From ebcd6bb5bfd09720c9a6c28ddae34ea4f593d45b Mon Sep 17 00:00:00 2001
From: Danny Willems <be.danny.willems@gmail.com>
Date: Wed, 20 Nov 2024 16:22:33 +0100
Subject: [PATCH 1/2] o1vm/riscv32: implement mul_lo_signed

---
 o1vm/src/interpreters/riscv32im/constraints.rs |  9 +++++++++
 o1vm/src/interpreters/riscv32im/interpreter.rs | 14 ++++++++++++++
 o1vm/src/interpreters/riscv32im/witness.rs     | 15 +++++++++++++++
 3 files changed, 38 insertions(+)

diff --git a/o1vm/src/interpreters/riscv32im/constraints.rs b/o1vm/src/interpreters/riscv32im/constraints.rs
index 11dee8a230..82b9cd5105 100644
--- a/o1vm/src/interpreters/riscv32im/constraints.rs
+++ b/o1vm/src/interpreters/riscv32im/constraints.rs
@@ -336,6 +336,15 @@ impl<Fp: Field> InterpreterEnv for Env<Fp> {
         self.variable(position)
     }
 
+    unsafe fn mul_lo_signed(
+        &mut self,
+        _x: &Self::Variable,
+        _y: &Self::Variable,
+        position: Self::Position,
+    ) -> Self::Variable {
+        self.variable(position)
+    }
+
     unsafe fn mul_hi_lo(
         &mut self,
         _x: &Self::Variable,
diff --git a/o1vm/src/interpreters/riscv32im/interpreter.rs b/o1vm/src/interpreters/riscv32im/interpreter.rs
index 1e41918b20..2cd83827a1 100644
--- a/o1vm/src/interpreters/riscv32im/interpreter.rs
+++ b/o1vm/src/interpreters/riscv32im/interpreter.rs
@@ -1215,6 +1215,20 @@ pub trait InterpreterEnv {
         position: Self::Position,
     ) -> Self::Variable;
 
+    /// Returns `(x * y) & ((1 << 32) - 1))`, storing the results in `position`
+    ///
+    /// # Safety
+    ///
+    /// There are no constraints on the returned values; callers must manually add constraints to
+    /// ensure that the pair of returned values correspond to the given values `x` and `y`, and
+    /// that they fall within the desired range.
+    unsafe fn mul_lo_signed(
+        &mut self,
+        x: &Self::Variable,
+        y: &Self::Variable,
+        position: Self::Position,
+    ) -> Self::Variable;
+
     /// Returns `((x * y) >> 32, (x * y) & ((1 << 32) - 1))`, storing the results in `position_hi`
     /// and `position_lo` respectively.
     ///
diff --git a/o1vm/src/interpreters/riscv32im/witness.rs b/o1vm/src/interpreters/riscv32im/witness.rs
index 0418852ae9..658048bf99 100644
--- a/o1vm/src/interpreters/riscv32im/witness.rs
+++ b/o1vm/src/interpreters/riscv32im/witness.rs
@@ -456,6 +456,21 @@ impl<Fp: Field> InterpreterEnv for Env<Fp> {
         res
     }
 
+    unsafe fn mul_lo_signed(
+        &mut self,
+        x: &Self::Variable,
+        y: &Self::Variable,
+        position: Self::Position,
+    ) -> Self::Variable {
+        let x: u32 = (*x).try_into().unwrap();
+        let y: u32 = (*y).try_into().unwrap();
+        let res = (((x as i32) as i64) * ((y as i32) as i64)) as u64;
+        let res = (res & ((1 << 32) - 1)) as u32;
+        let res = res as u64;
+        self.write_column(position, res);
+        res
+    }
+
     unsafe fn mul_hi_lo_signed(
         &mut self,
         x: &Self::Variable,

From 95098af4c18c79cc880f1e2da0dd76399b470423 Mon Sep 17 00:00:00 2001
From: Danny Willems <be.danny.willems@gmail.com>
Date: Mon, 25 Nov 2024 10:46:42 +0100
Subject: [PATCH 2/2] o1vm/riscv32im: simplify mul_lo_signed implementation

---
 o1vm/src/interpreters/riscv32im/witness.rs | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/o1vm/src/interpreters/riscv32im/witness.rs b/o1vm/src/interpreters/riscv32im/witness.rs
index 658048bf99..3484ad0a10 100644
--- a/o1vm/src/interpreters/riscv32im/witness.rs
+++ b/o1vm/src/interpreters/riscv32im/witness.rs
@@ -462,9 +462,9 @@ impl<Fp: Field> InterpreterEnv for Env<Fp> {
         y: &Self::Variable,
         position: Self::Position,
     ) -> Self::Variable {
-        let x: u32 = (*x).try_into().unwrap();
-        let y: u32 = (*y).try_into().unwrap();
-        let res = (((x as i32) as i64) * ((y as i32) as i64)) as u64;
+        let x: i32 = (*x).try_into().unwrap();
+        let y: i32 = (*y).try_into().unwrap();
+        let res = ((x as i64) * (y as i64)) as u64;
         let res = (res & ((1 << 32) - 1)) as u32;
         let res = res as u64;
         self.write_column(position, res);