fix: fix broken tests in runtime_bignum_test.nr (#39)

Co-authored-by: Khashayar Barooti <[email protected]> Co-authored-by: Tom French <[email protected]> Co-authored-by: Tom French <[email protected]> Co-authored-by: kashbrti <[email protected]>
noir-lang · Nov 7, 2024 · 63e6c85 · 63e6c85
1 parent 08c4151
commit 63e6c85
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Showing 6 changed files with 83 additions and 110 deletions.
diff --git a/.gitignore b/.gitignore
@@ -1 +1,2 @@
-target
+target
+.vscode/launch.json
diff --git a/src/fns/constrained_ops.nr b/src/fns/constrained_ops.nr
@@ -64,7 +64,8 @@ pub(crate) fn derive_from_seed<let N: u32, let MOD_BITS: u32, let SeedBytes: u32
     let compressed =
         std::hash::poseidon2::Poseidon2::hash(rolling_hash_fields, (SeedBytes / 31) + 1);
     let mut rolling_hash: [Field; 2] = [compressed, 0];
-    let num_hashes = (30 * N) / 32 + (((30 * N) % 32) != 0) as u32;
+
+    let num_hashes = (240 * N) / 254 + (((30 * N) % 32) != 0) as u32;
     for i in 0..num_hashes - 1 {
         let hash: Field = std::hash::poseidon2::Poseidon2::hash(rolling_hash, 2);
         let hash: [u8; 32] = hash.to_le_bytes();
@@ -73,6 +74,7 @@ pub(crate) fn derive_from_seed<let N: u32, let MOD_BITS: u32, let SeedBytes: u32
         }
         rolling_hash[1] += 1;
     }
+
     {
         let hash: Field = std::hash::poseidon2::Poseidon2::hash(rolling_hash, 2);
         let hash: [u8; 32] = hash.to_le_bytes();
@@ -267,7 +269,6 @@ pub(crate) fn validate_gt<let N: u32, let MOD_BITS: u32>(lhs: [Field; N], rhs: [
     // a - b = r
     // p + a - b - r = 0
     let (result, carry_flags, borrow_flags) = unsafe { __validate_gt_remainder(lhs, rhs) };
-
     validate_in_range::<_, MOD_BITS>(result);
 
     let borrow_shift = 0x1000000000000000000000000000000;
@@ -278,12 +279,14 @@ pub(crate) fn validate_gt<let N: u32, let MOD_BITS: u32>(lhs: [Field; N], rhs: [
         + (borrow_flags[0] as Field * borrow_shift)
         - (carry_flags[0] as Field * carry_shift);
     assert(result_limb == 0);
+
     for i in 1..N - 1 {
         let result_limb = lhs[i] - rhs[i] + addend[i] - result[i] - borrow_flags[i - 1] as Field
             + carry_flags[i - 1] as Field
             + ((borrow_flags[i] as Field - carry_flags[i] as Field) * borrow_shift);
         assert(result_limb == 0);
     }
+
     let result_limb = lhs[N - 1] - rhs[N - 1] + addend[N - 1]
         - result[N - 1]
         - borrow_flags[N - 2] as Field

diff --git a/src/fns/unconstrained_helpers.nr b/src/fns/unconstrained_helpers.nr
@@ -68,7 +68,6 @@ pub(crate) unconstrained fn __validate_gt_remainder<let N: u32>(
             borrow_flags[i / 2] = borrow as bool;
         }
     }
-
     let result = U60Repr::into(result_u60);
     (result, carry_flags, borrow_flags)
 }
@@ -204,12 +203,14 @@ pub(crate) unconstrained fn __barrett_reduction<let N: u32>(
     modulus: [Field; N],
     modulus_u60: U60Repr<N, 4>,
 ) -> ([Field; N], [Field; N]) {
+    // for each i in 0..(N + N), adds x[i] * redc_param[j] to mulout[i + j] for each j in 0..N
     let mut mulout: [Field; 3 * N] = [0; 3 * N];
     for i in 0..(N + N) {
         for j in 0..N {
             mulout[i + j] += x[i] * redc_param[j];
         }
     }
+
     mulout = split_bits::__normalize_limbs(mulout, 3 * N - 1);
     let mulout_u60: U60Repr<N, 6> = U60Repr::new(mulout);
 
@@ -255,13 +256,22 @@ pub(crate) unconstrained fn __barrett_reduction<let N: u32>(
     }
     let quotient_mul_modulus_u60: U60Repr<N, 4> = U60Repr::new(quotient_mul_modulus_normalized);
 
+    // convert the input into U60Repr
     let x_u60: U60Repr<N, 4> = U60Repr::new(x);
     let mut remainder_u60 = x_u60 - quotient_mul_modulus_u60;
-
+    // barrett reduction is quircky so might need to remove a few modulus_u60 from the remainder
     if (remainder_u60.gte(modulus_u60)) {
         remainder_u60 = remainder_u60 - modulus_u60;
         quotient_u60.increment();
     } else {}
+    if (remainder_u60.gte(modulus_u60)) {
+        remainder_u60 = remainder_u60 - modulus_u60;
+        quotient_u60.increment();
+    }
+    if (remainder_u60.gte(modulus_u60)) {
+        remainder_u60 = remainder_u60 - modulus_u60;
+        quotient_u60.increment();
+    }
 
     let q: [Field; N] = U60Repr::into(quotient_u60);
     let r: [Field; N] = U60Repr::into(remainder_u60);

diff --git a/src/fns/unconstrained_ops.nr b/src/fns/unconstrained_ops.nr
@@ -1,11 +1,11 @@
-use crate::utils::split_bits;
-use crate::utils::u60_representation::U60Repr;
-
+use crate::fns::constrained_ops::derive_from_seed;
 use crate::fns::unconstrained_helpers::{
     __barrett_reduction, __multiplicative_generator, __primitive_root_log_size,
     __tonelli_shanks_sqrt_inner_loop_check,
 };
 use crate::params::BigNumParams as P;
+use crate::utils::split_bits;
+use crate::utils::u60_representation::U60Repr;
 
 /**
  * In this file:
@@ -33,86 +33,24 @@ pub(crate) unconstrained fn __one<let N: u32>() -> [Field; N] {
     limbs
 }
 
+/// Deterministically derives a big_num from a seed value.
+///
+/// Takes a seed byte array and generates a big_num in the range [0, modulus-1].
+///
+/// ## Value Parameters
+///
+/// - `params`: The BigNum parameters containing modulus and reduction info
+/// - `seed`:  Input seed bytes to derive from.
+///
+/// ## Returns
+///
+///  An array of field elements derived from the seed (the limbs of the big_num)
 pub(crate) unconstrained fn __derive_from_seed<let N: u32, let MOD_BITS: u32, let SeedBytes: u32>(
     params: P<N, MOD_BITS>,
     seed: [u8; SeedBytes],
 ) -> [Field; N] {
-    let mut rolling_hash_fields: [Field; (SeedBytes / 31) + 1] = [0; (SeedBytes / 31) + 1];
-    let mut seed_ptr = 0;
-    for i in 0..(SeedBytes / 31) + 1 {
-        let mut packed: Field = 0;
-        for _ in 0..31 {
-            if (seed_ptr < SeedBytes) {
-                packed *= 256;
-                packed += seed[seed_ptr] as Field;
-                seed_ptr += 1;
-            }
-        }
-        rolling_hash_fields[i] = packed;
-    }
-    let compressed =
-        std::hash::poseidon2::Poseidon2::hash(rolling_hash_fields, (SeedBytes / 31) + 1);
-    let mut rolling_hash: [Field; 2] = [compressed, 0];
-
-    let mut to_reduce: [Field; 2 * N] = [0; 2 * N];
-
-    let mut double_modulus_bits = MOD_BITS * 2;
-    let mut double_modulus_bytes =
-        (double_modulus_bits) / 8 + (double_modulus_bits % 8 != 0) as u32;
-
-    let mut last_limb_bytes = double_modulus_bytes % 15;
-    if (last_limb_bytes == 0) {
-        last_limb_bytes = 15;
-    }
-    let mut last_limb_bits = double_modulus_bits % 8;
-    if (last_limb_bits == 0) {
-        last_limb_bits = 8;
-    }
-
-    for i in 0..(N - 1) {
-        let hash = std::hash::poseidon2::Poseidon2::hash(rolling_hash, 2);
-        let hash: [u8; 30] = hash.to_le_bytes();
-        let mut lo: Field = 0;
-        let mut hi: Field = 0;
-        for j in 0..15 {
-            hi *= 256;
-            lo *= 256;
-
-            if (i < 2 * N - 2) {
-                lo += hash[j + 15] as Field;
-                hi += hash[j] as Field;
-            }
-        }
-        to_reduce[2 * i] = lo;
-        to_reduce[2 * i + 1] = hi;
-        rolling_hash[1] += 1;
-    }
-
-    {
-        let hash = std::hash::poseidon2::Poseidon2::hash(rolling_hash, 2);
-        let hash: [u8; 30] = hash.to_le_bytes();
-        let mut hi: Field = 0;
-        for j in 0..(last_limb_bytes - 1) {
-            hi *= 256;
-            hi += hash[j] as Field;
-        }
-        hi *= 256;
-        let last_byte = hash[last_limb_bytes - 1];
-        let mask = (1 as u64 << (last_limb_bits) as u8) - 1;
-        let last_bits = last_byte as u64 & mask;
-        hi += last_bits as Field;
-        to_reduce[2 * N - 2] = hi;
-    }
-
-    let (_, remainder) = __barrett_reduction(
-        to_reduce,
-        params.redc_param,
-        MOD_BITS,
-        params.modulus,
-        params.modulus_u60_x4,
-    );
-    let result = remainder;
-    result
+    let out = derive_from_seed::<N, MOD_BITS, SeedBytes>(params, seed);
+    out
 }
 
 pub(crate) unconstrained fn __eq<let N: u32>(lhs: [Field; N], rhs: [Field; N]) -> bool {
@@ -124,6 +62,7 @@ pub(crate) unconstrained fn __is_zero<let N: u32>(limbs: [Field; N]) -> bool {
     for i in 0..N {
         result = result & (limbs[i] == 0);
     }
+
     result
 }
 

diff --git a/src/tests/bignum_test.nr b/src/tests/bignum_test.nr
@@ -624,7 +624,6 @@ type U256 = BN256;
 fn test_udiv_mod_U256() {
     let a: U256 = unsafe { BigNum::__derive_from_seed([1, 2, 3, 4]) };
     let b: U256 = BigNum::from_array([12, 0, 0]);
-
     let (q, r) = a.udiv_mod(b);
 
     // let qb = q.__mul(b);