From 02d4b61f6b6196de49a8a64d92f4476f3c5909a2 Mon Sep 17 00:00:00 2001
From: Craig Thomas <craig.thomas@gmail.com>
Date: Sun, 23 Jun 2024 23:09:05 -0400
Subject: [PATCH] Add store subset of register operation.

---
 chip8/cpu.py          | 38 ++++++++++++++++++++++++++++++++++----
 test/test_chip8cpu.py | 41 +++++++++++++++++++++++++++++++++++++++++
 2 files changed, 75 insertions(+), 4 deletions(-)

diff --git a/chip8/cpu.py b/chip8/cpu.py
index c48508b..daeddb2 100644
--- a/chip8/cpu.py
+++ b/chip8/cpu.py
@@ -255,10 +255,14 @@ def misc_routines(self):
         Will execute one of the routines specified in misc_routines.
         """
         operation = self.operand & 0x00FF
-        try:
-            self.misc_routine_lookup[operation]()
-        except KeyError:
-            raise UnknownOpCodeException(self.operand)
+        sub_operation = self.operand & 0x000F
+        if sub_operation == 0x2:
+            self.store_subset_regs_in_memory()
+        else:
+            try:
+                self.misc_routine_lookup[operation]()
+            except KeyError:
+                raise UnknownOpCodeException(self.operand)
 
     def clear_return(self):
         """
@@ -837,6 +841,32 @@ def set_bitplane(self):
         self.bitplane = (self.operand & 0x0F00) >> 8
         self.last_op = f"BITPLANE {self.bitplane:01X}"
 
+    def store_subset_regs_in_memory(self):
+        """
+        Fxy2 - STORSUB [I], Vx, Vy
+
+        Store a subset of registers from x to y in memory starting at index.
+        The x and y calculation is as follows:
+
+           Bits:  15-12     11-8      7-4       3-0
+                    F         x        y         2
+
+        If x is larger than y, then they will be stored in reverse order.
+        """
+        x = (self.operand & 0x0F00) >> 8
+        y = (self.operand & 0x00F0) >> 4
+        pointer = 0
+        if y >= x:
+            for z in range(x, y+1):
+                self.memory[self.index + pointer] = self.v[z]
+                pointer += 1
+        else:
+            for z in range(x, y-1, -1):
+                self.memory[self.index + pointer] = self.v[z]
+                pointer += 1
+
+        self.last_op = f"STORSUB [I], {x:01X}, {y:01X}"
+
     def move_delay_timer_into_reg(self):
         """
         Fx07 - LOAD Vx, DELAY
diff --git a/test/test_chip8cpu.py b/test/test_chip8cpu.py
index 6586767..1f0485b 100644
--- a/test/test_chip8cpu.py
+++ b/test/test_chip8cpu.py
@@ -914,6 +914,47 @@ def test_wait_for_keypress_sets_awaiting_keypress(self):
         self.assertEqual(1, self.cpu.keypress_register)
         self.assertTrue(self.cpu.awaiting_keypress)
 
+    def test_store_subset_regs_one_two(self):
+        self.cpu.v[1] = 5
+        self.cpu.v[2] = 6
+        self.cpu.index = 0x5000
+        self.cpu.operand = 0xF122
+        self.cpu.store_subset_regs_in_memory()
+        self.assertEqual(5, self.cpu.memory[0x5000])
+        self.assertEqual(6, self.cpu.memory[0x5001])
+
+    def test_store_subset_regs_one_one(self):
+        self.cpu.v[1] = 5
+        self.cpu.v[2] = 6
+        self.cpu.index = 0x5000
+        self.cpu.operand = 0xF112
+        self.cpu.store_subset_regs_in_memory()
+        self.assertEqual(5, self.cpu.memory[0x5000])
+        self.assertEqual(0, self.cpu.memory[0x5001])
+
+    def test_store_subset_regs_three_one(self):
+        self.cpu.v[1] = 5
+        self.cpu.v[2] = 6
+        self.cpu.v[3] = 7
+        self.cpu.index = 0x5000
+        self.cpu.operand = 0xF312
+        self.cpu.store_subset_regs_in_memory()
+        self.assertEqual(7, self.cpu.memory[0x5000])
+        self.assertEqual(6, self.cpu.memory[0x5001])
+        self.assertEqual(5, self.cpu.memory[0x5002])
+
+    def test_store_subset_regs_integration(self):
+        self.cpu.v[1] = 5
+        self.cpu.v[2] = 6
+        self.cpu.v[3] = 7
+        self.cpu.index = 0x5000
+        self.cpu.memory[0x0200] = 0xF3
+        self.cpu.memory[0x0201] = 0x12
+        self.cpu.execute_instruction()
+        self.assertEqual(7, self.cpu.memory[0x5000])
+        self.assertEqual(6, self.cpu.memory[0x5001])
+        self.assertEqual(5, self.cpu.memory[0x5002])
+
 # M A I N #####################################################################