From a4c9724dc0f20274ef7568128c4be56de43282ac Mon Sep 17 00:00:00 2001
From: Robert Haines <rhaines@manchester.ac.uk>
Date: Sat, 24 Oct 2020 20:39:04 +0100
Subject: [PATCH] Implement INC (absolute, X).

---
 lib/mos6502/cpu_instructions.rb |  6 ++++++
 test/cpu_instructions_test.rb   | 20 ++++++++++++++++++++
 2 files changed, 26 insertions(+)

diff --git a/lib/mos6502/cpu_instructions.rb b/lib/mos6502/cpu_instructions.rb
index 81e6c13..3e3bee5 100644
--- a/lib/mos6502/cpu_instructions.rb
+++ b/lib/mos6502/cpu_instructions.rb
@@ -650,6 +650,12 @@ def instructions
         # SED
         0xf8 => lambda {
           @status.decimal_mode = true
+        },
+
+        # INC (absolute, X)
+        0xfe => lambda {
+          address = absolute(@x)
+          @memory.set(address, inc(@memory.get(address)))
         }
       }
     end
diff --git a/test/cpu_instructions_test.rb b/test/cpu_instructions_test.rb
index 5ae2baa..b3d759b 100644
--- a/test/cpu_instructions_test.rb
+++ b/test/cpu_instructions_test.rb
@@ -1551,4 +1551,24 @@ def test_0xf6
     assert(@cpu.zero?)
   end
 
+  def test_0xfe
+    @cpu.load!(
+      [
+        0xa9, 0xfe, 0xa2, 0x08, 0x9d, 0x92, 0x32,
+        0xfe, 0x92, 0x32, 0xfe, 0x92, 0x32
+      ]
+    )
+    @cpu.step
+    @cpu.step
+    @cpu.step
+    assert_equal([0xfe], @cpu.dump_memory(0x329a, 1))
+    @cpu.step
+    assert_equal([0xff], @cpu.dump_memory(0x329a, 1))
+    assert(@cpu.negative?)
+    refute(@cpu.zero?)
+    @cpu.step
+    assert_equal([0x00], @cpu.dump_memory(0x329a, 1))
+    refute(@cpu.negative?)
+    assert(@cpu.zero?)
+  end
 end