add quickcheck tests and fix off-by-one bug introduced in #31 (#35)

* add quickcheck tests and fix off-by-one bug introduced in #31

* address review comment

* replace saturating_add with max()

reed-solomon-novelpoly/Cargo.toml

@@ -35,6 +35,7 @@ itertools = "0.12"
 reed-solomon-tester = { path = "../reed-solomon-tester" }
 rand = { version = "0.8.3", features = ["alloc", "small_rng"] }
 assert_matches = "1.5.0"
+quickcheck = { version = "1.0.3", default-features = false }
 
 [features]
 default = []

reed-solomon-novelpoly/src/field/inc_encode.rs

@@ -190,7 +190,7 @@ pub fn encode_sub_plain(bytes: &[u8], n: usize, k: usize) -> Result<Vec<Additive
 	// so we get a buffer of size `N` in `GF` symbols
 	let mut elm_data = vec![Additive(0); n];
 
-	for i in 0..(bytes_len / 2) {
+	for i in 0..((bytes_len + 1) / 2) {
 		elm_data[i] = Additive(Elt::from_be_bytes([
 			bytes.get(2 * i).copied().unwrap_or_default(),
 			bytes.get(2 * i + 1).copied().unwrap_or_default(),
@@ -241,7 +241,7 @@ pub fn encode_sub_faster8(bytes: &[u8], n: usize, k: usize) -> Result<Vec<Additi
 	// so we get a buffer of size `N` in `GF` symbols
 	let mut elm_data = vec![Additive(0); n];
 
-	for i in 0..(bytes_len / 2) {
+	for i in 0..((bytes_len + 1) / 2) {
 		elm_data[i] = Additive(Elt::from_be_bytes([
 			bytes.get(2 * i).map(|x| *x).unwrap_or_default(),
 			bytes.get(2 * i + 1).map(|x| *x).unwrap_or_default(),

reed-solomon-novelpoly/src/novel_poly_basis/tests.rs

@@ -9,6 +9,7 @@ use rand::rngs::SmallRng;
 use rand::seq::index::IndexVec;
 use rand::thread_rng;
 use reed_solomon_tester::*;
+use quickcheck::{Arbitrary, Gen, QuickCheck};
 
 /// Generate a random index
 fn rand_gf_element() -> Additive {
@@ -463,3 +464,32 @@ fn shard_len_is_reasonable() {
 	// needs 3 bytes to fit, rounded up to next even number.
 	assert_eq!(rs.shard_len(19), 6);
 }
+
+#[derive(Clone, Debug)]
+struct ArbitraryData(Vec<u8>);
+
+impl Arbitrary for ArbitraryData {
+	fn arbitrary(g: &mut Gen) -> Self {
+		// Limit the len to 1 mib, otherwise the test will take forever
+		let len = (u32::arbitrary(g) % (1024 * 1024)).max(2);
+
+		let data: Vec<u8> = (0..len).map(|_| u8::arbitrary(g)).collect();
+
+		ArbitraryData(data)
+	}
+}
+
+#[test]
+fn round_trip_quickcheck() {
+	fn property(available_data: ArbitraryData, n_validators: u16) {
+		let n_validators = n_validators.max(2);
+		let wanted_k = (n_validators as usize - 1) / 3 + 1;
+		let rs = CodeParams::derive_parameters(n_validators as usize, wanted_k).unwrap().make_encoder();
+		let chunks = rs.encode::<WrappedShard>(&available_data.0).unwrap();
+		let mut res = rs.reconstruct(chunks.into_iter().take(wanted_k).map(|s| Some(s)).collect()).unwrap();
+		res.truncate(available_data.0.len());
+		assert_eq!(res, available_data.0);
+	}
+
+	QuickCheck::new().quickcheck(property as fn(ArbitraryData, u16))
+}