diff --git a/src/core/common.hpp b/src/core/common.hpp
index fc68d029..6fa5f89f 100644
--- a/src/core/common.hpp
+++ b/src/core/common.hpp
@@ -14,7 +14,20 @@ using s64 = int64_t;
 using u128 = __uint128_t;
 using s128 = __int128_t;
 using m128 = __m128i;
+
 #define UINT128_MAX ((u128)0xFFFF'FFFF'FFFF'FFFF << 64) | 0xFFFF'FFFF'FFFF'FFFF
 #define UINT128_MIN 0
 #define INT128_MAX ((u128)0x7FFF'FFFF'FFFF'FFFF << 64) | 0xFFFF'FFFF'FFFF'FFFF
 #define INT128_MIN (-INT128_MAX - 1LL)
+
+template <u8 start, u8 end>
+using BitSliceType =
+std::conditional<(end - start) <= 7, u8,
+  std::conditional<(end - start) <= 15, u16,
+    std::conditional<(end - start) <= 31, u32,
+      std::conditional<(end - start) <= 63, u64,
+        std::conditional<(end - start) <= 127, u128, u128>
+      >
+    >
+  >
+>;
diff --git a/src/core/gb/Cpu.hpp b/src/core/gb/Cpu.hpp
index 0992de0b..435b2515 100644
--- a/src/core/gb/Cpu.hpp
+++ b/src/core/gb/Cpu.hpp
@@ -2,5 +2,33 @@
 #include <common.hpp>
 
 namespace natsukashii::core {
-struct Cpu {};
+template <class A, class B>
+struct RegisterPair {
+  A low;
+  B high;
+  auto operator=(const u16& rhs) {
+    low = rhs & 0xff;
+    high = rhs >> 8;
+    return *this;
+  }
+};
+
+union RegF {
+  struct {
+    unsigned z:1;
+    unsigned n:1;
+    unsigned h:1;
+    unsigned c:1;
+    unsigned:4;
+  };
+  u8 raw;
+};
+
+struct Cpu {
+private:
+  RegisterPair<u8, RegF> af;
+  RegisterPair<u8, u8> bc;
+  RegisterPair<u8, u8> de;
+  RegisterPair<u8, u8> hl;
+};
 }
diff --git a/src/core/util.hpp b/src/core/util.hpp
new file mode 100644
index 00000000..27b1902f
--- /dev/null
+++ b/src/core/util.hpp
@@ -0,0 +1,12 @@
+#pragma once
+#include <common.hpp>
+#include <type_traits>
+
+namespace natsukashii::util {
+template <u8 start, u8 end, typename T>
+BitSliceType<start, end> BitSlice(const T& num) {
+  static_assert(end - start > 127);
+  static_assert(end - start > sizeof(T));
+  return (num >> start) & ((1 << end) - 1);
+}
+}