From bcc9e1c87936868886dbb24f71ab616adb20aff1 Mon Sep 17 00:00:00 2001
From: Danny Willems <be.danny.willems@gmail.com>
Date: Mon, 23 Dec 2024 21:12:41 +0100
Subject: [PATCH] WIP: no-op MIPS

---
 o1vm/src/interpreters/mips/column.rs      |  6 ++++++
 o1vm/src/interpreters/mips/interpreter.rs | 24 +++++++++++++++++++++++
 o1vm/src/interpreters/mips/witness.rs     |  8 +++++++-
 3 files changed, 37 insertions(+), 1 deletion(-)

diff --git a/o1vm/src/interpreters/mips/column.rs b/o1vm/src/interpreters/mips/column.rs
index cd895198b7..87f7fe574b 100644
--- a/o1vm/src/interpreters/mips/column.rs
+++ b/o1vm/src/interpreters/mips/column.rs
@@ -94,6 +94,12 @@ impl From<Instruction> for usize {
             IType(itype) => {
                 N_MIPS_REL_COLS + RTypeInstruction::COUNT + JTypeInstruction::COUNT + itype as usize
             }
+            Instruction::NoOp => {
+                N_MIPS_REL_COLS
+                    + RTypeInstruction::COUNT
+                    + JTypeInstruction::COUNT
+                    + ITypeInstruction::COUNT
+            }
         }
     }
 }
diff --git a/o1vm/src/interpreters/mips/interpreter.rs b/o1vm/src/interpreters/mips/interpreter.rs
index 0ea55c67ea..83a436ff02 100644
--- a/o1vm/src/interpreters/mips/interpreter.rs
+++ b/o1vm/src/interpreters/mips/interpreter.rs
@@ -31,6 +31,7 @@ pub enum Instruction {
     RType(RTypeInstruction),
     JType(JTypeInstruction),
     IType(ITypeInstruction),
+    NoOp,
 }
 
 #[derive(
@@ -153,6 +154,7 @@ impl IntoIterator for Instruction {
                 }
                 iter_contents.into_iter()
             }
+            Instruction::NoOp => vec![Instruction::NoOp].into_iter(),
         }
     }
 }
@@ -964,9 +966,31 @@ pub fn interpret_instruction<Env: InterpreterEnv>(env: &mut Env, instr: Instruct
         Instruction::RType(instr) => interpret_rtype(env, instr),
         Instruction::JType(instr) => interpret_jtype(env, instr),
         Instruction::IType(instr) => interpret_itype(env, instr),
+        Instruction::NoOp => interpret_noop(env),
     }
 }
 
+pub fn interpret_noop<Env: InterpreterEnv>(env: &mut env) {
+    let instruction_pointer = env.get_instruction_pointer();
+    let instruction = {
+        let v0 = env.read_memory(&instruction_pointer);
+        let v1 = env.read_memory(&(instruction_pointer.clone() + Env::constant(1)));
+        let v2 = env.read_memory(&(instruction_pointer.clone() + Env::constant(2)));
+        let v3 = env.read_memory(&(instruction_pointer.clone() + Env::constant(3)));
+        (v0 * Env::constant(1 << 24))
+            + (v1 * Env::constant(1 << 16))
+            + (v2 * Env::constant(1 << 8))
+            + v3
+    };
+    let opcode = {
+        let pos = env.alloc_scratch();
+        unsafe { env.bitmask(&instruction, 32, 26, pos) }
+    };
+
+    env.range_check8(&opcode, 6);
+    env.assert_zero(&opcode);
+}
+
 pub fn interpret_rtype<Env: InterpreterEnv>(env: &mut Env, instr: RTypeInstruction) {
     let instruction_pointer = env.get_instruction_pointer();
     let next_instruction_pointer = env.get_next_instruction_pointer();
diff --git a/o1vm/src/interpreters/mips/witness.rs b/o1vm/src/interpreters/mips/witness.rs
index 991b946c8d..7018b74798 100644
--- a/o1vm/src/interpreters/mips/witness.rs
+++ b/o1vm/src/interpreters/mips/witness.rs
@@ -989,7 +989,13 @@ impl<Fp: Field, PreImageOracle: PreImageOracleT> Env<Fp, PreImageOracle> {
         let opcode = {
             match instruction >> 26 {
                 0x00 => match instruction & 0x3F {
-                    0x00 => Instruction::RType(RTypeInstruction::ShiftLeftLogical),
+                    0x00 => {
+                        if instruction == 0 {
+                            Instruction::NoOp
+                        } else {
+                            Instruction::RType(RTypeInstruction::ShiftLeftLogical)
+                        }
+                    }
                     0x02 => Instruction::RType(RTypeInstruction::ShiftRightLogical),
                     0x03 => Instruction::RType(RTypeInstruction::ShiftRightArithmetic),
                     0x04 => Instruction::RType(RTypeInstruction::ShiftLeftLogicalVariable),