From 845fae3462c98b1cd28f933e03f5bc4850670737 Mon Sep 17 00:00:00 2001
From: mrmr1993 <mr_1993@hotmail.co.uk>
Date: Tue, 5 Dec 2023 22:36:18 +0000
Subject: [PATCH] Implement `srl`
---
optimism/src/mips/interpreter.rs | 26 +++++++++++++++++++++++++-
optimism/src/mips/witness.rs | 11 +++++++++++
2 files changed, 36 insertions(+), 1 deletion(-)
diff --git a/optimism/src/mips/interpreter.rs b/optimism/src/mips/interpreter.rs
index 1688798677..8f55f38c04 100644
--- a/optimism/src/mips/interpreter.rs
+++ b/optimism/src/mips/interpreter.rs
@@ -526,6 +526,19 @@ pub trait InterpreterEnv {
position: Self::Position,
) -> Self::Variable;
+ /// Return the result of shifting `x` by `by`, storing the result in `position`.
+ ///
+ /// # Safety
+ ///
+ /// There are no constraints on the returned value; callers must assert the relationship with
+ /// the source variable `x` and the shift amount `by`.
+ unsafe fn shift_right(
+ &mut self,
+ x: &Self::Variable,
+ by: &Self::Variable,
+ position: Self::Position,
+ ) -> Self::Variable;
+
/// Returns 1 if `x` is 0, or 0 otherwise, storing the result in `position`.
///
/// # Safety
@@ -665,7 +678,18 @@ pub fn interpret_rtype<Env: InterpreterEnv>(env: &mut Env, instr: RTypeInstructi
env.set_next_instruction_pointer(next_instruction_pointer + Env::constant(4u32));
return;
}
- RTypeInstruction::ShiftRightLogical => (),
+ RTypeInstruction::ShiftRightLogical => {
+ let rt = env.read_register(&rt);
+ // FIXME: Constrain this value
+ let shifted = unsafe {
+ let pos = env.alloc_scratch();
+ env.shift_right(&rt, &shamt, pos)
+ };
+ env.write_register(&rd, shifted);
+ env.set_instruction_pointer(next_instruction_pointer.clone());
+ env.set_next_instruction_pointer(next_instruction_pointer + Env::constant(4u32));
+ return;
+ }
RTypeInstruction::ShiftRightArithmetic => (),
RTypeInstruction::ShiftLeftLogicalVariable => (),
RTypeInstruction::ShiftRightLogicalVariable => (),
diff --git a/optimism/src/mips/witness.rs b/optimism/src/mips/witness.rs
index eeea858713..795a647d65 100644
--- a/optimism/src/mips/witness.rs
+++ b/optimism/src/mips/witness.rs
@@ -227,6 +227,17 @@ impl<Fp: Field> InterpreterEnv for Env<Fp> {
res
}
+ unsafe fn shift_right(
+ &mut self,
+ x: &Self::Variable,
+ by: &Self::Variable,
+ position: Self::Position,
+ ) -> Self::Variable {
+ let res = x >> by;
+ self.write_column(position, res.into());
+ res
+ }
+
unsafe fn test_zero(&mut self, x: &Self::Variable, position: Self::Position) -> Self::Variable {
let res = if *x == 0 { 1 } else { 0 };
self.write_column(position, res.into());