diff --git a/cpu/decoder.cpp b/cpu/decoder.cpp
index 4e8ac9e..a84826e 100644
--- a/cpu/decoder.cpp
+++ b/cpu/decoder.cpp
@@ -7,6 +7,16 @@ static inline u16 make_u16(u8 msb, u8 lsb)
   return (((u16)msb << 8) | (u16)lsb);
 }
 
+static inline void add16(Cpu& cpu, u16& out, u16 lhs, u16 rhs)
+{
+  u16 res11 = (lhs & 0x0FFF) + (rhs & 0x0FFF);
+  cpu.state.halfcarry = (res11 & 0x1000);
+  u32 res32 = lhs + rhs;
+  cpu.state.carry = (res32 & 0x10000);
+  cpu.state.subtract = false;
+  lhs = (u16)res32;
+}
+
 void Cpu::executeInstruction()
 {
   u16 currentpc = state.PC;
@@ -164,12 +174,7 @@ void Cpu::executeInstruction()
     }
   else if((op & 0xCF) == 0x09) // ADD HL, rr
     {
-      u16 rhs = state.reg16((op >> 4) & 0x3);
-      u16 res12 = (state.HL & 0x0FFF) + (rhs & 0x0FFF);
-      state.halfcarry = (res12 & 0x1000);
-      u32 res32 = (u32)state.HL + (u32)rhs;
-      state.carry = (res32 & 0x10000);
-      state.subtract = false;
+      add16(*this, state.HL, state.HL, state.reg16((op >> 4) & 0x3));
       mcycles = 2;
     }
   else if((op & 0xE7) == 0xC0) // RET cc
@@ -490,29 +495,15 @@ void Cpu::executeInstruction()
 
         case 0xE8: // ADD SP, e8
           {
-            u32 lhs = state.SP;
-            s32 rhs = (s8)readPC8();
-            u32 low_add = (lhs & 0x0FFF) + (rhs & 0x0FFF);
-            state.halfcarry = (low_add & 0x1000);
-            u32 res32 = lhs + rhs;
-            state.carry = (res32 & 0x10000);
-            state.SP = (u16)res32;
-            state.subtract = false;
+            add16(*this, state.SP, state.SP, (s8)readPC8());
             state.zero = false;
             mcycles = 4;
           }
           break;
         case 0xF8: // LD HL, SP + e8
           {
-            u32 lhs = state.SP;
-            s32 rhs = (s8)readPC8();
-            u32 low_add = (lhs & 0x0FFF) + (rhs & 0x0FFF);
-            state.halfcarry = (low_add & 0x1000);
-            u32 res32 = lhs + rhs;
-            state.carry = (res32 & 0x10000);
-            state.HL = (u16)res32;
+            add16(*this, state.HL, state.SP, (s32)((s8)readPC8()));
             state.zero = false;
-            state.subtract = false;
             mcycles = 3;
           }
           break;