Merge pull request #1704 from TomHarte/UndefinedBehaviourRedux

Resolve minor instances of undefined behaviour.

Components/9918/Implementation/Fetch.hpp

@@ -284,10 +284,10 @@ private:
 		sprite.image[2] = colour;
 		sprite.x -= sprite.early_clock();
 
-		const AddressT graphic_location = base->sprite_generator_table_address_ & bits<11>(AddressT((name << 3) | sprite.row));
+		const AddressT graphic_location =
+			base->sprite_generator_table_address_ & bits<11>(AddressT((name << 3) | sprite.row));
 		sprite.image[0] = base->ram_[graphic_location];
-		sprite.image[1] = base->ram_[graphic_location+16];	// TODO: occasional out-of-bounds accesses here. Check
-															// uninitialised Master System.
+		sprite.image[1] = base->ram_[graphic_location | 16];
 
 		if constexpr (SpriteBuffer::test_is_filling) {
 			if(slot == ((mode == SpriteMode::Mode2) ? 7 : 3)) {

Components/SAA5050/SAA5050.cpp

@@ -9,6 +9,7 @@
 #include "SAA5050.hpp"
 
 #include <algorithm>
+#include <cassert>
 #include <cstdint>
 
 namespace {
@@ -151,7 +152,7 @@ enum ControlCode: uint8_t {
 using namespace Mullard;
 
 void SAA5050Serialiser::begin_frame(const bool is_odd) {
-	line_ = -2;
+	line_ = next_line_ = 0;
 	row_ = 0;
 	odd_frame_ = is_odd;
 
@@ -162,7 +163,7 @@ void SAA5050Serialiser::begin_frame(const bool is_odd) {
 }
 
 void SAA5050Serialiser::begin_line() {
-	line_ += 2;
+	line_ = next_line_;
 	if(line_ == 20) {
 		line_ = 0;
 		++row_;
@@ -172,6 +173,7 @@ void SAA5050Serialiser::begin_line() {
 		}
 		row_has_double_height_ = false;
 	}
+	next_line_ = line_ + 2;
 
 	output_.reset();
 	has_output_ = false;
@@ -265,6 +267,8 @@ void SAA5050Serialiser::add(const Numeric::SizedInt<7> c) {
 }
 
 void SAA5050Serialiser::load_pixels(const uint8_t c) {
+	assert(line_ >= 0 && line_ < 20);
+
 	if(flash_ && ((frame_counter_&31) > 23)) {	// Complete guess on the blink period here.
 		output_.reset();
 		return;

Components/SAA5050/SAA5050.hpp

@@ -74,7 +74,7 @@ private:
 	Output output_;
 	bool has_output_ = false;
 
-	int row_, line_;
+	int row_, line_, next_line_;
 	bool odd_frame_;
 
 	bool flash_ = false;

Machines/PCCompatible/CGA.hpp

@@ -236,7 +236,7 @@ private:
 			count += 8;
 
 			// Output pixel row prematurely if storage is exhausted.
-			if(output_state == OutputState::Pixels && pixel_pointer == pixels + DefaultAllocationSize) {
+			if(output_state == OutputState::Pixels && pixels && pixel_pointer == pixels + DefaultAllocationSize) {
 				flush_pixels();
 				count = 0;
 			}

Machines/PCCompatible/MDA.hpp

@@ -206,7 +206,7 @@ private:
 			count += 9;
 
 			// Output pixel row prematurely if storage is exhausted.
-			if(output_state == OutputState::Pixels && pixel_pointer == pixels + DefaultAllocationSize) {
+			if(output_state == OutputState::Pixels && pixels && pixel_pointer == pixels + DefaultAllocationSize) {
 				crt.output_data(count);
 				count = 0;
 

Outputs/ScanTargets/BufferingScanTarget.cpp

@@ -365,8 +365,6 @@ BufferingScanTarget::OutputArea BufferingScanTarget::get_output_area() {
 }
 
 void BufferingScanTarget::complete_output_area(const OutputArea &area) {
-	// TODO: check that this is the expected next area if in DEBUG mode.
-
 	PointerSet new_read_pointers;
 	new_read_pointers.line = uint16_t(area.end.line);
 	new_read_pointers.scan = uint16_t(area.end.scan);