polynomial.cpp

Go to the documentation of this file.

// === AUDIT STATUS ===
// internal:    { status: not started, auditors: [], date: YYYY-MM-DD }
// external_1:  { status: not started, auditors: [], date: YYYY-MM-DD }
// external_2:  { status: not started, auditors: [], date: YYYY-MM-DD }
// =====================
 
#include "polynomial.hpp"
#include "barretenberg/common/assert.hpp"
#include "barretenberg/common/bb_bench.hpp"
#include "barretenberg/common/slab_allocator.hpp"
#include "barretenberg/common/thread.hpp"
#include "barretenberg/numeric/bitop/get_msb.hpp"
#include "barretenberg/numeric/bitop/pow.hpp"
#include "barretenberg/polynomials/backing_memory.hpp"
#include "barretenberg/polynomials/shared_shifted_virtual_zeroes_array.hpp"
#include "polynomial_arithmetic.hpp"
#include <cstddef>
#include <fcntl.h>
#include <list>
#include <memory>
#include <mutex>
#include <span>
#include <sys/stat.h>
#include <unordered_map>
#include <utility>
 
namespace bb {
 
// Note: This function is pretty gnarly, but we try to make it the only function that deals
// with copying polynomials. It should be scrutinized thusly.
template <typename Fr>
SharedShiftedVirtualZeroesArray<Fr> _clone(const SharedShiftedVirtualZeroesArray<Fr>& array,
                                           size_t right_expansion = 0,
                                           size_t left_expansion = 0)
{
    size_t expanded_size = array.size() + right_expansion + left_expansion;
    BackingMemory<Fr> backing_clone = BackingMemory<Fr>::allocate(expanded_size);
    // zero any left extensions to the array
    memset(static_cast<void*>(backing_clone.raw_data), 0, sizeof(Fr) * left_expansion);
    // copy our cloned array over
    memcpy(static_cast<void*>(backing_clone.raw_data + left_expansion),
           static_cast<const void*>(array.data()),
           sizeof(Fr) * array.size());
    // zero any right extensions to the array
    memset(static_cast<void*>(backing_clone.raw_data + left_expansion + array.size()), 0, sizeof(Fr) * right_expansion);
    return {
        array.start_ - left_expansion, array.end_ + right_expansion, array.virtual_size_, std::move(backing_clone)
    };
}
 
template <typename Fr>
void Polynomial<Fr>::allocate_backing_memory(size_t size, size_t virtual_size, size_t start_index)
{
    BB_BENCH_NAME("Polynomial::allocate_backing_memory");
    BB_ASSERT_LTE(start_index + size, virtual_size);
    coefficients_ = SharedShiftedVirtualZeroesArray<Fr>{
        start_index,        /* start index, used for shifted polynomials and offset 'islands' of non-zeroes */
        size + start_index, /* end index, actual memory used is (end - start) */
        virtual_size,       /* virtual size, i.e. until what size do we conceptually have zeroes */
        BackingMemory<Fr>::allocate(size)
    };
}
 
template <typename Fr> Polynomial<Fr>::Polynomial(size_t size, size_t virtual_size, size_t start_index)
{
    BB_BENCH_NAME("Polynomial::Polynomial(size_t, size_t, size_t)");
    allocate_backing_memory(size, virtual_size, start_index);
 
    size_t num_threads = calculate_num_threads(size);
    size_t range_per_thread = size / num_threads;
    size_t leftovers = size - (range_per_thread * num_threads);
 
    parallel_for(num_threads, [&](size_t j) {
        size_t offset = j * range_per_thread;
        size_t range = (j == num_threads - 1) ? range_per_thread + leftovers : range_per_thread;
        ASSERT(offset < size || size == 0);
        BB_ASSERT_LTE((offset + range), size);
        memset(static_cast<void*>(coefficients_.data() + offset), 0, sizeof(Fr) * range);
    });
}
 
template <typename Fr>
Polynomial<Fr>::Polynomial(size_t size, size_t virtual_size, size_t start_index, [[maybe_unused]] DontZeroMemory flag)
{
    allocate_backing_memory(size, virtual_size, start_index);
}
 
template <typename Fr>
Polynomial<Fr>::Polynomial(const Polynomial<Fr>& other)
    : Polynomial<Fr>(other, other.size())
{}
 
// fully copying "expensive" constructor
template <typename Fr> Polynomial<Fr>::Polynomial(const Polynomial<Fr>& other, const size_t target_size)
{
    BB_ASSERT_LTE(other.size(), target_size);
    coefficients_ = _clone(other.coefficients_, target_size - other.size());
}
 
// interpolation constructor
template <typename Fr>
Polynomial<Fr>::Polynomial(std::span<const Fr> interpolation_points,
                           std::span<const Fr> evaluations,
                           size_t virtual_size)
    : Polynomial(interpolation_points.size(), virtual_size)
{
    BB_ASSERT_GT(coefficients_.size(), static_cast<size_t>(0));
 
    polynomial_arithmetic::compute_efficient_interpolation(
        evaluations.data(), coefficients_.data(), interpolation_points.data(), coefficients_.size());
}
 
template <typename Fr> Polynomial<Fr>::Polynomial(std::span<const Fr> coefficients, size_t virtual_size)
{
    allocate_backing_memory(coefficients.size(), virtual_size, 0);
 
    memcpy(static_cast<void*>(data()), static_cast<const void*>(coefficients.data()), sizeof(Fr) * coefficients.size());
}
 
// Assignments
 
// full copy "expensive" assignment
template <typename Fr> Polynomial<Fr>& Polynomial<Fr>::operator=(const Polynomial<Fr>& other)
{
    if (this == &other) {
        return *this;
    }
    coefficients_ = _clone(other.coefficients_);
    return *this;
}
 
template <typename Fr> Polynomial<Fr> Polynomial<Fr>::share() const
{
    Polynomial p;
    p.coefficients_ = coefficients_;
    return p;
}
 
template <typename Fr> bool Polynomial<Fr>::operator==(Polynomial const& rhs) const
{
    // If either is empty, both must be
    if (is_empty() || rhs.is_empty()) {
        return is_empty() && rhs.is_empty();
    }
    // Size must agree
    if (virtual_size() != rhs.virtual_size()) {
        return false;
    }
    // Each coefficient must agree
    for (size_t i = std::min(coefficients_.start_, rhs.coefficients_.start_);
         i < std::max(coefficients_.end_, rhs.coefficients_.end_);
         i++) {
        if (coefficients_.get(i) != rhs.coefficients_.get(i)) {
            return false;
        }
    }
    return true;
}
 
template <typename Fr> Polynomial<Fr>& Polynomial<Fr>::operator+=(PolynomialSpan<const Fr> other)
{
    BB_ASSERT_LTE(start_index(), other.start_index);
    BB_ASSERT_GTE(end_index(), other.end_index());
    size_t num_threads = calculate_num_threads(other.size());
    size_t range_per_thread = other.size() / num_threads;
    size_t leftovers = other.size() - (range_per_thread * num_threads);
    parallel_for(num_threads, [&](size_t j) {
        size_t offset = j * range_per_thread + other.start_index;
        size_t end = (j == num_threads - 1) ? offset + range_per_thread + leftovers : offset + range_per_thread;
        for (size_t i = offset; i < end; ++i) {
            at(i) += other[i];
        }
    });
    return *this;
}
 
template <typename Fr> Fr Polynomial<Fr>::evaluate(const Fr& z, const size_t target_size) const
{
    ASSERT(size() == virtual_size());
    return polynomial_arithmetic::evaluate(data(), z, target_size);
}
 
template <typename Fr> Fr Polynomial<Fr>::evaluate(const Fr& z) const
{
    ASSERT(size() == virtual_size());
    return polynomial_arithmetic::evaluate(data(), z, size());
}
 
template <typename Fr> Fr Polynomial<Fr>::evaluate_mle(std::span<const Fr> evaluation_points, bool shift) const
{
    return _evaluate_mle(evaluation_points, coefficients_, shift);
}
 
template <typename Fr> Polynomial<Fr> Polynomial<Fr>::partial_evaluate_mle(std::span<const Fr> evaluation_points) const
{
    // Get size of partial evaluation point u = (u_0,...,u_{m-1})
    const size_t m = evaluation_points.size();
 
    // Assert that the size of the Polynomial being evaluated is a power of 2 greater than (1 << m)
    ASSERT(numeric::is_power_of_two(size()));
    BB_ASSERT_GTE(size(), static_cast<size_t>(1 << m));
    size_t n = numeric::get_msb(size());
 
    // Partial evaluation is done in m rounds l = 0,...,m-1. At the end of round l, the Polynomial has been
    // partially evaluated at u_{m-l-1}, ..., u_{m-1} in variables X_{n-l-1}, ..., X_{n-1}. The size of this
    // Polynomial is n_l.
    size_t n_l = 1 << (n - 1);
 
    // Temporary buffer of half the size of the Polynomial
    Polynomial<Fr> intermediate(n_l, n_l, DontZeroMemory::FLAG);
 
    // Evaluate variable X_{n-1} at u_{m-1}
    Fr u_l = evaluation_points[m - 1];
 
    for (size_t i = 0; i < n_l; i++) {
        // Initiate our intermediate results using this Polynomial.
        intermediate.at(i) = get(i) + u_l * (get(i + n_l) - get(i));
    }
    // Evaluate m-1 variables X_{n-l-1}, ..., X_{n-2} at m-1 remaining values u_0,...,u_{m-2})
    for (size_t l = 1; l < m; ++l) {
        n_l = 1 << (n - l - 1);
        u_l = evaluation_points[m - l - 1];
        for (size_t i = 0; i < n_l; ++i) {
            intermediate.at(i) = intermediate[i] + u_l * (intermediate[i + n_l] - intermediate[i]);
        }
    }
 
    // Construct resulting Polynomial g(X_0,…,X_{n-m-1})) = p(X_0,…,X_{n-m-1},u_0,...u_{m-1}) from buffer
    Polynomial<Fr> result(n_l, n_l, DontZeroMemory::FLAG);
    for (size_t idx = 0; idx < n_l; ++idx) {
        result.at(idx) = intermediate[idx];
    }
 
    return result;
}
 
template <typename Fr>
Fr Polynomial<Fr>::compute_kate_opening_coefficients(const Fr& z)
    requires polynomial_arithmetic::SupportsFFT<Fr>
{
    return polynomial_arithmetic::compute_kate_opening_coefficients(data(), data(), z, size());
}
 
template <typename Fr>
Fr Polynomial<Fr>::compute_barycentric_evaluation(const Fr& z, const EvaluationDomain<Fr>& domain)
    requires polynomial_arithmetic::SupportsFFT<Fr>
{
    return polynomial_arithmetic::compute_barycentric_evaluation(data(), domain.size, z, domain);
}
 
template <typename Fr> Polynomial<Fr>& Polynomial<Fr>::operator-=(PolynomialSpan<const Fr> other)
{
    BB_ASSERT_LTE(start_index(), other.start_index);
    BB_ASSERT_GTE(end_index(), other.end_index());
    const size_t num_threads = calculate_num_threads(other.size());
    const size_t range_per_thread = other.size() / num_threads;
    const size_t leftovers = other.size() - (range_per_thread * num_threads);
    parallel_for(num_threads, [&](size_t j) {
        const size_t offset = j * range_per_thread + other.start_index;
        const size_t end = (j == num_threads - 1) ? offset + range_per_thread + leftovers : offset + range_per_thread;
        for (size_t i = offset; i < end; ++i) {
            at(i) -= other[i];
        }
    });
    return *this;
}
 
template <typename Fr> Polynomial<Fr>& Polynomial<Fr>::operator*=(const Fr scaling_factor)
{
    parallel_for([scaling_factor, this](const ThreadChunk& chunk) { multiply_chunk(chunk, scaling_factor); });
    return *this;
}
 
template <typename Fr> void Polynomial<Fr>::multiply_chunk(const ThreadChunk& chunk, const Fr scaling_factor)
{
    for (size_t i : chunk.range(size())) {
        data()[i] *= scaling_factor;
    }
}
 
template <typename Fr> Polynomial<Fr> Polynomial<Fr>::create_non_parallel_zero_init(size_t size, size_t virtual_size)
{
    Polynomial p(size, virtual_size, Polynomial<Fr>::DontZeroMemory::FLAG);
    memset(static_cast<void*>(p.coefficients_.data()), 0, sizeof(Fr) * size);
    return p;
}
 
// TODO(https://github.com/AztecProtocol/barretenberg/issues/1113): Optimizing based on actual sizes would involve using
// expand, but it is currently unused.
template <typename Fr>
Polynomial<Fr> Polynomial<Fr>::expand(const size_t new_start_index, const size_t new_end_index) const
{
    BB_ASSERT_LTE(new_end_index, virtual_size());
    BB_ASSERT_LTE(new_start_index, start_index());
    BB_ASSERT_GTE(new_end_index, end_index());
    if (new_start_index == start_index() && new_end_index == end_index()) {
        return *this;
    }
    Polynomial result = *this;
    // Make new_start_index..new_end_index usable
    result.coefficients_ = _clone(coefficients_, new_end_index - end_index(), start_index() - new_start_index);
    return result;
}
 
template <typename Fr> void Polynomial<Fr>::shrink_end_index(const size_t new_end_index)
{
    BB_ASSERT_LTE(new_end_index, end_index());
    coefficients_.end_ = new_end_index;
}
 
template <typename Fr> Polynomial<Fr> Polynomial<Fr>::full() const
{
    Polynomial result = *this;
    // Make 0..virtual_size usable
    result.coefficients_ = _clone(coefficients_, virtual_size() - end_index(), start_index());
    return result;
}
 
template <typename Fr> void Polynomial<Fr>::add_scaled(PolynomialSpan<const Fr> other, Fr scaling_factor) &
{
    BB_ASSERT_LTE(start_index(), other.start_index);
    BB_ASSERT_GTE(end_index(), other.end_index());
    parallel_for(
        [&other, scaling_factor, this](const ThreadChunk& chunk) { add_scaled_chunk(chunk, other, scaling_factor); });
}
 
template <typename Fr>
void Polynomial<Fr>::add_scaled_chunk(const ThreadChunk& chunk, PolynomialSpan<const Fr> other, Fr scaling_factor) &
{
    // Iterate over the chunk of the other polynomial's range
    for (size_t offset : chunk.range(other.size())) {
        size_t index = other.start_index + offset;
        at(index) += scaling_factor * other[index];
    }
}
 
template <typename Fr> Polynomial<Fr> Polynomial<Fr>::shifted() const
{
    BB_ASSERT_GTE(coefficients_.start_, static_cast<size_t>(1));
    Polynomial result;
    result.coefficients_ = coefficients_;
    result.coefficients_.start_ -= 1;
    result.coefficients_.end_ -= 1;
    return result;
}
 
template <typename Fr> Polynomial<Fr> Polynomial<Fr>::right_shifted(const size_t magnitude) const
{
    // ensure that at least the last magnitude-many coefficients are virtual 0's
    BB_ASSERT_LTE((coefficients_.end_ + magnitude), virtual_size());
    Polynomial result;
    result.coefficients_ = coefficients_;
    result.coefficients_.start_ += magnitude;
    result.coefficients_.end_ += magnitude;
    return result;
}
 
template <typename Fr> Polynomial<Fr> Polynomial<Fr>::reverse() const
{
    const size_t end_index = this->end_index();
    const size_t start_index = this->start_index();
    const size_t poly_size = this->size();
    Polynomial reversed(/*size=*/poly_size, /*virtual_size=*/end_index);
    for (size_t idx = end_index; idx > start_index; --idx) {
        reversed.at(end_index - idx) = this->at(idx - 1);
    }
    return reversed;
}
 
template class Polynomial<bb::fr>;
template class Polynomial<grumpkin::fr>;
} // namespace bb