From 55af6681af783d055072adf8c49a77b2d3c103f9 Mon Sep 17 00:00:00 2001
From: Thomas Harte <thomas.harte@gmail.com>
Date: Wed, 24 Nov 2021 17:15:48 -0500
Subject: [PATCH] Avoid unnecessary `get_port_input` calls.

---
 Components/6526/Implementation/6526Implementation.hpp | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/Components/6526/Implementation/6526Implementation.hpp b/Components/6526/Implementation/6526Implementation.hpp
index f66734da2..92ecf5269 100644
--- a/Components/6526/Implementation/6526Implementation.hpp
+++ b/Components/6526/Implementation/6526Implementation.hpp
@@ -31,8 +31,10 @@ template <int port> void MOS6526<BusHandlerT, personality>::set_port_output() {
 
 template <typename BusHandlerT, Personality personality>
 template <int port> uint8_t MOS6526<BusHandlerT, personality>::get_port_input() {
-	const uint8_t input = port_handler_.get_port_input(Port(port));
-	return (input & ~data_direction_[port]) | (output_[port] & data_direction_[port]);
+	// Avoid bothering the port handler if there's no input active.
+	const uint8_t input_mask = ~data_direction_[port];
+	const uint8_t input = input_mask ? port_handler_.get_port_input(Port(port)) : 0x00;
+	return (input & input_mask) | (output_[port] & data_direction_[port]);
 }
 
 template <typename BusHandlerT, Personality personality>