Cleanups to make code nicer looking. ALU subtraction fixes.

[fpgaboy.git] / insn_alu8.v

`ifdef EXECUTE
	`INSN_ALU8: begin
		if ((opcode[2:0] == `INSN_reg_dHL) && (cycle == 0))
			`EXEC_READ(_HL);
		else begin
			`EXEC_NEWCYCLE;
			`EXEC_INC_PC;
			case (opcode[2:0])
			`INSN_reg_A:	tmp <= `_A;
			`INSN_reg_B:	tmp <= `_B;
			`INSN_reg_C:	tmp <= `_C;
			`INSN_reg_D:	tmp <= `_D;
			`INSN_reg_E:	tmp <= `_E;
			`INSN_reg_H:	tmp <= `_H;
			`INSN_reg_L:	tmp <= `_L;
			`INSN_reg_dHL:	tmp <= rdata;
			endcase
		end
	end
`endif

`ifdef WRITEBACK
	`INSN_ALU8: begin
		if ((opcode[2:0] == `INSN_reg_dHL) && (cycle == 0)) begin
			/* Sit on our asses. */
		end else begin		/* Actually do the computation! */
			case (opcode[5:3])
			`INSN_alu_ADD: begin
				`_A <= `_A + tmp;
				`_F <=	{ /* Z */ ((`_A + tmp) == 0) ? 1'b1 : 1'b0,
					  /* N */ 1'b0,
					  /* H */ (({1'b0,`_A[3:0]} + {1'b0,tmp[3:0]}) >> 4 == 1) ? 1'b1 : 1'b0,
					  /* C */ (({1'b0,`_A} + {1'b0,tmp}) >> 8 == 1) ? 1'b1 : 1'b0,
					  `_F[3:0]
					};
			end
			`INSN_alu_ADC: begin
				`_A <= `_A + tmp + {7'b0,`_F[4]};
				`_F <=	{ /* Z */ ((`_A + tmp + {7'b0,`_F[4]}) == 0) ? 1'b1 : 1'b0,
					  /* N */ 1'b0,
					  /* H */ (({1'b0,`_A[3:0]} + {1'b0,tmp[3:0]} + {4'b0,`_F[4]}) >> 4 == 1) ? 1'b1 : 1'b0,
					  /* C */ (({1'b0,`_A} + {1'b0,tmp} + {8'b0,`_F[4]}) >> 8 == 1) ? 1'b1 : 1'b0,
					  `_F[3:0]
					};
			end
			`INSN_alu_SUB: begin
				`_A <= `_A - tmp;
				`_F <=	{ /* Z */ (`_A == tmp) ? 1'b1 : 1'b0,
					  /* N */ 1'b1,
					  /* H */ (tmp[3:0] > `_A[3:0]) ? 1'b1 : 1'b0,
					  /* C */ (tmp > `_A) ? 1'b1 : 1'b0,
					  `_F[3:0]
					};
			end
			`INSN_alu_SBC: begin
				`_A <= `_A - (tmp + {7'b0,`_F[4]});
				`_F <= 	{ /* Z */ ((`_A - (tmp + {7'b0,`_F[4]})) == 0) ? 1'b1 : 1'b0,
					  /* N */ 1'b1,
					  /* H */ (({1'b0,tmp[3:0]} + {4'b0,`_F[4]}) > {1'b0,`_A[3:0]}) ? 1'b1 : 1'b0,
					  /* C */ (({1'b0,tmp} + {8'b0,`_F[4]}) > {1'b0,`_A[7:0]}) ? 1'b1 : 1'b0,
					  `_F[3:0]
					};
			end
			`INSN_alu_AND: begin
				`_A <= `_A & tmp;
				`_F <=	{ /* Z */ ((`_A & tmp) == 0) ? 1'b1 : 1'b0,
					  3'b010,
					  `_F[3:0]
					};
			end
			`INSN_alu_OR: begin
				`_A <= `_A | tmp;
				`_F <=	{ /* Z */ ((`_A | tmp) == 0) ? 1'b1 : 1'b0,
					  3'b000,
					  `_F[3:0]
					};
			end
			`INSN_alu_XOR: begin
				`_A <= `_A ^ tmp;
				`_F <=	{ /* Z */ ((`_A ^ tmp) == 0) ? 1'b1 : 1'b0,
					  3'b000,
					  `_F[3:0]
					};
			end
			`INSN_alu_CP: begin
				`_F <=	{ /* Z */ (`_A == tmp) ? 1'b1 : 1'b0,
					  /* N */ 1'b1,
					  /* H */ (tmp[3:0] > `_A[3:0]) ? 1'b1 : 1'b0,
					  /* C */ (tmp > `_A) ? 1'b1 : 1'b0,
					  `_F[3:0]
					};
			end
			default:
				$stop;
			endcase
		end
	end
`endif