From 4370950eb5a06c767140f4c27e1798487b01c063 Mon Sep 17 00:00:00 2001
From: Bartosz Nowak <bartekn337@gmail.com>
Date: Wed, 20 Dec 2023 19:27:38 +0100
Subject: [PATCH] fri_commit

---
 src/channel/channel.cairo | 23 +++++++++++++++++
 src/fri/fri.cairo         | 54 ++++++++++++++++++++++++++++++++++++++-
 src/fri/fri_config.cairo  |  4 +--
 3 files changed, 78 insertions(+), 3 deletions(-)

diff --git a/src/channel/channel.cairo b/src/channel/channel.cairo
index 120fbbeeb..7e3375ef7 100644
--- a/src/channel/channel.cairo
+++ b/src/channel/channel.cairo
@@ -17,6 +17,20 @@ struct Channel {
     counter: u256,
 }
 
+// A wrapper around felt with a guarantee that the felt must be read from the channel before
+// use.
+#[derive(Drop)]
+struct ChannelUnsentFelt {
+    value: felt252,
+}
+
+// A wrapper around felt with a guarantee that the felt was read from the channel as data from the
+// prover.
+#[derive(Drop)]
+struct ChannelSentFelt {
+    value: felt252,
+}
+
 #[generate_trait]
 impl ChannelImpl of ChannelTrait {
     fn new(digest: u256) -> Channel {
@@ -61,4 +75,13 @@ impl ChannelImpl of ChannelTrait {
         };
         res
     }
+
+    // Reads a field element vector from the prover. Unlike read_felts_from_prover, this hashes all the
+    // field elements at once. See Channel.
+    fn read_felt_vector_from_prover(
+        ref self: Channel, values: Span<ChannelUnsentFelt>
+    ) -> Array<ChannelSentFelt> {
+        let sent_felts = ArrayTrait::<ChannelSentFelt>::new();
+        sent_felts
+    }
 }
diff --git a/src/fri/fri.cairo b/src/fri/fri.cairo
index 6a7e95ead..2400653be 100644
--- a/src/fri/fri.cairo
+++ b/src/fri/fri.cairo
@@ -1,3 +1,4 @@
+use core::array::SpanTrait;
 use core::traits::Destruct;
 use cairo_verifier::channel::channel::ChannelTrait;
 use cairo_verifier::table_commitment::{
@@ -6,6 +7,32 @@ use cairo_verifier::table_commitment::{
 use core::array::ArrayTrait;
 use cairo_verifier::table_commitment::table_commit;
 use cairo_verifier::channel::channel::Channel;
+use cairo_verifier::channel::channel::{ChannelUnsentFelt, ChannelSentFelt};
+use cairo_verifier::fri::fri_config::FriConfig;
+use cairo_verifier::common::math;
+
+// Commitment values for FRI. Used to generate a commitment by "reading" these values
+// from the channel.
+#[derive(Drop, Copy)]
+struct FriUnsentCommitment {
+    // Array of size n_layers - 1 containing unsent table commitments for each inner layer.
+    inner_layers: Span<TableUnsentCommitment>,
+    // Array of size 2**log_last_layer_degree_bound containing coefficients for the last layer
+    // polynomial.
+    last_layer_coefficients: Span<ChannelUnsentFelt>,
+}
+
+#[derive(Drop, Copy)]
+struct FriCommitment {
+    config: FriConfig,
+    // Array of size n_layers - 1 containing table commitments for each inner layer.
+    inner_layers: Span<TableCommitment>,
+    // Array of size n_layers, of one evaluation point for each layer.
+    eval_points: Span<felt252>,
+    // Array of size 2**log_last_layer_degree_bound containing coefficients for the last layer
+    // polynomial.
+    last_layer_coefficients: Span<ChannelSentFelt>,
+}
 
 // A FRI phase with N layers starts with a single input layer.
 // Afterwards, there are N - 1 inner layers resulting from FRI-folding each preceding layer.
@@ -34,7 +61,6 @@ fn fri_commit_rounds(
     configs: Span<TableCommitmentConfig>,
     unsent_commitments: Span<TableUnsentCommitment>,
     step_sizes: Span<felt252>,
-    commitments: Span<TableCommitment>,
 ) -> (Array<TableCommitment>, Array<felt252>) {
     let mut commitments = ArrayTrait::<TableCommitment>::new();
     let mut eval_points = ArrayTrait::<felt252>::new();
@@ -54,3 +80,29 @@ fn fri_commit_rounds(
 
     (commitments, eval_points)
 }
+
+fn fri_commit(
+    ref channel: Channel, unsent_commitment: FriUnsentCommitment, config: FriConfig
+) -> FriCommitment {
+    assert((*config.fri_step_sizes.at(0)) == 0, 'Invalid value');
+
+    let (commitments, eval_points) = fri_commit_rounds(
+        ref channel,
+        config.n_layers,
+        config.inner_layers,
+        unsent_commitment.inner_layers,
+        config.fri_step_sizes,
+    );
+
+    // Read last layer coefficients.
+    let n_coefficients = math::pow(2, config.log_last_layer_degree_bound);
+    let coefficients = channel
+        .read_felt_vector_from_prover(unsent_commitment.last_layer_coefficients);
+
+    FriCommitment {
+        config: config,
+        inner_layers: commitments.span(),
+        eval_points: eval_points.span(),
+        last_layer_coefficients: coefficients.span()
+    }
+}
diff --git a/src/fri/fri_config.cairo b/src/fri/fri_config.cairo
index 4f4fb4e60..e101a5dd9 100644
--- a/src/fri/fri_config.cairo
+++ b/src/fri/fri_config.cairo
@@ -9,7 +9,7 @@ const MAX_LAST_LAYER_LOG_DEGREE_BOUND: u32 = 15;
 const MAX_FRI_LAYERS: u32 = 15;
 const MAX_FRI_STEP: u32 = 4;
 
-#[derive(Drop)]
+#[derive(Drop, Copy)]
 struct FriConfig {
     // Log2 of the size of the input layer to FRI.
     log_input_size: felt252,
@@ -17,7 +17,7 @@ struct FriConfig {
     n_layers: felt252,
     // Array of size n_layers - 1, each entry is a configuration of a table commitment for the
     // corresponding inner layer.
-    inner_layers: Array<TableCommitmentConfig>,
+    inner_layers: Span<TableCommitmentConfig>,
     // Array of size n_layers, each entry represents the FRI step size,
     // i.e. the number of FRI-foldings between layer i and i+1.
     fri_step_sizes: Span<felt252>,