#pragma once

/*
 * Follows the general 8-bit opcodes:
 *
 * See http://www.c-jump.com/CIS77/CPU/IsaDesign/lecture.html
 *
 * iiirrmmm (general two operand opcode format)
 * 
 * iii instruction/opcode group
 * rr  register operand
 * mmm second operand
 *
 * iii  = 000 special commands (zero or one operand)
 *      = 001 or
 *      = 010 and
 *      = 011 cmp
 *      = 100 sub
 *      = 101 add
 *      = 11x mov
 *      = 110 mov (load)
 *      = 111 mov (store)
 *
 * rr  = 00 AX
 *       01 BX
 *       10 CX
 *       11 DX
 *
 * mmm = 000 AX
 *       001 BX
 *       010 CX
 *       011 DX
 *       100 illegal
 *       101 illegal
 *       110 direct memory
 *       111 constant
 *
 * 000iimmm (general one operand opcode format)
 * 
 * ii instruction/opcode group
 * mmm operand
 *
 * ii   = 00 (special commands) zero-operand commands
 *      = 01 jump instructions
 *      = 10 not
 *      = 11 stack (push and pop registers to/from stack)
 *
 * for jmp:
 *
 * mmm = 000 je (Z set)
 *       001 jne (Z not set)
 *       010 jb (C set)
 *       011 jbe (C set or Z set)
 *       100 ja (C not set and Z not set)
 *       101 jae (C not set)
 *       110 jmp (unconditional)
 *       111 jsr (subroutine call, push PC on stack)
 *
 * for not:
 *
 * mmm = 000 AX
 *       001 BX
 *       010 CX
 *       011 DX
 *       100 illegal
 *       101 illegal
 *       110 illegal
 *       111 illegal
 * 
 * for push/pop
 * 
 * mmm = 000 push AX
 *       001 push BX
 *       010 push CX
 *       011 push DX
 *       100 pop AX
 *       101 pop BX
 *       110 pop CX
 *       111 pop DX
 *
 * 00000iii zero-operand instructions
 * 
 * iii instruction/opcode group
 * 
 * iii = 000 illegal
 *     = 001 nop
 *     = 010 hlt
 *     = 011 ret (return from subroute call, restore PC from stack)
 *     = 100 illegal
 *     = 101 illegal
 *     = 110 illegal
 *     = 111 illegal
 *
 */
typedef enum Opcode {
	OPCODE_GROUP_ZERO_OPERANDS = (unsigned char)0x07,
	OPCODE_GROUP_ONE_OPERAND = (unsigned char)0x18,
	OPCODE_GROUP_TWO_OPERANDS = (unsigned char)0xe0,

	OPCODE_MOV_MASK = (unsigned char)0xc0,
	OPCODE_MOV_LD = (unsigned char)0xc0,
	OPCODE_MOV_ST = (unsigned char)0xe8,

	OPCODE_DST_MASK = (unsigned char)0x18,
	OPCODE_DST_AX_REG = (unsigned char)0x00,
	OPCODE_DST_BX_REG = (unsigned char)0x08,
	OPCODE_DST_CX_REG = (unsigned char)0x10,
	OPCODE_DST_DX_REG = (unsigned char)0x18,

	OPCODE_SRC_MASK = (unsigned char)0x07,
	OPCODE_SRC_AX_REG = (unsigned char)0x00,
	OPCODE_SRC_BX_REG = (unsigned char)0x01,
	OPCODE_SRC_CX_REG = (unsigned char)0x02,
	OPCODE_SRC_DX_REG = (unsigned char)0x03,
	OPCODE_SRC_CONST = (unsigned char)0x07,
	OPCODE_SRC_MEMORY = (unsigned char)0x06,

	OPCODE_OR = (unsigned char)0x20,
	OPCODE_AND = (unsigned char)0x40,
	OPCODE_CMP = (unsigned char)0x60,
	OPCODE_SUB = (unsigned char)0x80,
	OPCODE_ADD = (unsigned char)0xa0,

	OPCODE_JMP = (unsigned char)0x08,
	
	OPCODE_JMP_MASK = (unsigned char)0x07,
	OPCODE_JMP_JE = (unsigned char)0x00,
	OPCODE_JMP_JNE = (unsigned char)0x01,
	OPCODE_JMP_JB = (unsigned char)0x02,
	OPCODE_JMP_JBE = (unsigned char)0x03,
	OPCODE_JMP_JA = (unsigned char)0x04,
	OPCODE_JMP_JAE = (unsigned char)0x05,
	OPCODE_JMP_JMP = (unsigned char)0x06,
	OPCODE_JMP_JSR = (unsigned char)0x07,
	
	OPCODE_NOT = (unsigned char)0x10,
	
	OPCODE_STACK = (unsigned char)0x18,
	OPCODE_STACK_OPERAND_MASK = (unsigned char)0x3,
	OPCODE_STACK_PUSH = (unsigned char)0x0,
	OPCODE_STACK_POP = (unsigned char)0x4,

	OPCODE_ZERO_OPS_MASK = (unsigned char)0xf8,

	OPCODE_NOP = (unsigned char)0x01,
	OPCODE_HLT = (unsigned char)0x02,
	OPCODE_RET = (unsigned char)0x03
} Opcode;