programCounter;
	int programStack;
	int stackOnEntry;
	byte    *image;
	int     *codeImage;
	int v1;
	int dataMask;
#ifdef DEBUG_VM
	vmSymbol_t  *profileSymbol;
#endif

	// interpret the code
	vm->currentlyInterpreting = qtrue;

	// we might be called recursively, so this might not be the very top
	programStack = stackOnEntry = vm->programStack;

#ifdef DEBUG_VM
	profileSymbol = VM_ValueToFunctionSymbol( vm, 0 );
	// uncomment this for debugging breakpoints
	vm->breakFunction = 0;
#endif
	// set up the stack frame

	image = vm->dataBase;
	codeImage = (int *)vm->codeBase;
	dataMask = vm->dataMask;

	// leave a free spot at start of stack so
	// that as long as opStack is valid, opStack-1 will
	// not corrupt anything
	opStack = stack;
	programCounter = 0;

	programStack -= 48;

	*(int *)&image[ programStack + 44] = args[9];
	*(int *)&image[ programStack + 40] = args[8];
	*(int *)&image[ programStack + 36] = args[7];
	*(int *)&image[ programStack + 32] = args[6];
	*(int *)&image[ programStack + 28] = args[5];
	*(int *)&image[ programStack + 24] = args[4];
	*(int *)&image[ programStack + 20] = args[3];
	*(int *)&image[ programStack + 16] = args[2];
	*(int *)&image[ programStack + 12] = args[1];
	*(int *)&image[ programStack + 8 ] = args[0];
	*(int *)&image[ programStack + 4 ] = 0; // return stack
	*(int *)&image[ programStack ] = -1;    // will terminate the loop on return

	vm->callLevel = 0;

	VM_Debug( 0 );

//	vm_debugLevel=2;
	// main interpreter loop, will exit when a LEAVE instruction
	// grabs the -1 program counter

#define r2 codeImage[programCounter]

	while ( 1 ) {
		int opcode, r0, r1;
//		unsigned int	r2;

nextInstruction:
		r0 = ( (int *)opStack )[0];
		r1 = ( (int *)opStack )[-1];
nextInstruction2:
		opcode = codeImage[ programCounter++ ];
#ifdef DEBUG_VM
		if ( (unsigned)programCounter > vm->codeLength ) {
			Com_Error( ERR_DROP, "VM pc out of range" );
		}

		if ( opStack < stack ) {
			Com_Error( ERR_DROP, "VM opStack underflow" );
		}
		if ( opStack >= stack + MAX_STACK ) {
			Com_Error( ERR_DROP, "VM opStack overflow" );
		}

		if ( programStack <= vm->stackBottom ) {
			Com_Error( ERR_DROP, "VM stack overflow" );
		}

		if ( programStack & 3 ) {
			Com_Error( ERR_DROP, "VM program stack misaligned" );
		}

		if ( vm_debugLevel > 1 ) {
			Com_Printf( "%s %s\n", DEBUGSTR, opnames[opcode] );
		}
		profileSymbol->profileCount++;
#endif

		switch ( opcode ) {
#ifdef DEBUG_VM
		default:
			Com_Error( ERR_DROP, "Bad VM instruction" );  // this should be scanned on load!
#endif
		case OP_BREAK:
			vm->breakCount++;
			goto nextInstruction2;
		case OP_CONST:
			opStack++;
			r1 = r0;
			r0 = *opStack = r2;

			programCounter += 4;
			goto nextInstruction2;
		case OP_LOCAL:
			opStack++;
			r1 = r0;
			r0 = *opStack = r2 + programStack;

			programCounter += 4;
			goto nextInstruction2;

		case OP_LOAD4:
#ifdef DEBUG_VM
			if ( *opStack & 3 ) {
				Com_Error( ERR_DROP, "OP_LOAD4 misaligned" );
			}
#endif
			r0 = *opStack = *(int *)&image[ r0 & dataMask ];
			goto nextInstruction2;
		case OP_LOAD2:
			r0 = *opStack = *(unsigned short *)&image[ r0 & dataMask ];
			goto nextInstruction2;
		case OP_LOAD1:
			r0 = *opStack = image[ r0 & dataMask ];
			goto nextInstruction2;

		case OP_STORE4:
			*(int *)&image[ r1 & ( dataMask & ~3 ) ] = r0;
			opStack -= 2;
			goto nextInstruction;
		case OP_STORE2:
			*(short *)&image[ r1 & ( dataMask & ~1 ) ] = r0;
			opStack -= 2;
			goto nextInstruction;
		case OP_STORE1:
			image[ r1 & dataMask ] = r0;
			opStack -= 2;
			goto nextInstruction;

		case OP_ARG:
			// single byte offset from programStack
			*(int *)&image[ codeImage[programCounter] + programStack ] = r0;
			opStack--;
			programCounter += 1;
			goto nextInstruction;

		case OP_BLOCK_COPY:
		{
			int     *src, *dest;
			int i, count, srci, desti;

			count = r2;
			// MrE: copy range check
			srci = r0 & dataMask;
			desti = r1 & dataMask;
			count = ( ( srci + count ) & dataMask ) - srci;
			count = ( ( desti + count ) & dataMask ) - desti;

			src = (int *)&image[ r0 & dataMask ];
			dest = (int *)&image[ r1 & dataMask ];
			if ( ( (int)src | (int)dest | count ) & 3 ) {
				Com_Error( ERR_DROP, "OP_BLOCK_COPY not dword aligned" );
			}
			count >>= 2;
			for ( i = count - 1 ; i >= 0 ; i-- ) {
				dest[i] = src[i];
			}
			programCounter += 4;
			opStack -= 2;
		}
			goto nextInstruction;

		case OP_CALL:
			// save current program counter
			*(int *)&image[ programStack ] = programCounter;

			// jump to the location on the stack
			programCounter = r0;
			opStack--;
			if ( programCounter < 0 ) {
				// system call
				int r;
				int temp;
#ifdef DEBUG_VM
				int stomped;

				if ( vm_debugLevel ) {
					Com_Printf( "%s---> systemcall(%i)\n", DEBUGSTR, -1 - programCounter );
				}
#endif
				// save the stack to allow recursive VM entry
				temp = vm->callLevel;
				vm->programStack = programStack - 4;
#ifdef DEBUG_VM
				stomped = *(int *)&image[ programStack + 4 ];
#endif
				*(int *)&image[ programStack + 4 ] = -1 - programCounter;

//VM_LogSyscalls( (int *)&image[ programStack + 4 ] );
				r = vm->systemCall( (int *)&image[ programStack + 4 ] );

#ifdef DEBUG_VM
				// this is just our stack frame pointer, only needed
				// for debugging
				*(int *)&image[ programStack + 4 ] = stomped;
#endif

				// save return value
				opStack++;
				*opStack = r;
				programCounter = *(int *)&image[ programStack ];
				vm->callLevel = temp;
#ifdef DEBUG_VM
				if ( vm_debugLevel ) {
					Com_Printf( "%s<--- %s\n", DEBUGSTR, VM_ValueToSymbol( vm, programCounter ) );
				}
#endif
			} else {
				programCounter = vm->instructionPointers[ programCounter ];
			}
			goto nextInstruction;

			// push and pop are only needed for discarded or bad function return values
		case OP_PUSH:
			opStack++;
			goto nextInstruction;
		case OP_POP:
			opStack--;
			goto nextInstruction;

		case OP_ENTER:
#ifdef DEBUG_VM
			profileSymbol = VM_ValueToFunctionSymbol( vm, programCounter );
#endif
			// get size of stack frame
			v1 = r2;

			programCounter += 4;
			programStack -= v1;
#ifdef DEBUG_VM
			// save old stack frame for debugging traces
			*(int *)&image[programStack + 4] = programStack + v1;
			if ( vm_debugLevel ) {
				Com_Printf( "%s---> %s\n", DEBUGSTR, VM_ValueToSymbol( vm, programCounter - 5 ) );
				if ( vm->breakFunction && programCounter - 5 == vm->breakFunction ) {
					// this is to allow setting breakpoints here in the debugger
					vm->breakCount++;
//					vm_debugLevel = 2;
//					VM_StackTrace( vm, programCounter, programStack );
				}
				vm->callLevel++;
			}
#endif
			goto nextInstruction;
		case OP_LEAVE:
			// remove our stack frame
			v1 = r2;

			programStack += v1;

			// grab the saved program counter
			programCounter = *(int *)&image[ programStack ];
#ifdef DEBUG_VM
			profileSymbol = VM_ValueToFunctionSymbol( vm, programCounter );
			if ( vm_debugLevel ) {
				vm->callLevel--;
				Com_Printf( "%s<--- %s\n", DEBUGSTR, VM_ValueToSymbol( vm, programCounter ) );
			}
#endif
			// check for leaving the VM
			if ( programCounter == -1 ) {
				goto done;
			}
			goto nextInstruction;

			/*
			===================================================================
			BRANCHES
			===================================================================
			*/

		case OP_JUMP:
			programCounter = r0;
			programCounter = vm->instructionPointers[ programCounter ];
			opStack--;
			goto nextInstruction;

		case OP_EQ:
			opStack -= 2;
			if ( r1 == r0 ) {
				programCounter = r2;    //vm->instructionPointers[r2];
				goto nextInstruction;
			} else {
				programCounter += 4;
				goto nextInstruction;
			}

		case OP_NE:
			opStack -= 2;
			if ( r1 != r0 ) {
				programCounter = r2;    //vm->instructionPointers[r2];
				goto nextInstruction;
			} else {
				programCounter += 4;
				goto nextInstruction;
			}

		case OP_LTI:
			opStack -= 2;
			if ( r1 < r0 ) {
				programCounter = r2;    //vm->instructionPointers[r2];
				goto nextInstruction;
			} else {
				programCounter += 4;
				goto nextInstruction;
			}

		case OP_LEI:
			opStack -= 2;
			if ( r1 <= r0 ) {
				programCounter = r2;    //vm->instructionPointers[r2];
				goto nextInstruction;
			} else {
				programCounter += 4;
				goto nextInstruction;
			}

		case OP_GTI:
			opStack -= 2;
			if ( r1 > r0 ) {
				programCounter = r2;    //vm->instructionPointers[r2];
				goto nextInstruction;
			} else {
				programCounter += 4;
				goto nextInstruction;
			}

		case OP_GEI:
			opStack -= 2;
			if ( r1 >= r0 ) {
				programCounter = r2;    //vm->instructionPointers[r2];
				goto nextInstruction;
			} else {
				programCounter += 4;
				goto nextInstruction;
			}

		case OP_LTU:
			opStack -= 2;
			if ( ( (unsigned)r1 ) < ( (unsigned)r0 ) ) {
				programCounter = r2;    //vm->instructionPointers[r2];
				goto nextInstruction;
			} else {
				programCounter += 4;
				goto nextInstruction;
			}

		case OP_LEU:
			opStack -= 2;
			if ( ( (unsigned)r1 ) <= ( (unsigned)r0 ) ) {
				programCounter = r2;    //vm->instructionPointers[r2];
				goto nextInstruction;
			} else {
				programCounter += 4;
				goto nextInstruction;
			}

		case OP_GTU:
			opStack -= 2;
			if ( ( (unsigned)r1 ) > ( (unsigned)r0 ) ) {
				programCounter = r2;    //vm->instructionPointers[r2];
				goto nextInstruction;
			} else {
				programCounter += 4;
				goto nextInstruction;
			}

		case OP_GEU:
			opStack -= 2;
			if ( ( (unsigned)r1 ) >= ( (unsigned)r0 ) ) {
				programCounter = r2;    //vm->instructionPointers[r2];
				goto nextInstruction;
			} else {
				programCounter += 4;
				goto nextInstruction;
			}

		case OP_EQF:
			if ( ( (float *)opStack )[-1] == *(float *)opStack ) {
				programCounter = r2;    //vm->instructionPointers[r2];
				opStack -= 2;
				goto nextInstruction;
			} else {
				programCounter += 4;
				opStack -= 2;
				goto nextInstruction;
			}

		case OP_NEF:
			if ( ( (float *)opStack )[-1] != *(float *)opStack ) {
				programCounter = r2;    //vm->instructionPointers[r2];
				opStack -= 2;
				goto nextInstruction;
			} else {
				programCounter += 4;
				opStack -= 2;
				goto nextInstruction;
			}

		case OP_LTF:
			if ( ( (float *)opStack )[-1] < *(float *)opStack ) {
				programCounter = r2;    //vm->instructionPointers[r2];
				opStack -= 2;
				goto nextInstruction;
			} else {
				programCounter += 4;
				opStack -= 2;
				goto nextInstruction;
			}

		case OP_LEF:
			if ( ( (float *)opStack )[-1] <= *(float *)opStack ) {
				programCounter = r2;    //vm->instructionPointers[r2];
				opStack -= 2;
				goto nextInstruction;
			} else {
				programCounter += 4;
				opStack -= 2;
				goto nextInstruction;
			}

		case OP_GTF:
			if ( ( (float *)opStack )[-1] > *(float *)opStack ) {
				programCounter = r2;    //vm->instructionPointers[r2];
				opStack -= 2;
				goto nextInstruction;
			} else {
				programCounter += 4;
				opStack -= 2;
				goto nextInstruction;
			}

		case OP_GEF:
			if ( ( (float *)opStack )[-1] >= *(float *)opStack ) {
				programCounter = r2;    //vm->instructionPointers[r2];
				opStack -= 2;
				goto nextInstruction;
			} else {
				programCounter += 4;
				opStack -= 2;
				goto nextInstruction;
			}


			//===================================================================

		case OP_NEGI:
			*opStack = -r0;
			goto nextInstruction;
		case OP_ADD:
			opStack[-1] = r1 + r0;
			opStack--;
			goto nextInstruction;
		case OP_SUB:
			opStack[-1] = r1 - r0;
			opStack--;
			goto nextInstruction;
		case OP_DIVI:
			opStack[-1] = r1 / r0;
			opStack--;
			goto nextInstruction;
		case OP_DIVU:
			opStack[-1] = ( (unsigned)r1 ) / ( (unsigned)r0 );
			opStack--;
			goto nextInstruction;
		case OP_MODI:
			opStack[-1] = r1 % r0;
			opStack--;
			goto nextInstruction;
		case OP_MODU:
			opStack[-1] = ( (unsigned)r1 ) % (unsigned)r0;
			opStack--;
			goto nextInstruction;
		case OP_MULI:
			opStack[-1] = r1 * r0;
			opStack--;
			goto nextInstruction;
		case OP_MULU:
			opStack[-1] = ( (unsigned)r1 ) * ( (unsigned)r0 );
			opStack--;
			goto nextInstruction;

		case OP_BAND:
			opStack[-1] = ( (unsigned)r1 ) & ( (unsigned)r0 );
			opStack--;
			goto nextInstruction;
		case OP_BOR:
			opStack[-1] = ( (unsigned)r1 ) | ( (unsigned)r0 );
			opStack--;
			goto nextInstruction;
		case OP_BXOR:
			opStack[-1] = ( (unsigned)r1 ) ^ ( (unsigned)r0 );
			opStack--;
			goto nextInstruction;
		case OP_BCOM:
			opStack[-1] = ~( (unsigned)r0 );
			goto nextInstruction;

		case OP_LSH:
			opStack[-1] = r1 << r0;
			opStack--;
			goto nextInstruction;
		case OP_RSHI:
			opStack[-1] = r1 >> r0;
			opStack--;
			goto nextInstruction;
		case OP_RSHU:
			opStack[-1] = ( (unsigned)r1 ) >> r0;
			opStack--;
			goto nextInstruction;

		case OP_NEGF:
			*(float *)opStack =  -*(float *)opStack;
			goto nextInstruction;
		case OP_ADDF:
			*( float * )( opStack - 1 ) = *( float * )( opStack - 1 ) + *(float *)opStack;
			opStack--;
			goto nextInstruction;
		case OP_SUBF:
			*( float * )( opStack - 1 ) = *( float * )( opStack - 1 ) - *(float *)opStack;
			opStack--;
			goto nextInstruction;
		case OP_DIVF:
			*( float * )( opStack - 1 ) = *( float * )( opStack - 1 ) / *(float *)opStack;
			opStack--;
			goto nextInstruction;
		case OP_MULF:
			*( float * )( opStack - 1 ) = *( float * )( opStack - 1 ) * *(float *)opStack;
			opStack--;
			goto nextInstruction;

		case OP_CVIF:
			*(float *)opStack =  (float)*opStack;
			goto nextInstruction;
		case OP_CVFI:
			*opStack = (int) *(float *)opStack;
			goto nextInstruction;
		case OP_SEX8:
			*opStack = (signed char)*opStack;
			goto nextInstruction;
		case OP_SEX16:
			*opStack = (short)*opStack;
			goto nextInstruction;
		}
	}

done:
	vm->currentlyInterpreting = qfalse;

	if ( opStack != &stack[1] ) {
		Com_Error( ERR_DROP, "Interpreter error: opStack = %i", opStack - stack );
	}

	vm->programStack = stackOnEntry;

	// return the result
	return *opStack;
}
