From 0514cd9646fa9f182c96dfb7bbd2e5e9672f782d Mon Sep 17 00:00:00 2001
From: Nicholas Ward <npward@berkeley.edu>
Date: Thu, 16 Jun 2022 23:37:51 -0700
Subject: [PATCH] addressed comments

---
 evm/src/cpu/columns.rs         |  1 -
 evm/src/memory/memory_stark.rs | 27 +++++++++------------------
 2 files changed, 9 insertions(+), 19 deletions(-)

diff --git a/evm/src/cpu/columns.rs b/evm/src/cpu/columns.rs
index 3c90c673..296744c4 100644
--- a/evm/src/cpu/columns.rs
+++ b/evm/src/cpu/columns.rs
@@ -163,7 +163,6 @@ const NUM_MEMORY_VALUE_LIMBS: usize = 8;
 
 pub(crate) const CLOCK: usize = SIMPLE_LOGIC_DIFF_INV + 1;
 
-
 const USES_MEMOP_START: usize = CLOCK + 1;
 pub const fn uses_memop(op: usize) -> usize {
     debug_assert!(op < NUM_MEMORY_OPS);
diff --git a/evm/src/memory/memory_stark.rs b/evm/src/memory/memory_stark.rs
index d74c65e8..09e3320d 100644
--- a/evm/src/memory/memory_stark.rs
+++ b/evm/src/memory/memory_stark.rs
@@ -124,25 +124,16 @@ pub fn generate_first_change_flags<F: RichField>(
     let mut segment_first_change = Vec::new();
     let mut virtual_first_change = Vec::new();
     for idx in 0..num_ops - 1 {
-        let this_context_first_change = if context[idx] != context[idx + 1] {
-            F::ONE
-        } else {
-            F::ZERO
-        };
-        let this_segment_first_change = if segment[idx] != segment[idx + 1] {
-            F::ONE * (F::ONE - this_context_first_change)
-        } else {
-            F::ZERO
-        };
-        let this_virtual_first_change = if virtuals[idx] != virtuals[idx + 1] {
-            F::ONE * (F::ONE - this_context_first_change) * (F::ONE - this_segment_first_change)
-        } else {
-            F::ZERO
-        };
+        let this_context_first_change = context[idx] != context[idx + 1];
+        let this_segment_first_change =
+            segment[idx] != segment[idx + 1] && !this_context_first_change;
+        let this_virtual_first_change = virtuals[idx] != virtuals[idx + 1]
+            && !this_segment_first_change
+            && !this_context_first_change;
 
-        context_first_change.push(this_context_first_change);
-        segment_first_change.push(this_segment_first_change);
-        virtual_first_change.push(this_virtual_first_change);
+        context_first_change.push(F::from_bool(this_context_first_change));
+        segment_first_change.push(F::from_bool(this_segment_first_change));
+        virtual_first_change.push(F::from_bool(this_virtual_first_change));
     }
 
     context_first_change.push(F::ZERO);