core/arm7tdmi/arm/: Fix wrong calculation of op1 in DATA_PROCESSING instruction when RN==R15

The docs state: "If a register is used to specify the shift amount the PC will be 12 bytes ahead"
I probably misread that when implementing DataProcessing instructions,
and because of that added 4 bytes to (op1+8) when shift amount was specified by a rotated immediate.

Fixes #6 (and probably tons of other bugs too!)


Former-commit-id: 129f0951a6381221314c23a468c3da8b31435a30

README.md

@@ -52,7 +52,7 @@ No issues so far
 Won't boot unless binary patched to remove a loop querying the flash chip
 
 ### Dragon Ball - Legacy of Goku 2
-crashes when entering in-game menu, other than that works fine.
+~~crashes when entering in-game menu, other than that works fine.~~
 
 ## Screenshots
 

src/core/arm7tdmi/alu.rs

@@ -47,7 +47,7 @@ impl AluOpCode {
     }
 }
 
-#[derive(Debug, PartialEq, Primitive)]
+#[derive(Debug, PartialEq, Primitive, Copy, Clone)]
 pub enum BarrelShiftOpCode {
     LSL = 0,
     LSR = 1,
@@ -55,13 +55,13 @@ pub enum BarrelShiftOpCode {
     ROR = 3,
 }
 
-#[derive(Debug, PartialEq)]
+#[derive(Debug, PartialEq, Copy, Clone)]
 pub enum ShiftRegisterBy {
     ByAmount(u32),
     ByRegister(usize),
 }
 
-#[derive(Debug, PartialEq)]
+#[derive(Debug, PartialEq, Copy, Clone)]
 pub struct ShiftedRegister {
     pub reg: usize,
     pub shift_by: ShiftRegisterBy,
@@ -69,7 +69,16 @@ pub struct ShiftedRegister {
     pub added: Option<bool>,
 }
 
-#[derive(Debug, PartialEq)]
+impl ShiftedRegister {
+    pub fn is_shifted_by_reg(&self) -> bool {
+        match self.shift_by {
+            ShiftRegisterBy::ByRegister(_) => true,
+            _ => false
+        }
+    }
+}
+
+#[derive(Debug, PartialEq, Copy, Clone)]
 pub enum BarrelShifterValue {
     ImmediateValue(u32),
     RotatedImmediate(u32, u32),

src/core/arm7tdmi/arm/exec.rs

@@ -183,8 +183,8 @@ impl Core {
 
         let op2 = insn.operand2()?;
         match op2 {
-            BarrelShifterValue::ShiftedRegister(_) => {
-                if insn.rn() == REG_PC {
+            BarrelShifterValue::ShiftedRegister(shifted_reg) => {
+                if insn.rn() == REG_PC && shifted_reg.is_shifted_by_reg() {
                     op1 += 4;
                 }
             }