read_felt_vector_from_prover

HerodotusDev · Dec 21, 2023 · 386fbed · 386fbed
1 parent e5be56c
commit 386fbed
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Showing 2 changed files with 30 additions and 5 deletions.
diff --git a/src/channel/channel.cairo b/src/channel/channel.cairo
@@ -8,7 +8,8 @@ const C_PRIME_AS_UINT256_HIGH: u128 =
     329648542954659146201578277794459156480; // 31 * 0x8000000000000110000000000000000;
 const STARK_PRIME: u256 =
     3618502788666131213697322783095070105623107215331596699973092056135872020481;
-const INVERSE_2_TO_256_MOD_STARK_PRIME: felt252 =
+const MONTGOMERY_R: felt252 = 3618502788666127798953978732740734578953660990361066340291730267701097005025; // 2**256 % STARK_PRIME
+const MONTGOMERY_R_INVERSE_MOD_STARK_PRIME: felt252 =
     113078212145816603762751633895895194930089271709401121343797004406777446400;
 
 #[derive(Drop)]
@@ -44,7 +45,7 @@ impl ChannelImpl of ChannelTrait {
                 if (rand < u256 { low: C_PRIME_AS_UINT256_LOW, high: C_PRIME_AS_UINT256_HIGH }) {
                     n -= 1;
                     let to_append = (rand % STARK_PRIME).try_into().unwrap();
-                    res.append(to_append * INVERSE_2_TO_256_MOD_STARK_PRIME);
+                    res.append(to_append * MONTGOMERY_R_INVERSE_MOD_STARK_PRIME);
                 }
             } else {
                 break;
@@ -64,8 +65,27 @@ impl ChannelImpl of ChannelTrait {
         self.digest = blake2s(hash_data).flip_endiannes();
     }
 
-    fn read_felts_from_prover(ref self: Channel, values: Array<felt252>) {
-        let hashed = poseidon_hash_span(values.span());
+    fn read_felts_from_prover(ref self: Channel, values: Span<felt252>) {
+        let hashed = poseidon_hash_span(values);
         self.read_felt_from_prover(hashed);
     }
+
+    fn read_felt_vector_from_prover(ref self: Channel, values: Span<felt252>) {
+        let mut hash_data = ArrayTrait::<u32>::new();
+
+        assert(self.digest.low != 0xffffffffffffffffffffffffffffffff, 'digest low is 2^128-1');
+        (self.digest + 1).to_array_be(ref hash_data);
+
+        let mut i = 0;
+        loop {
+            if i == values.len() {
+                break;
+            };
+            let value_u256: u256 = (*values[i] * MONTGOMERY_R).into();
+            value_u256.to_array_be(ref hash_data);
+            i += 1;
+        };
+
+        self.digest = blake2s(hash_data).flip_endiannes();
+    }
 }
diff --git a/src/channel/tests/test_channel.cairo b/src/channel/tests/test_channel.cairo
@@ -46,8 +46,13 @@ fn test_read_from_prover() {
     arr.append(2);
     arr.append(3);
     arr.append(-1);
-    channel.read_felts_from_prover(arr);
+    channel.read_felts_from_prover(arr.span());
 
     assert(channel.counter == 0, 'invalid read felts');
     assert(channel.digest == 0x135bc3291210bb6248a09cea1a97b0023c5602b18a9e0786aeed16352972504, 'invalid read felts');
+
+    channel.read_felt_vector_from_prover(arr.span());
+
+    assert(channel.counter == 0, 'invalid read felts');
+    assert(channel.digest == 0x413b1e08fe14f181acc48007a89e4d044a9edb54523e8eae5829fde606d4074d, 'invalid read felts');
 }