refactor: updating field conversion code without pointer hack (#4537)

We currently use a pointer hack for functions like `calc_num_bn254_frs` and `convert_from_bn254_frs`. This PR aims to clean these up using traits and template metaprogramming. Also closes AztecProtocol/barretenberg#846, by just sending and receiving an std::array instead of an AllValues object.
AztecProtocol · Feb 12, 2024 · 94f436e · 94f436e
1 parent 6e89d53
commit 94f436e
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diff --git a/barretenberg/cpp/src/barretenberg/ecc/curves/bn254/fq.hpp b/barretenberg/cpp/src/barretenberg/ecc/curves/bn254/fq.hpp
@@ -60,6 +60,9 @@ class Bn254FqParams {
     // used in msgpack schema serialization
     static constexpr char schema_name[] = "fq";
     static constexpr bool has_high_2adicity = false;
+
+    // The modulus is larger than BN254 scalar field modulus, so it maps to two BN254 scalars
+    static constexpr size_t NUM_BN254_SCALARS = 2;
 };
 
 using fq = field<Bn254FqParams>;

diff --git a/barretenberg/cpp/src/barretenberg/ecc/curves/bn254/fr.hpp b/barretenberg/cpp/src/barretenberg/ecc/curves/bn254/fr.hpp
@@ -66,6 +66,9 @@ class Bn254FrParams {
     // used in msgpack schema serialization
     static constexpr char schema_name[] = "fr";
     static constexpr bool has_high_2adicity = true;
+
+    // This is a BN254 scalar, so it represents one BN254 scalar
+    static constexpr size_t NUM_BN254_SCALARS = 1;
 };
 
 using fr = field<Bn254FrParams>;

diff --git a/barretenberg/cpp/src/barretenberg/ecc/fields/field_conversion.cpp b/barretenberg/cpp/src/barretenberg/ecc/fields/field_conversion.cpp
@@ -7,18 +7,6 @@ namespace bb::field_conversion {
 static constexpr uint64_t NUM_LIMB_BITS = plonk::NUM_LIMB_BITS_IN_FIELD_SIMULATION;
 static constexpr uint64_t TOTAL_BITS = 254;
 
-bb::fr convert_from_bn254_frs(std::span<const bb::fr> fr_vec, bb::fr* /*unused*/)
-{
-    ASSERT(fr_vec.size() == 1);
-    return fr_vec[0];
-}
-
-bool convert_from_bn254_frs(std::span<const bb::fr> fr_vec, bool* /*unused*/)
-{
-    ASSERT(fr_vec.size() == 1);
-    return fr_vec[0] != 0;
-}
-
 /**
  * @brief Converts 2 bb::fr elements to grumpkin::fr
  * @details First, this function must take in 2 bb::fr elements because the grumpkin::fr field has a larger modulus than
@@ -32,7 +20,7 @@ bool convert_from_bn254_frs(std::span<const bb::fr> fr_vec, bool* /*unused*/)
  * @param high_bits_in
  * @return grumpkin::fr
  */
-grumpkin::fr convert_from_bn254_frs(std::span<const bb::fr> fr_vec, grumpkin::fr* /*unused*/)
+grumpkin::fr convert_grumpkin_fr_from_bn254_frs(std::span<const bb::fr> fr_vec)
 {
     // Combines the two elements into one uint256_t, and then convert that to a grumpkin::fr
     ASSERT(uint256_t(fr_vec[0]) < (uint256_t(1) << (NUM_LIMB_BITS * 2)));              // lower 136 bits
@@ -42,25 +30,6 @@ grumpkin::fr convert_from_bn254_frs(std::span<const bb::fr> fr_vec, grumpkin::fr
     return result;
 }
 
-curve::BN254::AffineElement convert_from_bn254_frs(std::span<const bb::fr> fr_vec,
-                                                   curve::BN254::AffineElement* /*unused*/)
-{
-    curve::BN254::AffineElement val;
-    val.x = convert_from_bn254_frs<grumpkin::fr>(fr_vec.subspan(0, 2));
-    val.y = convert_from_bn254_frs<grumpkin::fr>(fr_vec.subspan(2, 2));
-    return val;
-}
-
-curve::Grumpkin::AffineElement convert_from_bn254_frs(std::span<const bb::fr> fr_vec,
-                                                      curve::Grumpkin::AffineElement* /*unused*/)
-{
-    ASSERT(fr_vec.size() == 2);
-    curve::Grumpkin::AffineElement val;
-    val.x = fr_vec[0];
-    val.y = fr_vec[1];
-    return val;
-}
-
 /**
  * @brief Converts grumpkin::fr to 2 bb::fr elements
  * @details First, this function must return 2 bb::fr elements because the grumpkin::fr field has a larger modulus than
@@ -74,7 +43,7 @@ curve::Grumpkin::AffineElement convert_from_bn254_frs(std::span<const bb::fr> fr
  * @param input
  * @return std::array<bb::fr, 2>
  */
-std::vector<bb::fr> convert_to_bn254_frs(const grumpkin::fr& val)
+std::vector<bb::fr> convert_grumpkin_fr_to_bn254_frs(const grumpkin::fr& val)
 {
     // Goal is to slice up the 64 bit limbs of grumpkin::fr/uint256_t to mirror the 68 bit limbs of bigfield
     // We accomplish this by dividing the grumpkin::fr's value into two 68*2=136 bit pieces.
@@ -89,30 +58,6 @@ std::vector<bb::fr> convert_to_bn254_frs(const grumpkin::fr& val)
     return result;
 }
 
-std::vector<bb::fr> convert_to_bn254_frs(const bb::fr& val)
-{
-    std::vector<bb::fr> fr_vec{ val };
-    return fr_vec;
-}
-
-std::vector<bb::fr> convert_to_bn254_frs(const curve::BN254::AffineElement& val)
-{
-    auto fr_vec_x = convert_to_bn254_frs(val.x);
-    auto fr_vec_y = convert_to_bn254_frs(val.y);
-    std::vector<bb::fr> fr_vec(fr_vec_x.begin(), fr_vec_x.end());
-    fr_vec.insert(fr_vec.end(), fr_vec_y.begin(), fr_vec_y.end());
-    return fr_vec;
-}
-
-std::vector<bb::fr> convert_to_bn254_frs(const curve::Grumpkin::AffineElement& val)
-{
-    auto fr_vec_x = convert_to_bn254_frs(val.x);
-    auto fr_vec_y = convert_to_bn254_frs(val.y);
-    std::vector<bb::fr> fr_vec(fr_vec_x.begin(), fr_vec_x.end());
-    fr_vec.insert(fr_vec.end(), fr_vec_y.begin(), fr_vec_y.end());
-    return fr_vec;
-}
-
 grumpkin::fr convert_to_grumpkin_fr(const bb::fr& f)
 {
     const uint64_t NUM_BITS_IN_TWO_LIMBS = 2 * NUM_LIMB_BITS; // the number of bits in 2 bigfield limbs which is 136

diff --git a/barretenberg/cpp/src/barretenberg/ecc/fields/field_conversion.hpp b/barretenberg/cpp/src/barretenberg/ecc/fields/field_conversion.hpp
@@ -4,6 +4,7 @@
 #include "barretenberg/ecc/curves/bn254/fr.hpp"
 #include "barretenberg/ecc/curves/grumpkin/grumpkin.hpp"
 #include "barretenberg/polynomials/univariate.hpp"
+#include "barretenberg/proof_system/types/circuit_type.hpp"
 
 namespace bb::field_conversion {
 
@@ -15,48 +16,22 @@ namespace bb::field_conversion {
  * @tparam T
  * @return constexpr size_t
  */
-template <typename T> constexpr size_t calc_num_bn254_frs();
-
-constexpr size_t calc_num_bn254_frs(bb::fr* /*unused*/)
-{
-    return 1;
-}
-
-constexpr size_t calc_num_bn254_frs(grumpkin::fr* /*unused*/)
-{
-    return 2;
-}
-
-template <std::integral T> constexpr size_t calc_num_bn254_frs(T* /*unused*/)
-{
-    return 1; // meant for integral types that are less than 254 bits
-}
-
-constexpr size_t calc_num_bn254_frs(curve::BN254::AffineElement* /*unused*/)
-{
-    return 2 * calc_num_bn254_frs<curve::BN254::BaseField>();
-}
-
-constexpr size_t calc_num_bn254_frs(curve::Grumpkin::AffineElement* /*unused*/)
-{
-    return 2 * calc_num_bn254_frs<curve::Grumpkin::BaseField>();
-}
-
-template <typename T, std::size_t N> constexpr size_t calc_num_bn254_frs(std::array<T, N>* /*unused*/)
-{
-    return N * calc_num_bn254_frs<T>();
-}
-
-template <typename T, std::size_t N> constexpr size_t calc_num_bn254_frs(bb::Univariate<T, N>* /*unused*/)
-{
-    return N * calc_num_bn254_frs<T>();
-}
-
 template <typename T> constexpr size_t calc_num_bn254_frs()
 {
-    return calc_num_bn254_frs(static_cast<T*>(nullptr));
+    if constexpr (IsAnyOf<T, uint32_t, bool>) {
+        return 1;
+    } else if constexpr (IsAnyOf<T, bb::fr, grumpkin::fr>) {
+        return T::Params::NUM_BN254_SCALARS;
+    } else if constexpr (IsAnyOf<T, curve::BN254::AffineElement, curve::Grumpkin::AffineElement>) {
+        return 2 * calc_num_bn254_frs<typename T::Fq>();
+    } else {
+        // Array or Univariate
+        return calc_num_bn254_frs<typename T::value_type>() * (std::tuple_size<T>::value);
+    }
 }
 
+grumpkin::fr convert_grumpkin_fr_from_bn254_frs(std::span<const bb::fr> fr_vec);
+
 /**
  * @brief Conversions from vector of bb::fr elements to transcript types.
  * @details We want to support the following types: bool, size_t, uint32_t, uint64_t, bb::fr, grumpkin::fr,
@@ -68,75 +43,40 @@ template <typename T> constexpr size_t calc_num_bn254_frs()
  * @param fr_vec
  * @return T
  */
-template <typename T> T convert_from_bn254_frs(std::span<const bb::fr> fr_vec);
-
-bool convert_from_bn254_frs(std::span<const bb::fr> fr_vec, bool* /*unused*/);
-
-template <std::integral T> inline T convert_from_bn254_frs(std::span<const bb::fr> fr_vec, T* /*unused*/)
-{
-    ASSERT(fr_vec.size() == 1);
-    return static_cast<T>(fr_vec[0]);
-}
-
-bb::fr convert_from_bn254_frs(std::span<const bb::fr> fr_vec, bb::fr* /*unused*/);
-
-grumpkin::fr convert_from_bn254_frs(std::span<const bb::fr> fr_vec, grumpkin::fr* /*unused*/);
-
-curve::BN254::AffineElement convert_from_bn254_frs(std::span<const bb::fr> fr_vec,
-                                                   curve::BN254::AffineElement* /*unused*/);
-
-curve::Grumpkin::AffineElement convert_from_bn254_frs(std::span<const bb::fr> fr_vec,
-                                                      curve::Grumpkin::AffineElement* /*unused*/);
-
-template <size_t N>
-inline std::array<bb::fr, N> convert_from_bn254_frs(std::span<const bb::fr> fr_vec, std::array<bb::fr, N>* /*unused*/)
-{
-    std::array<bb::fr, N> val;
-    for (size_t i = 0; i < N; ++i) {
-        val[i] = fr_vec[i];
-    }
-    return val;
-}
-
-template <size_t N>
-inline std::array<grumpkin::fr, N> convert_from_bn254_frs(std::span<const bb::fr> fr_vec,
-                                                          std::array<grumpkin::fr, N>* /*unused*/)
-{
-    std::array<grumpkin::fr, N> val;
-    for (size_t i = 0; i < N; ++i) {
-        std::vector<bb::fr> fr_vec_tmp{ fr_vec[2 * i],
-                                        fr_vec[2 * i + 1] }; // each pair of consecutive elements is a grumpkin::fr
-        val[i] = convert_from_bn254_frs<grumpkin::fr>(fr_vec_tmp);
-    }
-    return val;
-}
-
-template <size_t N>
-inline Univariate<bb::fr, N> convert_from_bn254_frs(std::span<const bb::fr> fr_vec, Univariate<bb::fr, N>* /*unused*/)
-{
-    Univariate<bb::fr, N> val;
-    for (size_t i = 0; i < N; ++i) {
-        val.evaluations[i] = fr_vec[i];
-    }
-    return val;
-}
-
-template <size_t N>
-inline Univariate<grumpkin::fr, N> convert_from_bn254_frs(std::span<const bb::fr> fr_vec,
-                                                          Univariate<grumpkin::fr, N>* /*unused*/)
+template <typename T> T convert_from_bn254_frs(std::span<const bb::fr> fr_vec)
 {
-    Univariate<grumpkin::fr, N> val;
-    for (size_t i = 0; i < N; ++i) {
-        std::vector<bb::fr> fr_vec_tmp{ fr_vec[2 * i], fr_vec[2 * i + 1] };
-        val.evaluations[i] = convert_from_bn254_frs<grumpkin::fr>(fr_vec_tmp);
+    if constexpr (IsAnyOf<T, bool>) {
+        ASSERT(fr_vec.size() == 1);
+        return bool(fr_vec[0]);
+    } else if constexpr (IsAnyOf<T, uint32_t, bb::fr>) {
+        ASSERT(fr_vec.size() == 1);
+        return static_cast<T>(fr_vec[0]);
+    } else if constexpr (IsAnyOf<T, grumpkin::fr>) {
+        ASSERT(fr_vec.size() == 2);
+        return convert_grumpkin_fr_from_bn254_frs(fr_vec);
+    } else if constexpr (IsAnyOf<T, curve::BN254::AffineElement, curve::Grumpkin::AffineElement>) {
+        using BaseField = typename T::Fq;
+        constexpr size_t BASE_FIELD_SCALAR_SIZE = calc_num_bn254_frs<BaseField>();
+        ASSERT(fr_vec.size() == 2 * BASE_FIELD_SCALAR_SIZE);
+        T val;
+        val.x = convert_from_bn254_frs<BaseField>(fr_vec.subspan(0, BASE_FIELD_SCALAR_SIZE));
+        val.y = convert_from_bn254_frs<BaseField>(fr_vec.subspan(BASE_FIELD_SCALAR_SIZE, BASE_FIELD_SCALAR_SIZE));
+        return val;
+    } else {
+        // Array or Univariate
+        T val;
+        constexpr size_t FieldScalarSize = calc_num_bn254_frs<typename T::value_type>();
+        ASSERT(fr_vec.size() == FieldScalarSize * std::tuple_size<T>::value);
+        size_t i = 0;
+        for (auto& x : val) {
+            x = convert_from_bn254_frs<typename T::value_type>(fr_vec.subspan(FieldScalarSize * i, FieldScalarSize));
+            ++i;
+        }
+        return val;
     }
-    return val;
 }
 
-template <typename T> T convert_from_bn254_frs(std::span<const bb::fr> fr_vec)
-{
-    return convert_from_bn254_frs(fr_vec, static_cast<T*>(nullptr));
-}
+std::vector<bb::fr> convert_grumpkin_fr_to_bn254_frs(const grumpkin::fr& val);
 
 /**
  * @brief Conversion from transcript values to bb::frs
@@ -147,65 +87,28 @@ template <typename T> T convert_from_bn254_frs(std::span<const bb::fr> fr_vec)
  * @param val
  * @return std::vector<bb::fr>
  */
-template <std::integral T> std::vector<bb::fr> inline convert_to_bn254_frs(const T& val)
-{
-    std::vector<bb::fr> fr_vec{ val };
-    return fr_vec;
-}
-
-std::vector<bb::fr> convert_to_bn254_frs(const grumpkin::fr& val);
-
-std::vector<bb::fr> convert_to_bn254_frs(const bb::fr& val);
-
-std::vector<bb::fr> convert_to_bn254_frs(const curve::BN254::AffineElement& val);
-
-std::vector<bb::fr> convert_to_bn254_frs(const curve::Grumpkin::AffineElement& val);
-
-template <size_t N> std::vector<bb::fr> inline convert_to_bn254_frs(const std::array<bb::fr, N>& val)
-{
-    std::vector<bb::fr> fr_vec(val.begin(), val.end());
-    return fr_vec;
-}
-
-template <size_t N> std::vector<bb::fr> inline convert_to_bn254_frs(const std::array<grumpkin::fr, N>& val)
-{
-    std::vector<bb::fr> fr_vec;
-    for (size_t i = 0; i < N; ++i) {
-        auto tmp_vec = convert_to_bn254_frs(val[i]);
-        fr_vec.insert(fr_vec.end(), tmp_vec.begin(), tmp_vec.end());
-    }
-    return fr_vec;
-}
-
-template <size_t N> std::vector<bb::fr> inline convert_to_bn254_frs(const bb::Univariate<bb::fr, N>& val)
-{
-    std::vector<bb::fr> fr_vec;
-    for (size_t i = 0; i < N; ++i) {
-        auto tmp_vec = convert_to_bn254_frs(val.evaluations[i]);
-        fr_vec.insert(fr_vec.end(), tmp_vec.begin(), tmp_vec.end());
-    }
-    return fr_vec;
-}
-
-template <size_t N> std::vector<bb::fr> inline convert_to_bn254_frs(const bb::Univariate<grumpkin::fr, N>& val)
-{
-    std::vector<bb::fr> fr_vec;
-    for (size_t i = 0; i < N; ++i) {
-        auto tmp_vec = convert_to_bn254_frs(val.evaluations[i]);
-        fr_vec.insert(fr_vec.end(), tmp_vec.begin(), tmp_vec.end());
-    }
-    return fr_vec;
-}
-
-template <typename AllValues> std::vector<bb::fr> inline convert_to_bn254_frs(const AllValues& val)
-{
-    auto data = val.get_all();
-    std::vector<bb::fr> fr_vec;
-    for (auto& item : data) {
-        auto tmp_vec = convert_to_bn254_frs(item);
-        fr_vec.insert(fr_vec.end(), tmp_vec.begin(), tmp_vec.end());
+template <typename T> std::vector<bb::fr> convert_to_bn254_frs(const T& val)
+{
+    if constexpr (IsAnyOf<T, bool, uint32_t, bb::fr>) {
+        std::vector<bb::fr> fr_vec{ val };
+        return fr_vec;
+    } else if constexpr (IsAnyOf<T, grumpkin::fr>) {
+        return convert_grumpkin_fr_to_bn254_frs(val);
+    } else if constexpr (IsAnyOf<T, curve::BN254::AffineElement, curve::Grumpkin::AffineElement>) {
+        auto fr_vec_x = convert_to_bn254_frs(val.x);
+        auto fr_vec_y = convert_to_bn254_frs(val.y);
+        std::vector<bb::fr> fr_vec(fr_vec_x.begin(), fr_vec_x.end());
+        fr_vec.insert(fr_vec.end(), fr_vec_y.begin(), fr_vec_y.end());
+        return fr_vec;
+    } else {
+        // Array or Univariate
+        std::vector<bb::fr> fr_vec;
+        for (auto& x : val) {
+            auto tmp_vec = convert_to_bn254_frs(x);
+            fr_vec.insert(fr_vec.end(), tmp_vec.begin(), tmp_vec.end());
+        }
+        return fr_vec;
     }
-    return fr_vec;
 }
 
 grumpkin::fr convert_to_grumpkin_fr(const bb::fr& f);

diff --git a/barretenberg/cpp/src/barretenberg/ecc/groups/affine_element.hpp b/barretenberg/cpp/src/barretenberg/ecc/groups/affine_element.hpp
@@ -8,8 +8,11 @@
 namespace bb::group_elements {
 template <typename T>
 concept SupportsHashToCurve = T::can_hash_to_curve;
-template <typename Fq, typename Fr, typename Params> class alignas(64) affine_element {
+template <typename Fq_, typename Fr_, typename Params> class alignas(64) affine_element {
   public:
+    using Fq = Fq_;
+    using Fr = Fr_;
+
     using in_buf = const uint8_t*;
     using vec_in_buf = const uint8_t*;
     using out_buf = uint8_t*;