From 37a20e125c443ac639cb4466dbb62448e07fea91 Mon Sep 17 00:00:00 2001
From: Thomas Harte <thomas.harte@gmail.com>
Date: Fri, 15 Jan 2021 22:47:52 -0500
Subject: [PATCH] Completes the M50740 decoder.

Completely untested.
---
 InstructionSets/M50740/Decoder.cpp     | 31 ++++++++++++++++---
 InstructionSets/M50740/Decoder.hpp     |  5 ++--
 InstructionSets/M50740/Instruction.hpp | 41 ++++++++++++++++++--------
 3 files changed, 58 insertions(+), 19 deletions(-)

diff --git a/InstructionSets/M50740/Decoder.cpp b/InstructionSets/M50740/Decoder.cpp
index 03be2f5e4..c43dc34e7 100644
--- a/InstructionSets/M50740/Decoder.cpp
+++ b/InstructionSets/M50740/Decoder.cpp
@@ -8,6 +8,8 @@
 
 #include "Decoder.hpp"
 
+#include <algorithm>
+
 namespace InstructionSet {
 namespace M50740 {
 
@@ -21,6 +23,7 @@ std::pair<int, InstructionSet::M50740::Instruction> Decoder::decode(const uint8_
 
 		switch(instruction) {
 			default:
+				consumed_ = 0;
 			return std::make_pair(1, Instruction());
 
 #define Map(opcode, operation, addressing_mode)	case opcode: instr_ = Instruction(Operation::operation, AddressingMode::addressing_mode); break
@@ -236,11 +239,31 @@ std::pair<int, InstructionSet::M50740::Instruction> Decoder::decode(const uint8_
 #undef Map
 		}
 
-		// TODO: can I build these into the AddressingMode constants, to avoid the switch?
-		switch(instr_.addressing_mode) {
-			default: operand_size_ = 0; break;
-		}
+		operand_size_ = size(instr_.addressing_mode);
+		phase_ = operand_size_ ? Phase::AwaitingOperand : Phase::ReadyToPost;
+		operand_bytes_ = 0;
+	}
 
+	if(phase_ == Phase::AwaitingOperand && source != end) {
+		const int outstanding_bytes = operand_size_ - operand_bytes_;
+		const int bytes_to_consume = std::min(int(end - source), outstanding_bytes);
+
+		consumed_ += bytes_to_consume;
+		source += bytes_to_consume;
+		operand_bytes_ += bytes_to_consume;
+
+		if(operand_size_ == operand_bytes_) {
+			phase_ = Phase::ReadyToPost;
+		} else {
+			return std::make_pair(-(operand_size_ - operand_bytes_), Instruction());
+		}
+	}
+
+	if(phase_ == Phase::ReadyToPost) {
+		const auto result = std::make_pair(consumed_, instr_);
+		consumed_ = 0;
+		phase_ = Phase::Instruction;
+		return result;
 	}
 
 	return std::make_pair(0, Instruction());
diff --git a/InstructionSets/M50740/Decoder.hpp b/InstructionSets/M50740/Decoder.hpp
index 68bdd3396..01b5aa1e6 100644
--- a/InstructionSets/M50740/Decoder.hpp
+++ b/InstructionSets/M50740/Decoder.hpp
@@ -24,9 +24,10 @@ class Decoder {
 	private:
 		enum class Phase {
 			Instruction,
-			AwaitingOperand
+			AwaitingOperand,
+			ReadyToPost
 		} phase_ = Phase::Instruction;
-		int operand_size_ = 0;
+		int operand_size_ = 0, operand_bytes_ = 0;
 		int consumed_ = 0;
 		Instruction instr_;
 };
diff --git a/InstructionSets/M50740/Instruction.hpp b/InstructionSets/M50740/Instruction.hpp
index 552d4e2d5..126232cd4 100644
--- a/InstructionSets/M50740/Instruction.hpp
+++ b/InstructionSets/M50740/Instruction.hpp
@@ -15,20 +15,12 @@ namespace InstructionSet {
 namespace M50740 {
 
 enum class AddressingMode {
-	Implied,
-	Accumulator,
-	Immediate,
-	Absolute,
-	AbsoluteX,
-	AbsoluteY,
-	ZeroPage,
-	ZeroPageX,
-	ZeroPageY,
-	XIndirect,
-	IndirectY,
+	Implied,			Accumulator,			Immediate,
+	Absolute,			AbsoluteX,				AbsoluteY,
+	ZeroPage,			ZeroPageX,				ZeroPageY,
+	XIndirect,			IndirectY,
 	Relative,
-	AbsoluteIndirect,
-	ZeroPageIndirect,
+	AbsoluteIndirect,	ZeroPageIndirect,
 	SpecialPage,
 	ImmediateZeroPage,
 
@@ -45,6 +37,29 @@ enum class AddressingMode {
 	Bit4ZeroPageRelative,		Bit5ZeroPageRelative,		Bit6ZeroPageRelative,		Bit7ZeroPageRelative,
 };
 
+inline int size(AddressingMode mode) {
+	// This is coupled to the AddressingMode list above; be careful!
+	constexpr int sizes[] = {
+		0, 0, 0,
+		2, 2, 2,
+		1, 1, 1,
+		1, 1,
+		1,
+		2, 1,
+		1,
+		2,
+		0,	0,	0,	0,
+		0,	0,	0,	0,
+		1,	1,	1,	1,
+		1,	1,	1,	1,
+		1,	1,	1,	1,
+		1,	1,	1,	1,
+		2,	2,	2,	2,
+		2,	2,	2,	2,
+	};
+	return sizes[int(mode)];
+}
+
 enum class Operation: uint8_t {
 	Invalid,