Nes_Cpu.cpp

// Nes_Emu 0.7.0. http://www.slack.net/~ant/nes-emu/

// TODO: remove
#if !defined (NDEBUG) && 0
	#pragma peephole on
	#pragma global_optimizer on
	#pragma optimization_level 4
	#pragma scheduling 604
	#undef BLARGG_ENABLE_OPTIMIZER
#endif

#include "Nes_Cpu.h"

#include <string.h>
#include <limits.h>
#include "blargg_endian.h"

#include "nes_cpu_io.h"

/* Copyright (C) 2003-2006 Shay Green. This module 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
module 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 Lesser General Public License for
more details. You should have received a copy of the GNU Lesser General
Public License along with this module; if not, write to the Free Software
Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA */

#include "blargg_source.h"

#ifdef BLARGG_ENABLE_OPTIMIZER
	#include BLARGG_ENABLE_OPTIMIZER
#endif

inline void Nes_Cpu::set_code_page( int i, uint8_t const* p )
{
	code_map [i] = p - (unsigned) i * page_size;
}

void Nes_Cpu::reset( void const* unmapped_page )
{
	r.status = 0;
	r.sp = 0;
	r.pc = 0;
	r.a = 0;
	r.x = 0;
	r.y = 0;
	
	error_count_ = 0;
	clock_count = 0;
	clock_limit = 0;
	irq_time_ = LONG_MAX / 2 + 1;
	end_time_ = LONG_MAX / 2 + 1;
	
	assert( page_size == 0x800 ); // assumes this
	set_code_page( 0, low_mem );
	set_code_page( 1, low_mem );
	set_code_page( 2, low_mem );
	set_code_page( 3, low_mem );
	for ( int i = 4; i < page_count + 1; i++ )
		set_code_page( i, (uint8_t*) unmapped_page );
	
	#ifndef NDEBUG
		blargg_verify_byte_order();
	#endif
}

void Nes_Cpu::map_code( nes_addr_t start, unsigned size, const void* data )
{
	// address range must begin and end on page boundaries
	require( start % page_size == 0 );
	require( size % page_size == 0 );
	require( start + size <= 0x10000 );
	
	unsigned first_page = start / page_size;
	for ( unsigned i = size / page_size; i--; )
		set_code_page( first_page + i, (uint8_t*) data + i * page_size );
}

// Note: 'addr' is evaulated more than once in the following macros, so it
// must not contain side-effects.

//static void log_read( int opcode ) { LOG_FREQ( "read", 256, opcode ); }

#define READ_LIKELY_PPU( addr ) (NES_CPU_READ_PPU( this, (addr), (clock_count) ))
#define READ( addr )            (NES_CPU_READ( this, (addr), (clock_count) ))
#define WRITE( addr, data )     {NES_CPU_WRITE( this, (addr), (data), (clock_count) );}

#define READ_LOW( addr )        (low_mem [int (addr)])
#define WRITE_LOW( addr, data ) (void) (READ_LOW( addr ) = (data))

#define READ_PROG( addr )   (code_map [(addr) >> page_bits] [addr])
#define READ_PROG16( addr ) GET_LE16( &READ_PROG( addr ) )

#define SET_SP( v )     (sp = ((v) + 1) | 0x100)
#define GET_SP()        ((sp - 1) & 0xFF)
#define PUSH( v )       ((sp = (sp - 1) | 0x100), WRITE_LOW( sp, v ))

#ifdef BLARGG_ENABLE_OPTIMIZER
	#include BLARGG_ENABLE_OPTIMIZER
#endif

int Nes_Cpu::read( nes_addr_t addr )
{
	return READ( addr );
}

void Nes_Cpu::write( nes_addr_t addr, int value )
{
	WRITE( addr, value );
}

void Nes_Cpu::set_tracecb(void (*cb)(unsigned int *data))
{
	tracecb = cb;
}

#ifndef NES_CPU_GLUE_ONLY

static const unsigned char clock_table [256] = {
//  0 1 2 3 4 5 6 7 8 9 A B C D E F
	7,6,2,8,3,3,5,5,3,2,2,2,4,4,6,6,// 0
	3,5,2,8,4,4,6,6,2,4,2,7,4,4,7,7,// 1
	6,6,2,8,3,3,5,5,4,2,2,2,4,4,6,6,// 2
	3,5,2,8,4,4,6,6,2,4,2,7,4,4,7,7,// 3
	6,6,2,8,3,3,5,5,3,2,2,2,3,4,6,6,// 4
	3,5,2,8,4,4,6,6,2,4,2,7,4,4,7,7,// 5
	6,6,2,8,3,3,5,5,4,2,2,2,5,4,6,6,// 6
	3,5,2,8,4,4,6,6,2,4,2,7,4,4,7,7,// 7
	2,6,2,6,3,3,3,3,2,2,2,2,4,4,4,4,// 8
	3,6,2,6,4,4,4,4,2,5,2,5,5,5,5,5,// 9
	2,6,2,6,3,3,3,3,2,2,2,2,4,4,4,4,// A
	3,5,2,5,4,4,4,4,2,4,2,4,4,4,4,4,// B
	2,6,2,8,3,3,5,5,2,2,2,2,4,4,6,6,// C
	3,5,2,8,4,4,6,6,2,4,2,7,4,4,7,7,// D
	2,6,2,8,3,3,5,5,2,2,2,2,4,4,6,6,// E
	3,5,2,8,4,4,6,6,2,4,2,7,4,4,7,7 // F
};

Nes_Cpu::result_t Nes_Cpu::run( nes_time_t end )
{
	set_end_time_( end );
	clock_count = 0;
	
	volatile result_t result = result_cycles;
	
#if !BLARGG_CPU_CISC
	long clock_count = this->clock_count;
	uint8_t* const low_mem = this->low_mem;
#endif

	// registers
	unsigned pc = r.pc;
	int sp;
	SET_SP( r.sp );
	int a = r.a;
	int x = r.x;
	int y = r.y;
	
	// status flags
	
	int const st_n = 0x80;
	int const st_v = 0x40;
	int const st_r = 0x20;
	int const st_b = 0x10;
	int const st_d = 0x08;
	int const st_i = 0x04;
	int const st_z = 0x02;
	int const st_c = 0x01;
	
	#define IS_NEG (nz & 0x880)
	
	#define CALC_STATUS( out ) do {             \
		out = status & (st_v | st_d | st_i);    \
		out |= (c >> 8) & st_c;                 \
		if ( IS_NEG ) out |= st_n;              \
		if ( !(nz & 0xFF) ) out |= st_z;        \
	} while ( 0 )

	#define SET_STATUS( in ) do {               \
		status = in & (st_v | st_d | st_i);     \
		c = in << 8;                            \
		nz = (in << 4) & 0x800;                 \
		nz |= ~in & st_z;                       \
	} while ( 0 )

	int status;
	int c;  // carry set if (c & 0x100) != 0
	int nz; // Z set if (nz & 0xFF) == 0, N set if (nz & 0x880) != 0
	{
		int temp = r.status;
		SET_STATUS( temp );
	}
	
	goto loop;
dec_clock_loop:
	clock_count--;
loop:
	
	assert( (unsigned) GET_SP() < 0x100 );
	assert( (unsigned) a < 0x100 );
	assert( (unsigned) x < 0x100 );
	assert( (unsigned) y < 0x100 );

	uint8_t const* page = code_map [pc >> page_bits];
	unsigned opcode = page [pc];
	pc++;
	
	if ( clock_count >= clock_limit )
		goto stop;

	if (tracecb)
	{
		unsigned int scratch[7];
		scratch[0] = a;
		scratch[1] = x;
		scratch[2] = y;
		scratch[3] = sp;
		scratch[4] = pc - 1;
		scratch[5] = status;
		scratch[6] = opcode;
		tracecb(scratch);
	}
	
	clock_count += clock_table [opcode];
	unsigned data;
	data = page [pc];
	
	switch ( opcode )
	{

// Macros

#define GET_OPERAND( addr )   page [addr]
#define GET_OPERAND16( addr ) GET_LE16( &page [addr] )

//#define GET_OPERAND( addr )   READ_PROG( addr )
//#define GET_OPERAND16( addr ) READ_PROG16( addr )

#define ADD_PAGE        (pc++, data += 0x100 * GET_OPERAND( pc ));
#define GET_ADDR()      GET_OPERAND16( pc )

#define HANDLE_PAGE_CROSSING( lsb ) clock_count += (lsb) >> 8;

#define INC_DEC_XY( reg, n ) reg = uint8_t (nz = reg + n); goto loop;

#define IND_Y(r,c) {                                            \
		int temp = READ_LOW( data ) + y;                        \
		data = temp + 0x100 * READ_LOW( uint8_t (data + 1) );   \
		if (c) HANDLE_PAGE_CROSSING( temp );                    \
		if (!(r) || (temp & 0x100))                             \
			READ( data - ( temp & 0x100 ) );                    \
	}
	
#define IND_X {                                                 \
		int temp = data + x;                                    \
		data = 0x100 * READ_LOW( uint8_t (temp + 1) ) + READ_LOW( uint8_t (temp) ); \
	}
	
#define ARITH_ADDR_MODES( op )          \
case op - 0x04: /* (ind,x) */           \
	IND_X                               \
	goto ptr##op;                       \
case op + 0x0C: /* (ind),y */           \
	IND_Y(true,true)                    \
	goto ptr##op;                       \
case op + 0x10: /* zp,X */              \
	data = uint8_t (data + x);          \
case op + 0x00: /* zp */                \
	data = READ_LOW( data );            \
	goto imm##op;                       \
case op + 0x14: /* abs,Y */             \
	data += y;                          \
	goto ind##op;                       \
case op + 0x18: /* abs,X */             \
	data += x;                          \
ind##op: {                              \
	HANDLE_PAGE_CROSSING( data );       \
	int temp = data;                    \
	ADD_PAGE                            \
	if ( temp & 0x100 )                 \
		 READ( data - 0x100 );          \
	goto ptr##op;                       \
}                                       \
case op + 0x08: /* abs */               \
	ADD_PAGE                            \
ptr##op:                                \
	data = READ( data );                \
case op + 0x04: /* imm */               \
imm##op:                                \

#define ARITH_ADDR_MODES_PTR( op )      \
case op - 0x04: /* (ind,x) */           \
	IND_X                               \
	goto imm##op;                       \
case op + 0x0C:                         \
	IND_Y(false,false)                  \
	goto imm##op;                       \
case op + 0x10: /* zp,X */              \
	data = uint8_t (data + x);          \
	goto imm##op;                       \
case op + 0x14: /* abs,Y */             \
	data += y;                          \
	goto ind##op;                       \
case op + 0x18: /* abs,X */             \
	data += x;                          \
ind##op: {                              \
	int temp = data;                    \
	ADD_PAGE                            \
	READ( data - ( temp & 0x100 ) );    \
	goto imm##op;                       \
}                                       \
case op + 0x08: /* abs */               \
	ADD_PAGE                            \
case op + 0x00: /* zp */                \
imm##op:                                \

#define BRANCH( cond )      \
{                           \
	pc++;                   \
	int offset = (BOOST::int8_t) data;  \
	int extra_clock = (pc & 0xFF) + offset; \
	if ( !(cond) ) goto dec_clock_loop; \
	pc += offset;       \
	pc = BOOST::uint16_t( pc ); \
	clock_count += (extra_clock >> 8) & 1;  \
	goto loop;          \
}

// Often-Used

	case 0xB5: // LDA zp,x
		data = uint8_t (data + x);
	case 0xA5: // LDA zp
		a = nz = READ_LOW( data );
		pc++;
		goto loop;
	
	case 0xD0: // BNE
		BRANCH( (uint8_t) nz );
	
	case 0x20: { // JSR
		int temp = pc + 1;
		pc = GET_OPERAND16( pc );
		WRITE_LOW( 0x100 | (sp - 1), temp >> 8 );
		sp = (sp - 2) | 0x100;
		WRITE_LOW( sp, temp );
		goto loop;
	}
	
	case 0x4C: // JMP abs
		pc = GET_OPERAND16( pc );
		goto loop;
	
	case 0xE8: INC_DEC_XY( x, 1 )  // INX
	
	case 0x10: // BPL
		BRANCH( !IS_NEG )
	
	ARITH_ADDR_MODES( 0xC5 ) // CMP
		nz = a - data;
		pc++;
		c = ~nz;
		nz &= 0xFF;
		goto loop;
	
	case 0x30: // BMI
		BRANCH( IS_NEG )
	
	case 0xF0: // BEQ
		BRANCH( !(uint8_t) nz );
	
	case 0x95: // STA zp,x
		data = uint8_t (data + x);
	case 0x85: // STA zp
		pc++;
		WRITE_LOW( data, a );
		goto loop;
	
	case 0xC8: INC_DEC_XY( y, 1 )  // INY

	case 0xA8: // TAY
		y = a;
	case 0x98: // TYA
		a = nz = y;
		goto loop;
	
	case 0xAD:{// LDA abs
		unsigned addr = GET_ADDR();
		pc += 2;
		a = nz = READ_LIKELY_PPU( addr );
		goto loop;
	}
	
	case 0x60: // RTS
		pc = 1 + READ_LOW( sp );
		pc += READ_LOW( 0x100 | (sp - 0xFF) ) * 0x100;
		sp = (sp - 0xFE) | 0x100;
		goto loop;

	case 0x99: // STA abs,Y
		data += y;
		goto sta_ind_common;
	
	case 0x9D: // STA abs,X
		data += x;
	sta_ind_common: {
		int temp = data;
		ADD_PAGE
		READ( data - ( temp & 0x100 ) );
		goto sta_ptr;
	}
	case 0x8D: // STA abs
		ADD_PAGE
	sta_ptr:
		pc++;
		WRITE( data, a );
		goto loop;
	
	case 0xA9: // LDA #imm
		pc++;
		a = data;
		nz = data;
		goto loop;
	
#if 0
	case 0xA1: // LDA (ind,X)
		IND_X
		goto lda_ptr;
	
	case 0xB1: // LDA (ind),Y
		IND_Y(true,true)
		goto lda_ptr;
	
	case 0xB9: // LDA abs,Y
		data += y;
		goto lda_ind_common;
	
	case 0xBD: // LDA abs,X
		data += x;
	lda_ind_common: {
		HANDLE_PAGE_CROSSING( data );
		int temp = data;
		ADD_PAGE
		if ( temp & 0x100 )
			READ( data - 0x100 );
	}
	lda_ptr:
		a = nz = READ( data );
		pc++;
		goto loop;
#else
	// optimization of most commonly used memory read instructions
	
	case 0xB9:// LDA abs,Y
		data += y;
		data -= x;
	case 0xBD:{// LDA abs,X
		pc++;
		unsigned msb = GET_OPERAND( pc );
		data += x;
		// indexed common
		pc++;
		HANDLE_PAGE_CROSSING( data );
		int temp = data;
		data += msb * 0x100;
		a = nz = READ_PROG( BOOST::uint16_t( data ) );
		if ( (unsigned) (data - 0x2000) >= 0x6000 )
			goto loop;
		if ( temp & 0x100 )
			READ( data - 0x100 );
		a = nz = READ( data );
		goto loop;
	}
	
	case 0xB1:{// LDA (ind),Y
		unsigned msb = READ_LOW( (uint8_t) (data + 1) );
		data = READ_LOW( data ) + y;
		// indexed common
		pc++;
		HANDLE_PAGE_CROSSING( data );
		int temp = data;
		data += msb * 0x100;
		a = nz = READ_PROG( BOOST::uint16_t( data ) );
		if ( (unsigned) (data - 0x2000) >= 0x6000 )
			goto loop;
		if ( temp & 0x100 )
			READ( data - 0x100 );
		a = nz = READ( data );
		goto loop;
	}
	
	case 0xA1: // LDA (ind,X)
		IND_X
		a = nz = READ( data );
		pc++;
		goto loop;
	
#endif

// Branch

	case 0x50: // BVC
		BRANCH( !(status & st_v) )
	
	case 0x70: // BVS
		BRANCH( status & st_v )
	
	case 0xB0: // BCS
		BRANCH( c & 0x100 )
	
	case 0x90: // BCC
		BRANCH( !(c & 0x100) )
	
// Load/store
	
	case 0x94: // STY zp,x
		data = uint8_t (data + x);
	case 0x84: // STY zp
		pc++;
		WRITE_LOW( data, y );
		goto loop;
	
	case 0x96: // STX zp,y
		data = uint8_t (data + y);
	case 0x86: // STX zp
		pc++;
		WRITE_LOW( data, x );
		goto loop;
	
	case 0xB6: // LDX zp,y
		data = uint8_t (data + y);
	case 0xA6: // LDX zp
		data = READ_LOW( data );
	case 0xA2: // LDX #imm
		pc++;
		x = data;
		nz = data;
		goto loop;
	
	case 0xB4: // LDY zp,x
		data = uint8_t (data + x);
	case 0xA4: // LDY zp
		data = READ_LOW( data );
	case 0xA0: // LDY #imm
		pc++;
		y = data;
		nz = data;
		goto loop;
	
	case 0x91: // STA (ind),Y
		IND_Y(false,false)
		goto sta_ptr;
	
	case 0x81: // STA (ind,X)
		IND_X
		goto sta_ptr;
	
	case 0xBC: // LDY abs,X
		data += x;
		HANDLE_PAGE_CROSSING( data );
	case 0xAC:{// LDY abs
		pc++;
		unsigned addr = data + 0x100 * GET_OPERAND( pc );
		if ( data & 0x100 )
			READ( addr - 0x100 );
		pc++;
		y = nz = READ( addr );
		goto loop;
	}
	
	case 0xBE: // LDX abs,y
		data += y;
		HANDLE_PAGE_CROSSING( data );
	case 0xAE:{// LDX abs
		pc++;
		unsigned addr = data + 0x100 * GET_OPERAND( pc );
		pc++;
		if ( data & 0x100 )
			READ( addr - 0x100 );
		x = nz = READ( addr );
		goto loop;
	}
	
	{
		int temp;
	case 0x8C: // STY abs
		temp = y;
		goto store_abs;
	
	case 0x8E: // STX abs
		temp = x;
	store_abs:
		unsigned addr = GET_ADDR();
		WRITE( addr, temp );
		pc += 2;
		goto loop;
	}

// Compare

	case 0xEC:{// CPX abs
		unsigned addr = GET_ADDR();
		pc++;
		data = READ( addr );
		goto cpx_data;
	}
	
	case 0xE4: // CPX zp
		data = READ_LOW( data );
	case 0xE0: // CPX #imm
	cpx_data:
		nz = x - data;
		pc++;
		c = ~nz;
		nz &= 0xFF;
		goto loop;
	
	case 0xCC:{// CPY abs
		unsigned addr = GET_ADDR();
		pc++;
		data = READ( addr );
		goto cpy_data;
	}
	
	case 0xC4: // CPY zp
		data = READ_LOW( data );
	case 0xC0: // CPY #imm
	cpy_data:
		nz = y - data;
		pc++;
		c = ~nz;
		nz &= 0xFF;
		goto loop;
	
// Logical

	ARITH_ADDR_MODES( 0x25 ) // AND
		nz = (a &= data);
		pc++;
		goto loop;
	
	ARITH_ADDR_MODES( 0x45 ) // EOR
		nz = (a ^= data);
		pc++;
		goto loop;
	
	ARITH_ADDR_MODES( 0x05 ) // ORA
		nz = (a |= data);
		pc++;
		goto loop;
	
	case 0x2C:{// BIT abs
		unsigned addr = GET_ADDR();
		pc += 2;
		status &= ~st_v;
		nz = READ_LIKELY_PPU( addr );
		status |= nz & st_v;
		if ( a & nz )
			goto loop;
		// result must be zero, even if N bit is set
		nz = nz << 4 & 0x800;
		goto loop;
	}
	
	case 0x24: // BIT zp
		nz = READ_LOW( data );
		pc++;
		status &= ~st_v;
		status |= nz & st_v;
		if ( a & nz )
			goto loop;
		// result must be zero, even if N bit is set
		nz = nz << 4 & 0x800;
		goto loop;
		
// Add/subtract

	ARITH_ADDR_MODES( 0xE5 ) // SBC
	case 0xEB: // unofficial equivalent
		data ^= 0xFF;
		goto adc_imm;
	
	ARITH_ADDR_MODES( 0x65 ) // ADC
	adc_imm: {
		int carry = (c >> 8) & 1;
		int ov = (a ^ 0x80) + carry + (BOOST::int8_t) data; // sign-extend
		status &= ~st_v;
		status |= (ov >> 2) & 0x40;
		c = nz = a + data + carry;
		pc++;
		a = (uint8_t) nz;
		goto loop;
	}
	
// Shift/rotate

	case 0x4A: // LSR A
	lsr_a:
		c = 0;
	case 0x6A: // ROR A
		nz = (c >> 1) & 0x80; // could use bit insert macro here
		c = a << 8;
		nz |= a >> 1;
		a = nz;
		goto loop;

	case 0x0A: // ASL A
		nz = a << 1;
		c = nz;
		a = (uint8_t) nz;
		goto loop;

	case 0x2A: { // ROL A
		nz = a << 1;
		int temp = (c >> 8) & 1;
		c = nz;
		nz |= temp;
		a = (uint8_t) nz;
		goto loop;
	}
	
	case 0x3E: // ROL abs,X
		data += x;
		goto rol_abs;
	
	case 0x1E: // ASL abs,X
		data += x;
	case 0x0E: // ASL abs
		c = 0;
	case 0x2E: // ROL abs
	rol_abs: {
		int temp = data;
		ADD_PAGE
		if ( opcode == 0x1E || opcode == 0x3E ) READ( data - ( temp & 0x100 ) );
		WRITE( data, temp = READ( data ) );
		nz = (c >> 8) & 1;
		nz |= (c = temp << 1);
    }
    rotate_common:
		pc++;
		WRITE( data, (uint8_t) nz );
		goto loop;

	case 0x7E: // ROR abs,X
		data += x;
		goto ror_abs;
	
	case 0x5E: // LSR abs,X
		data += x;
	case 0x4E: // LSR abs
		c = 0;
	case 0x6E: // ROR abs
	ror_abs: {
		int temp = data;
		ADD_PAGE
		if ( opcode == 0x5E || opcode == 0x7E ) READ( data - ( temp & 0x100 ) );
		WRITE( data, temp = READ( data ) );
		nz = ((c >> 1) & 0x80) | (temp >> 1);
		c = temp << 8;
		goto rotate_common;
	}
	
	case 0x76: // ROR zp,x
		data = uint8_t (data + x);
		goto ror_zp;
	
	case 0x56: // LSR zp,x
		data = uint8_t (data + x);
	case 0x46: // LSR zp
		c = 0;
	case 0x66: // ROR zp
	ror_zp: {
		int temp = READ_LOW( data );
		nz = ((c >> 1) & 0x80) | (temp >> 1);
		c = temp << 8;
		goto write_nz_zp;
	}
	
	case 0x36: // ROL zp,x
		data = uint8_t (data + x);
		goto rol_zp;
	
	case 0x16: // ASL zp,x
		data = uint8_t (data + x);
	case 0x06: // ASL zp
		c = 0;
	case 0x26: // ROL zp
	rol_zp:
		nz = (c >> 8) & 1;
		nz |= (c = READ_LOW( data ) << 1);
		goto write_nz_zp;
	
// Increment/decrement

	case 0xCA: INC_DEC_XY( x, -1 ) // DEX
	
	case 0x88: INC_DEC_XY( y, -1 ) // DEY
	
	case 0xF6: // INC zp,x
		data = uint8_t (data + x);
	case 0xE6: // INC zp
		nz = 1;
		goto add_nz_zp;
	
	case 0xD6: // DEC zp,x
		data = uint8_t (data + x);
	case 0xC6: // DEC zp
		nz = -1;
	add_nz_zp:
		nz += READ_LOW( data );
	write_nz_zp:
		pc++;
		WRITE_LOW( data, nz );
		goto loop;
	
	case 0xFE: { // INC abs,x
		int temp = data + x;
		data = x + GET_ADDR();
		READ( data - ( temp & 0x100 ) );
		goto inc_ptr;
	}
	
	case 0xEE: // INC abs
		data = GET_ADDR();
	inc_ptr:
		nz = 1;
		goto inc_common;
	
	case 0xDE: { // DEC abs,x
		int temp = data + x;
		data = x + GET_ADDR();
		READ( data - ( temp & 0x100 ) );
		goto dec_ptr;
	}
	
	case 0xCE: // DEC abs
		data = GET_ADDR();
	dec_ptr:
		nz = -1;
	inc_common: {
		int temp;
		WRITE( data, temp = READ( data ) );
		nz += temp;
		pc += 2;
		WRITE( data, (uint8_t) nz );
		goto loop;
	}
		
// Transfer

	case 0xAA: // TAX
		x = a;
	case 0x8A: // TXA
		a = nz = x;
		goto loop;

	case 0x9A: // TXS
		SET_SP( x ); // verified (no flag change)
		goto loop;
	
	case 0xBA: // TSX
		x = nz = GET_SP();
		goto loop;
	
// Stack
	
	case 0x48: // PHA
		PUSH( a ); // verified
		goto loop;
		
	case 0x68: // PLA
		a = nz = READ_LOW( sp );
		sp = (sp - 0xFF) | 0x100;
		goto loop;
		
	case 0x40: // RTI
		{
			int temp = READ_LOW( sp );
			pc   = READ_LOW( 0x100 | (sp - 0xFF) );
			pc  |= READ_LOW( 0x100 | (sp - 0xFE) ) * 0x100;
			sp = (sp - 0xFD) | 0x100;
			data = status;
			SET_STATUS( temp );
		}
		if ( !((data ^ status) & st_i) )
			goto loop; // I flag didn't change
	i_flag_changed:
		//dprintf( "%6d %s\n", time(), (status & st_i ? "SEI" : "CLI") );
		this->r.status = status; // update externally-visible I flag
		// update clock_limit based on modified I flag
		clock_limit = end_time_;
		if ( end_time_ <= irq_time_ )
			goto loop;
		if ( status & st_i )
			goto loop;
		clock_limit = irq_time_;
		goto loop;
	
	case 0x28:{// PLP
		int temp = READ_LOW( sp );
		sp = (sp - 0xFF) | 0x100;
		data = status;
		SET_STATUS( temp );
		if ( !((data ^ status) & st_i) )
			goto loop; // I flag didn't change
		if ( !(status & st_i) )
			goto handle_cli;
		goto handle_sei;
	}
	
	case 0x08: { // PHP
		int temp;
		CALC_STATUS( temp );
		PUSH( temp | st_b | st_r );
		goto loop;
	}
	
	case 0x6C: // JMP (ind)
		data = GET_ADDR();
		pc = READ( data );
		pc |= READ( (data & 0xFF00) | ((data + 1) & 0xFF) ) << 8;
		goto loop;
	
	case 0x00: { // BRK
		pc++;
		WRITE_LOW( 0x100 | (sp - 1), pc >> 8 );
		WRITE_LOW( 0x100 | (sp - 2), pc );
		int temp;
		CALC_STATUS( temp );
		sp = (sp - 3) | 0x100;
		WRITE_LOW( sp, temp | st_b | st_r );
		pc = GET_LE16( &code_map [0xFFFE >> page_bits] [0xFFFE] );
		status |= st_i;
		goto i_flag_changed;
	}
	
// Flags

	case 0x38: // SEC
		c = ~0;
		goto loop;
	
	case 0x18: // CLC
		c = 0;
		goto loop;
		
	case 0xB8: // CLV
		status &= ~st_v;
		goto loop;
	
	case 0xD8: // CLD
		status &= ~st_d;
		goto loop;
	
	case 0xF8: // SED
		status |= st_d;
		goto loop;
	
	case 0x58: // CLI
		if ( !(status & st_i) )
			goto loop;
		status &= ~st_i;
	handle_cli:
		//dprintf( "%6d CLI\n", time() );
		this->r.status = status; // update externally-visible I flag
		if ( clock_count < end_time_ )
		{
			assert( clock_limit == end_time_ );
			if ( end_time_ <= irq_time_ )
				goto loop; // irq is later
			if ( clock_count >= irq_time_ )
				irq_time_ = clock_count + 1; // delay IRQ until after next instruction
			clock_limit = irq_time_;
			goto loop;
		}
		// execution is stopping now, so delayed CLI must be handled by caller
		result = result_cli;
		goto end;
		
	case 0x78: // SEI
		if ( status & st_i )
			goto loop;
		status |= st_i;
	handle_sei:
		//dprintf( "%6d SEI\n", time() );
		this->r.status = status; // update externally-visible I flag
		clock_limit = end_time_;
		if ( clock_count < irq_time_ )
			goto loop;
		result = result_sei; // IRQ will occur now, even though I flag is set
		goto end;

// Unofficial
	case 0x1C: case 0x3C: case 0x5C: case 0x7C: case 0xDC: case 0xFC: { // SKW
		data += x;
		HANDLE_PAGE_CROSSING( data );
		int addr = GET_ADDR() + x;
		if ( data & 0x100 )
			READ( addr - 0x100 );
		READ( addr );
	}
	case 0x0C: // SKW
		pc++;
	case 0x74: case 0x04: case 0x14: case 0x34: case 0x44: case 0x54: case 0x64: // SKB
	case 0x80: case 0x82: case 0x89: case 0xC2: case 0xD4: case 0xE2: case 0xF4:
		pc++;
	case 0xEA: case 0x1A: case 0x3A: case 0x5A: case 0x7A: case 0xDA: case 0xFA: // NOP
		goto loop;

	ARITH_ADDR_MODES_PTR( 0xC7 ) // DCP
		WRITE( data, nz = READ( data ) );
		nz = uint8_t( nz - 1 );
		WRITE( data, nz );
		pc++;
		nz = a - nz;
		c = ~nz;
		nz &= 0xFF;
		goto loop;

	ARITH_ADDR_MODES_PTR( 0xE7 ) // ISC
		WRITE( data, nz = READ( data ) );
		nz = uint8_t( nz + 1 );
		WRITE( data, nz );
		data = nz ^ 0xFF;
		goto adc_imm;

	ARITH_ADDR_MODES_PTR( 0x27 ) { // RLA
		WRITE( data, nz = READ( data ) );
		int temp = c;
		c = nz << 1;
		nz = uint8_t( c ) | ( ( temp >> 8 ) & 0x01 );
		WRITE( data, nz );
		pc++;
		nz = a &= nz;
		goto loop;
	}

	ARITH_ADDR_MODES_PTR( 0x67 ) { // RRA
		int temp;
		WRITE( data, temp = READ( data ) );
		nz = ((c >> 1) & 0x80) | (temp >> 1);
		WRITE( data, nz );
		data = nz;
		c = temp << 8;
		goto adc_imm;
	}

	ARITH_ADDR_MODES_PTR( 0x07 ) // SLO
		WRITE( data, nz = READ( data ) );
		c = nz << 1;
		nz = uint8_t( c );
		WRITE( data, nz );
		nz = (a |= nz);
		pc++;
		goto loop;

	ARITH_ADDR_MODES_PTR( 0x47 ) // SRE
		WRITE( data, nz = READ( data ) );
		c = nz << 8;
		nz >>= 1;
		WRITE( data, nz );
		nz = a ^= nz;
		pc++;
		goto loop;

	case 0x4B: // ALR
		nz = (a &= data);
		pc++;
		goto lsr_a;

	case 0x0B: // ANC
	case 0x2B:
		nz = a &= data;
		c = a << 1;
		pc++;
		goto loop;

	case 0x6B: // ARR
		nz = a = uint8_t( ( ( data & a ) >> 1 ) | ( ( c >> 1 ) & 0x80 ) );
		c = a << 2;
		status = ( status & ~st_v ) | ( ( a ^ a << 1 ) & st_v );
		pc++;
		goto loop;

	case 0xAB: // LXA
		a = data;
		x = data;
		nz = data;
		pc++;
		goto loop;

	case 0xA3: // LAX
		IND_X
		goto lax_ptr;

	case 0xB3:
		IND_Y(true,true)
		goto lax_ptr;

	case 0xB7:
		data = uint8_t (data + y);

	case 0xA7:
		data = READ_LOW( data );
		goto lax_imm;

	case 0xBF: {
		data += y;
		HANDLE_PAGE_CROSSING( data );
		int temp = data;
		ADD_PAGE;
		if ( temp & 0x100 )
			READ( data - 0x100 );
		goto lax_ptr;
	}

	case 0xAF:
		ADD_PAGE

	lax_ptr:
		data = READ( data );
	lax_imm:
		nz = x = a = data;
		pc++;
		goto loop;

	case 0x83: // SAX
		IND_X
		goto sax_imm;

	case 0x97:
		data = uint8_t (data + y);
		goto sax_imm;

	case 0x8F:
		ADD_PAGE

	case 0x87:
	sax_imm:
		WRITE( data, a & x );
		pc++;
		goto loop;

	case 0xCB: // SBX
		data = ( a & x ) - data;
		c = ( data <= 0xFF ) ? 0x100 : 0;
		nz = x = uint8_t( data );
		pc++;
		goto loop;

	case 0x93: // SHA (ind),Y
		IND_Y(false,false)
		pc++;
		WRITE( data, uint8_t( a & x & ( ( data >> 8 ) + 1 ) ) );
		goto loop;

	case 0x9F: { // SHA abs,Y
		data += y;
		int temp = data;
		ADD_PAGE
		READ( data - ( temp & 0x100 ) );
		pc++;
		WRITE( data, uint8_t( a & x & ( ( data >> 8 ) + 1 ) ) );
		goto loop;
	}

	case 0x9E: { // SHX abs,Y
		data += y;
		int temp = data;
		ADD_PAGE
		READ( data - ( temp & 0x100 ) );
		pc++;
		if ( !( temp & 0x100 ) )
			WRITE( data, uint8_t( x & ( ( data >> 8 ) + 1 ) ) );
		goto loop;
	}

	case 0x9C: { // SHY abs,X
		data += x;
		int temp = data;
		ADD_PAGE
		READ( data - ( temp & 0x100 ) );
		pc++;
		if ( !( temp & 0x100) )
			WRITE( data, uint8_t( y & ( ( data >> 8 ) + 1 ) ) );
		goto loop;
	}

	case 0x9B: { // SHS abs,Y
		data += y;
		int temp = data;
		ADD_PAGE
		READ( data - ( temp & 0x100 ) );
		pc++;
		SET_SP( a & x );
		WRITE( data, uint8_t( a & x & ( ( data >> 8 ) + 1 ) ) );
		goto loop;
	}

	case 0xBB: { // LAS abs,Y
		data += y;
		HANDLE_PAGE_CROSSING( data );
		int temp = data;
		ADD_PAGE
		if ( temp & 0x100 )
			READ( data - 0x100 );
		pc++;
		a = GET_SP();
		x = a &= READ( data );
		SET_SP( a );
		goto loop;
	}

// Unimplemented
	
	case page_wrap_opcode: // HLT
		if ( pc > 0x10000 )
		{
			// handle wrap-around (assumes caller has put page of HLT at 0x10000)
			pc = (pc - 1) & 0xFFFF;
			clock_count -= 2;
			goto loop;
		}
		// fall through
	default:
		// skip over proper number of bytes
		static unsigned char const row [8] = { 0x95, 0x95, 0x95, 0xd5, 0x95, 0x95, 0xd5, 0xf5 };
		int len = row [opcode >> 2 & 7] >> (opcode << 1 & 6) & 3;
		if ( opcode == 0x9C )
			len = 3;
		pc += len - 1;
		error_count_++;
		goto loop;
		
		//result = result_badop; // TODO: re-enable
		goto stop;
	}
	
	// If this fails then the case above is missing an opcode
	assert( false );
	
stop:
	pc--;
end:
	
	{
		int temp;
		CALC_STATUS( temp );
		r.status = temp;
	}
	
	this->clock_count = clock_count;
	r.pc = pc;
	r.sp = GET_SP();
	r.a = a;
	r.x = x;
	r.y = y;
	irq_time_ = LONG_MAX / 2 + 1;
	
	return result;
}

#endif