From 88c2d69e32249e447a4b568fa492afaa99a1236d Mon Sep 17 00:00:00 2001
From: Filip Krawczyk <kotmawszy@gmail.com>
Date: Thu, 21 Dec 2023 10:04:10 +0100
Subject: [PATCH] Implement read_felt_from_prover

---
 src/channel/channel.cairo            | 10 ++++++++++
 src/channel/tests/test_channel.cairo | 10 ++++++++++
 2 files changed, 20 insertions(+)

diff --git a/src/channel/channel.cairo b/src/channel/channel.cairo
index 1a4997130..452b03bcf 100644
--- a/src/channel/channel.cairo
+++ b/src/channel/channel.cairo
@@ -51,4 +51,14 @@ impl ChannelImpl of ChannelTrait {
         };
         res
     }
+
+    fn read_felt_from_prover(ref self: Channel, value: felt252) {
+        let value_u256: u256 = value.into();
+        let mut hash_data = ArrayTrait::<u32>::new();
+
+        (self.digest + 1).to_array_be(ref hash_data);
+        value_u256.to_array_be(ref hash_data);
+
+        self.digest = blake2s(hash_data).flip_endiannes();
+    }
 }
diff --git a/src/channel/tests/test_channel.cairo b/src/channel/tests/test_channel.cairo
index 273ba3a9c..4f919109c 100644
--- a/src/channel/tests/test_channel.cairo
+++ b/src/channel/tests/test_channel.cairo
@@ -31,3 +31,13 @@ fn test_random_uint256_to_prover() {
         'invalid random uint256'
     );
 }
+
+#[test]
+#[available_gas(9999999999)]
+fn test_read_felt_from_prover() {
+    let mut channel = ChannelTrait::new(0);
+
+    channel.read_felt_from_prover(0xffffffffffffffffffffffffffffffffffffffff);
+
+    assert(channel.digest == 0xb056692f5fc4f27dedd1fb6269b02c542a415f1d84555708a354ffb25cf97ad5, 'invalid read felt');
+}