From dea6db00ac54e24389870ed953f3ad7a66e4f5e8 Mon Sep 17 00:00:00 2001
From: wborgeaud <williamborgeaud@gmail.com>
Date: Thu, 10 Jun 2021 17:45:45 +0200
Subject: [PATCH] Rotation gadgets

---
 src/field/extension_field/algebra.rs |  1 -
 src/fri/recursive_verifier.rs        |  2 +-
 src/fri/verifier.rs                  |  2 +-
 src/gadgets/mod.rs                   |  1 +
 src/gadgets/rotate.rs                | 66 ++++++++++++++++++++++++++++
 5 files changed, 69 insertions(+), 3 deletions(-)
 create mode 100644 src/gadgets/rotate.rs

diff --git a/src/field/extension_field/algebra.rs b/src/field/extension_field/algebra.rs
index eac0bbd8..f61f173b 100644
--- a/src/field/extension_field/algebra.rs
+++ b/src/field/extension_field/algebra.rs
@@ -218,7 +218,6 @@ mod tests {
         let y = ExtensionAlgebra::from_basefield_array(arr1);
         let z = x * y;
 
-        dbg!(z.0, mul_mle(ts.clone()));
         assert_eq!(z.0, mul_mle(ts));
     }
 
diff --git a/src/fri/recursive_verifier.rs b/src/fri/recursive_verifier.rs
index 25fb7687..4f8c3864 100644
--- a/src/fri/recursive_verifier.rs
+++ b/src/fri/recursive_verifier.rs
@@ -326,7 +326,7 @@ impl<F: Extendable<D>, const D: usize> CircuitBuilder<F, D> {
                 }
             }
             domain_size = next_domain_size;
-            old_x_index = x_index;
+            old_x_index = low_x_index;
             x_index = high_x_index;
         }
 
diff --git a/src/fri/verifier.rs b/src/fri/verifier.rs
index 41baa84e..6275ada6 100644
--- a/src/fri/verifier.rs
+++ b/src/fri/verifier.rs
@@ -279,7 +279,7 @@ fn fri_verifier_query_round<F: Field + Extendable<D>, const D: usize>(
             }
         }
         domain_size = next_domain_size;
-        old_x_index = x_index;
+        old_x_index = x_index & (arity - 1);
         x_index >>= arity_bits;
     }
 
diff --git a/src/gadgets/mod.rs b/src/gadgets/mod.rs
index 636f8afc..137b991e 100644
--- a/src/gadgets/mod.rs
+++ b/src/gadgets/mod.rs
@@ -3,5 +3,6 @@ pub mod hash;
 pub mod interpolation;
 pub mod polynomial;
 pub mod range_check;
+pub mod rotate;
 pub mod split_base;
 pub(crate) mod split_join;
diff --git a/src/gadgets/rotate.rs b/src/gadgets/rotate.rs
new file mode 100644
index 00000000..fa5579f7
--- /dev/null
+++ b/src/gadgets/rotate.rs
@@ -0,0 +1,66 @@
+use crate::circuit_builder::CircuitBuilder;
+use crate::field::extension_field::Extendable;
+use crate::field::field::Field;
+use crate::gates::base_sum::BaseSumGate;
+use crate::generator::SimpleGenerator;
+use crate::target::Target;
+use crate::witness::PartialWitness;
+
+impl<F: Extendable<D>, const D: usize> CircuitBuilder<F, D> {
+    /// Selects `x` or `y` based on `b`, which is assumed to be binary.
+    /// In particular, this returns `if b { x } else { y }`.
+    /// Note: This does not range-check `b`.
+    pub fn select(&mut self, b: Target, x: Target, y: Target) -> Target {
+        let b_y_minus_y = self.mul_sub(b, y, y);
+        self.mul_sub(b, x, b_y_minus_y)
+    }
+
+    /// Left-rotates an array if `b=1` else return the same array.
+    pub fn rotate_once(&mut self, b: Target, v: Vec<Target>, len: usize) -> Vec<Target> {
+        debug_assert_eq!(v.len(), len);
+        let mut res = Vec::new();
+
+        for i in 0..len {
+            res.push(self.select(b, v[(i + 1) % len], v[i]));
+        }
+
+        res
+    }
+
+    pub fn split_unary(&mut self, x: Target, len: usize) -> Vec<Target> {
+        todo!()
+    }
+
+    /// Left-rotates an array by `num_rotation`. Assumes that `num_rotation` is range-checked to be
+    /// less than `len`.
+    pub fn rotate(&mut self, num_rotation: Target, v: Vec<Target>, len: usize) -> Vec<Target> {
+        // Decompose `num_rotation` into `len` 1-ary limbs, possibly with a new gate.
+        // Then apply `rotate_once` `len` time using the 1-ary limbs.
+        todo!()
+    }
+}
+
+#[derive(Debug)]
+struct UnaryBaseGenerator {
+    integer: Target,
+    len: usize,
+    limbs: Vec<Target>,
+}
+
+impl<F: Field> SimpleGenerator<F> for UnaryBaseGenerator {
+    fn dependencies(&self) -> Vec<Target> {
+        vec![self.integer]
+    }
+
+    fn run_once(&self, witness: &PartialWitness<F>) -> PartialWitness<F> {
+        let mut integer_value = witness.get_target(self.integer).to_canonical_u64();
+        let low = integer_value & ((1 << self.n_log) - 1);
+        let high = integer_value >> self.n_log;
+
+        let mut result = PartialWitness::new();
+        result.set_target(self.low, F::from_canonical_u64(low));
+        result.set_target(self.high, F::from_canonical_u64(high));
+
+        result
+    }
+}