1 files changed, 72 insertions, 0 deletions
diff --git a/src/Ryujinx.HLE/HOS/Tamper/CodeEmitters/StartEndLoop.cs b/src/Ryujinx.HLE/HOS/Tamper/CodeEmitters/StartEndLoop.cs
new file mode 100644
index 00000000..1e399b59
--- /dev/null
+++ b/src/Ryujinx.HLE/HOS/Tamper/CodeEmitters/StartEndLoop.cs
@@ -0,0 +1,72 @@
+using Ryujinx.HLE.Exceptions;
+using Ryujinx.HLE.HOS.Tamper.Operations;
+
+namespace Ryujinx.HLE.HOS.Tamper.CodeEmitters
+{
+    /// <summary>
+    /// Code type 3 allows for iterating in a loop a fixed number of times.
+    /// </summary>
+    class StartEndLoop
+    {
+        private const int StartOrEndIndex = 1;
+        private const int IterationRegisterIndex = 3;
+        private const int IterationsImmediateIndex = 8;
+
+        private const int IterationsImmediateSize = 8;
+
+        private const byte LoopBegin = 0;
+        private const byte LoopEnd = 1;
+
+        public static void Emit(byte[] instruction, CompilationContext context)
+        {
+            // 300R0000 VVVVVVVV
+            // R: Register to use as loop counter.
+            // V: Number of iterations to loop.
+
+            // 310R0000
+
+            byte mode = instruction[StartOrEndIndex];
+            byte iterationRegisterIndex = instruction[IterationRegisterIndex];
+
+            switch (mode)
+            {
+                case LoopBegin:
+                    // Just start a new compilation block and parse the instruction itself at the end.
+                    context.BlockStack.Push(new OperationBlock(instruction));
+                    return;
+                case LoopEnd:
+                    break;
+                default:
+                    throw new TamperCompilationException($"Invalid loop {mode} in Atmosphere cheat");
+            }
+
+            // Use the loop begin instruction stored in the stack.
+            instruction = context.CurrentBlock.BaseInstruction;
+            CodeType codeType = InstructionHelper.GetCodeType(instruction);
+
+            if (codeType != CodeType.StartEndLoop)
+            {
+                throw new TamperCompilationException($"Loop end does not match code type {codeType} in Atmosphere cheat");
+            }
+
+            // Validate if the register in the beginning and end are the same.
+
+            byte oldIterationRegisterIndex = instruction[IterationRegisterIndex];
+
+            if (iterationRegisterIndex != oldIterationRegisterIndex)
+            {
+                throw new TamperCompilationException($"The register used for the loop changed from {oldIterationRegisterIndex} to {iterationRegisterIndex} in Atmosphere cheat");
+            }
+
+            Register iterationRegister = context.GetRegister(iterationRegisterIndex);
+            ulong immediate = InstructionHelper.GetImmediate(instruction, IterationsImmediateIndex, IterationsImmediateSize);
+
+            // Create a loop block with the current operations and nest it in the upper
+            // block of the stack.
+
+            ForBlock block = new ForBlock(immediate, iterationRegister, context.CurrentOperations);
+            context.BlockStack.Pop();
+            context.CurrentOperations.Add(block);
+        }
+    }
+}