From 6393f638266f621ba173918c38e07598076b5538 Mon Sep 17 00:00:00 2001
From: svv232 <saidcooldude@gmail.com>
Date: Sun, 1 Dec 2024 16:52:03 -0500
Subject: [PATCH] branch equal instruction implementation

---
 .../src/interpreters/riscv32im/interpreter.rs | 26 +++++++++++++++++--
 1 file changed, 24 insertions(+), 2 deletions(-)

diff --git a/o1vm/src/interpreters/riscv32im/interpreter.rs b/o1vm/src/interpreters/riscv32im/interpreter.rs
index 462ded8981..904dbf67c9 100644
--- a/o1vm/src/interpreters/riscv32im/interpreter.rs
+++ b/o1vm/src/interpreters/riscv32im/interpreter.rs
@@ -2069,7 +2069,7 @@ pub fn interpret_sbtype<Env: InterpreterEnv>(env: &mut Env, instr: SBInstruction
     /* fetch instruction pointer from the program state */
     let instruction_pointer = env.get_instruction_pointer();
     /* compute the next instruction ptr and add one, as well record raml lookup */
-    let _next_instruction_pointer = env.get_next_instruction_pointer();
+    let next_instruction_pointer = env.get_next_instruction_pointer();
     /* read instruction from ip address */
     let instruction = {
         let v0 = env.read_memory(&instruction_pointer);
@@ -2157,7 +2157,29 @@ pub fn interpret_sbtype<Env: InterpreterEnv>(env: &mut Env, instr: SBInstruction
 
     match instr {
         SBInstruction::BranchEq => {
-            unimplemented!("BranchEq")
+            // beq: if (x[rs1] == x[rs2]) pc += sext(offset)
+            let local_rs1 = env.read_register(&rs1);
+            let local_rs2 = env.read_register(&rs2);
+
+            let equals = env.equal(&local_rs1, &local_rs2);
+            let offset = (Env::constant(1) - equals.clone()) * Env::constant(4) + equals * imm0_12;
+            let offset = env.sign_extend(&offset, 12);
+            let addr = {
+                let res_scratch = env.alloc_scratch();
+                let overflow_scratch = env.alloc_scratch();
+                let (res, _overflow) = unsafe {
+                    env.add_witness(
+                        &next_instruction_pointer,
+                        &offset,
+                        res_scratch,
+                        overflow_scratch,
+                    )
+                };
+                // FIXME: Requires a range check
+                res
+            };
+            env.set_instruction_pointer(next_instruction_pointer);
+            env.set_next_instruction_pointer(addr);
         }
         SBInstruction::BranchNeq => {
             // bne: if (x[rs1] != x[rs2]) pc += sext(offset)