Make modular reduction work for large byte sizes

src/fields/fp/arkworks.rs

@@ -52,13 +52,15 @@ impl PrimeField for Fp {
     }
 
     fn from_le_bytes_mod_order(bytes: &[u8]) -> Self {
-        assert!(bytes.len() == 48);
-
-        let mut t = [0u8; 48];
-        t.copy_from_slice(&bytes[..48]);
-        let modulus_field_montgomery = Fp::from_raw_bytes(&t);
-
-        modulus_field_montgomery
+        bytes
+            .chunks(48)
+            .map(|x| {
+                let mut padded = [0u8; 48];
+                padded[..x.len()].copy_from_slice(x);
+                Self::from_raw_bytes(&padded)
+            }) // [X, 2^(384) * X, ...]
+            .rev()
+            .fold(Self::zero(), |acc, x| acc * (FIELD_SIZE_POWER_OF_TWO) + x) // let acc =
     }
 }
 
@@ -578,7 +580,7 @@ mod tests {
 
     proptest! {
         #[test]
-        fn test_from_le_bytes_mod_order_vs_naive(bytes in any::<[u8; 48]>()) {
+        fn test_from_le_bytes_mod_order_vs_naive(bytes in any::<[u8; 128]>()) {
             let way1 = Fp::from_le_bytes_mod_order(&bytes);
             let way2 = naive_from_le_bytes_mod_order(&bytes);
             assert_eq!(way1, way2);

src/fields/fp/u32/arkworks_constants.rs

@@ -54,3 +54,8 @@ pub const TWO_ADIC_ROOT_OF_UNITY: Fp = Fp::from_montgomery_limbs([
     2031790878, 3754616354, 3204826524, 1913374628, 226001622, 631062918, 2984565398, 3626713688,
     1739907172, 3086590412, 1450066569, 16622719,
 ]);
+
+pub const FIELD_SIZE_POWER_OF_TWO: Fp = Fp::from_montgomery_limbs([
+    2483080482, 3079039084, 2953064881, 53083306, 1658238061, 581300497, 2189280172, 3219094787,
+    1098451961, 2206110448, 512838536, 7208139,
+]);

src/fields/fp/u64/arkworks_constants.rs

@@ -66,3 +66,12 @@ pub const TWO_ADIC_ROOT_OF_UNITY: Fp = Fp::from_montgomery_limbs([
     13256804877427073124,
     71394035925664393,
 ]);
+
+pub const FIELD_SIZE_POWER_OF_TWO: Fp = Fp::from_montgomery_limbs([
+    13224372171368877346,
+    227991066186625457,
+    2496666625421784173,
+    13825906835078366124,
+    9475172226622360569,
+    30958721782860680,
+]);

src/fields/fq/arkworks.rs

@@ -5,6 +5,7 @@ use ark_serialize::{
     CanonicalDeserialize, CanonicalDeserializeWithFlags, CanonicalSerialize,
     CanonicalSerializeWithFlags, Compress, EmptyFlags, Flags, SerializationError, Valid, Validate,
 };
+use ark_std::iterable::Iterable;
 use ark_std::{rand, str::FromStr, string::ToString, One, Zero};
 use core::convert::TryInto;
 use core::{
@@ -52,13 +53,15 @@ impl PrimeField for Fq {
     }
 
     fn from_le_bytes_mod_order(bytes: &[u8]) -> Self {
-        assert!(bytes.len() == 32);
-
-        let mut t = [0u8; 32];
-        t.copy_from_slice(&bytes[..32]);
-        let modulus_field_montgomery = Fq::from_raw_bytes(&t);
-
-        modulus_field_montgomery
+        bytes
+            .chunks(32)
+            .map(|x| {
+                let mut padded = [0u8; 32];
+                padded[..x.len()].copy_from_slice(x);
+                Self::from_raw_bytes(&padded)
+            }) // [X, 2^256 * X, ...]
+            .rev()
+            .fold(Self::zero(), |acc, x| acc * (FIELD_SIZE_POWER_OF_TWO) + x) // let acc =
     }
 }
 
@@ -575,7 +578,7 @@ mod tests {
 
     proptest! {
         #[test]
-        fn test_from_le_bytes_mod_order_vs_naive(bytes in any::<[u8; 32]>()) {
+        fn test_from_le_bytes_mod_order_vs_naive(bytes in any::<[u8; 80]>()) {
             let way1 = Fq::from_le_bytes_mod_order(&bytes);
             let way2 = naive_from_le_bytes_mod_order(&bytes);
             assert_eq!(way1, way2);

src/fields/fq/u32/arkworks_constants.rs

@@ -43,3 +43,7 @@ pub const MULTIPLICATIVE_GENERATOR: Fq = Fq::from_montgomery_limbs([
 pub const TWO_ADIC_ROOT_OF_UNITY: Fq = Fq::from_montgomery_limbs([
     3661289032, 2944457293, 4231536044, 1579301595, 3002672421, 62522982, 1005564110, 261123163,
 ]);
+
+pub const FIELD_SIZE_POWER_OF_TWO: Fq = Fq::from_montgomery_limbs([
+    3093398907, 634746810, 2288015647, 3425445813, 3856434579, 2815164559, 4025600313, 18864871,
+]);

src/fields/fq/u64/arkworks_constants.rs

@@ -52,3 +52,10 @@ pub const TWO_ADIC_ROOT_OF_UNITY: Fq = Fq::from_montgomery_limbs([
     268534165941069093,
     1121515446318641358,
 ]);
+
+pub const FIELD_SIZE_POWER_OF_TWO: Fq = Fq::from_montgomery_limbs([
+    2726216793283724667,
+    14712177743343147295,
+    12091039717619697043,
+    81024008013859129,
+]);

src/fields/fr/arkworks.rs

@@ -52,13 +52,15 @@ impl PrimeField for Fr {
     }
 
     fn from_le_bytes_mod_order(bytes: &[u8]) -> Self {
-        assert!(bytes.len() == 32);
-
-        let mut t = [0u8; 32];
-        t.copy_from_slice(&bytes[..32]);
-        let modulus_field_montgomery = Fr::from_raw_bytes(&t);
-
-        modulus_field_montgomery
+        bytes
+            .chunks(32)
+            .map(|x| {
+                let mut padded = [0u8; 32];
+                padded[..x.len()].copy_from_slice(x);
+                Self::from_raw_bytes(&padded)
+            }) // [X, 2^256 * X, ...]
+            .rev()
+            .fold(Self::zero(), |acc, x| acc * (FIELD_SIZE_POWER_OF_TWO) + x) // let acc =
     }
 }
 
@@ -561,7 +563,7 @@ mod tests {
 
     proptest! {
         #[test]
-        fn test_from_le_bytes_mod_order_vs_naive(bytes in any::<[u8; 32]>()) {
+        fn test_from_le_bytes_mod_order_vs_naive(bytes in any::<[u8; 80]>()) {
             let way1 = Fr::from_le_bytes_mod_order(&bytes);
             let way2 = naive_from_le_bytes_mod_order(&bytes);
             assert_eq!(way1, way2);

src/fields/fr/u32/arkworks_constants.rs

@@ -39,3 +39,7 @@ pub const MULTIPLICATIVE_GENERATOR: Fr = Fr::from_montgomery_limbs([
 pub const TWO_ADIC_ROOT_OF_UNITY: Fr = Fr::from_montgomery_limbs([
     4072134089, 3532211007, 687987897, 3182963395, 1946006545, 2981045345, 3353731427, 11842004,
 ]);
+
+pub const FIELD_SIZE_POWER_OF_TWO: Fr = Fr::from_montgomery_limbs([
+    1784009822, 928422349, 2054412915, 4130980853, 3439491617, 3389392028, 4009941057, 75160094,
+]);

src/fields/fr/u64/arkworks_constants.rs

@@ -45,3 +45,10 @@ pub const TWO_ADIC_ROOT_OF_UNITY: Fr = Fr::from_montgomery_limbs([
     12803492244414043445,
     50841023252832411,
 ]);
+
+pub const FIELD_SIZE_POWER_OF_TWO: Fr = Fr::from_montgomery_limbs([
+    3987543627614508126,
+    17742427666091596403,
+    14557327917022607905,
+    322810149704226881,
+]);