From 4886ee3a57d66a279dcc17b757d94f98f9d28f21 Mon Sep 17 00:00:00 2001
From: Shahar Samocha <shahars@starkware.co>
Date: Tue, 7 Jan 2025 12:59:49 +0200
Subject: [PATCH] generate enabler column

---
 .../crates/prover/src/components/utils.rs     | 33 ++++++++++++++++++-
 stwo_cairo_prover/crates/prover/src/lib.rs    |  1 +
 2 files changed, 33 insertions(+), 1 deletion(-)

diff --git a/stwo_cairo_prover/crates/prover/src/components/utils.rs b/stwo_cairo_prover/crates/prover/src/components/utils.rs
index 457aad6e..215c3447 100644
--- a/stwo_cairo_prover/crates/prover/src/components/utils.rs
+++ b/stwo_cairo_prover/crates/prover/src/components/utils.rs
@@ -81,12 +81,23 @@ impl AtomicMultiplicityColumn {
     }
 }
 
+/// Generates a padding column for the given padding offset.
+/// The padding column is a MultiplicityColumn of length next_power_of_two(padding_offset) where
+/// 1. The first `padding_offset` elements set to 1;
+/// 2. Otherwise set to 0.
+pub fn gen_padding_column(padding_offset: usize) -> MultiplicityColumn {
+    let log_size = padding_offset.next_power_of_two().ilog2();
+    let mut padding_column = MultiplicityColumn::new(1 << log_size);
+    (0..padding_offset).for_each(|i| padding_column.increase_at(i as u32));
+    padding_column
+}
+
 #[cfg(test)]
 mod tests {
     use num_traits::{One, Zero};
     use rand::rngs::SmallRng;
     use rand::{Rng, SeedableRng};
-    use stwo_prover::core::backend::simd::m31::N_LANES;
+    use stwo_prover::core::backend::simd::m31::{PackedM31, N_LANES};
     use stwo_prover::core::fields::m31::M31;
 
     #[test]
@@ -107,4 +118,24 @@ mod tests {
             assert!(res_chunk.to_array() == expected_chunk);
         }
     }
+
+    #[test]
+    fn test_gen_padding_column() {
+        let n_calls = 30;
+
+        let enabler_column = super::gen_padding_column(n_calls);
+
+        for (i, val) in enabler_column
+            .into_simd_vec()
+            .into_iter()
+            .flat_map(PackedM31::to_array)
+            .enumerate()
+        {
+            if i < n_calls {
+                assert_eq!(val, M31::one());
+            } else {
+                assert_eq!(val, M31::zero());
+            }
+        }
+    }
 }
diff --git a/stwo_cairo_prover/crates/prover/src/lib.rs b/stwo_cairo_prover/crates/prover/src/lib.rs
index f0e1cc9e..05480300 100644
--- a/stwo_cairo_prover/crates/prover/src/lib.rs
+++ b/stwo_cairo_prover/crates/prover/src/lib.rs
@@ -1,4 +1,5 @@
 #![feature(
+    exact_size_is_empty,
     trait_upcasting,
     portable_simd,
     iter_array_chunks,