From 116f9961c4ddf54eb3707f0595c585881d32ee68 Mon Sep 17 00:00:00 2001
From: Adrian Conlon <Adrian.conlon@gmail.com>
Date: Fri, 25 May 2018 22:36:10 +0100
Subject: [PATCH] Add a higher/lower nibble mask

Signed-off-by: Adrian Conlon <Adrian.conlon@gmail.com>
---
 LR35902/inc/LR35902.h |  2 +-
 Z80/src/Z80.cpp       | 12 ++++++------
 inc/Processor.h       |  3 +++
 3 files changed, 10 insertions(+), 7 deletions(-)

diff --git a/LR35902/inc/LR35902.h b/LR35902/inc/LR35902.h
index 9a70ab6..ca42282 100644
--- a/LR35902/inc/LR35902.h
+++ b/LR35902/inc/LR35902.h
@@ -31,7 +31,7 @@ namespace EightBit {
 			}
 
 			virtual register16_t& AF() final {
-				af.low &= 0xf0;
+				af.low = higherNibble(af.low);
 				return af;
 			}
 
diff --git a/Z80/src/Z80.cpp b/Z80/src/Z80.cpp
index b58603a..4dd9d37 100644
--- a/Z80/src/Z80.cpp
+++ b/Z80/src/Z80.cpp
@@ -602,7 +602,7 @@ void EightBit::Z80::rrd(uint8_t& a, uint8_t& f) {
 	++MEMPTR().word;
 	const auto memory = BUS().read();
 	BUS().write(promoteNibble(a) | highNibble(memory));
-	a = (a & 0xf0) | lowNibble(memory);
+	a = higherNibble(a) | lowerNibble(memory);
 	adjustSZPXY<Z80>(f, a);
 	clearFlag(f, NF | HC);
 }
@@ -612,7 +612,7 @@ void EightBit::Z80::rld(uint8_t& a, uint8_t& f) {
 	++MEMPTR().word;
 	const auto memory = BUS().read();
 	BUS().write(promoteNibble(memory) | lowNibble(a));
-	a = (a & 0xf0) | highNibble(memory);
+	a = higherNibble(a) | highNibble(memory);
 	adjustSZPXY<Z80>(f, a);
 	clearFlag(f, NF | HC);
 }
@@ -709,16 +709,16 @@ int EightBit::Z80::execute(const uint8_t opcode) {
 	auto& a = af.high;
 	auto& f = af.low;
 
-	auto prefixed = m_prefixCB || m_prefixED;
-	if (UNLIKELY(prefixed)) {
+	const auto prefixed = m_prefixCB || m_prefixED;
+	if (LIKELY(!prefixed)) {
+		executeOther(a, f, x, y, z, p, q);
+	} else {
 		if (m_prefixCB)
 			executeCB(a, f, x, y, z);
 		else if (m_prefixED)
 			executeED(a, f, x, y, z, p, q);
 		else
 			UNREACHABLE;
-	} else {
-		executeOther(a, f, x, y, z, p, q);
 	}
 
 	ASSUME(cycles() > 0);
diff --git a/inc/Processor.h b/inc/Processor.h
index 3b8dc53..053a249 100644
--- a/inc/Processor.h
+++ b/inc/Processor.h
@@ -61,6 +61,9 @@ namespace EightBit {
 		static int highNibble(const int value) { return value >> 4; }
 		static int lowNibble(const int value) { return value & Mask4; }
 
+		static int higherNibble(const int value) { return value & 0xf0; }
+		static int lowerNibble(const int value) { return lowNibble(value); }
+
 		static int promoteNibble(const int value) { return value << 4; }
 		static int demoteNibble(const int value) { return highNibble(value); }