From befc3c90a190b3657ffb244a7926c5f641ac82be Mon Sep 17 00:00:00 2001
From: CasualPokePlayer <50538166+CasualPokePlayer@users.noreply.github.com>
Date: Wed, 29 May 2024 11:14:07 -0700
Subject: [PATCH] Fix incorrect code mapping logic

---
 source/quickerNES/core/cpu.cpp | 10 +++++-----
 source/quickerNES/core/cpu.hpp |  9 +++++++--
 2 files changed, 12 insertions(+), 7 deletions(-)

diff --git a/source/quickerNES/core/cpu.cpp b/source/quickerNES/core/cpu.cpp
index 9daf8ce..af12954 100644
--- a/source/quickerNES/core/cpu.cpp
+++ b/source/quickerNES/core/cpu.cpp
@@ -146,12 +146,12 @@ void Cpu::reset( void const* unmapped_page )
  irq_time_ = LONG_MAX / 2 + 1;
  end_time_ = LONG_MAX / 2 + 1;
 
- code_map [0] = low_mem;
- code_map [1] = low_mem - 1 * page_size;
- code_map [2] = low_mem - 2 * page_size;
- code_map [3] = low_mem - 3 * page_size;
+ set_code_page(0, low_mem);
+ set_code_page(1, low_mem);
+ set_code_page(2, low_mem);
+ set_code_page(3, low_mem);
  for ( int32_t i = 4; i < page_count + 1; i++ )
-   code_map [i] = (uint8_t*) unmapped_page;
+   set_code_page(i, (uint8_t *) unmapped_page);
 
  isCorrectExecution = true;
 }
diff --git a/source/quickerNES/core/cpu.hpp b/source/quickerNES/core/cpu.hpp
index 9eb1857..4b2a798 100644
--- a/source/quickerNES/core/cpu.hpp
+++ b/source/quickerNES/core/cpu.hpp
@@ -51,11 +51,16 @@ class Cpu
   // Clear registers, unmap memory, and map code pages to unmapped_page.
   void reset(void const *unmapped_page = 0);
 
+  inline void set_code_page(int i, uint8_t const *p)
+  {
+    code_map[i] = p - (unsigned)i * page_size;
+  }
+
   inline void map_code(nes_addr_t start, unsigned size, const void *data)
   {
     unsigned first_page = start / page_size;
-    const uint8_t *newPtr = (uint8_t *)data - start;
-    for (unsigned i = size / page_size; i--;) code_map[first_page + i] = newPtr;
+    for (unsigned i = size / page_size; i--;)
+      set_code_page(first_page + i, (uint8_t *)data + i * page_size);
   }
 
   // Access memory as the emulated CPU does.