// Ceres Solver - A fast non-linear least squares minimizer
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// http://ceres-solver.org/
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// Author: keir@google.com (Keir Mierle)

#include "ceres/scratch_evaluate_preparer.h"

#include <memory>

#include "ceres/parameter_block.h"
#include "ceres/program.h"
#include "ceres/residual_block.h"

namespace ceres::internal {

std::unique_ptr<ScratchEvaluatePreparer[]> ScratchEvaluatePreparer::Create(
    const Program& program, unsigned num_threads) {
  auto preparers = std::make_unique<ScratchEvaluatePreparer[]>(num_threads);
  int max_derivatives_per_residual_block =
      program.MaxDerivativesPerResidualBlock();
  for (unsigned i = 0; i < num_threads; i++) {
    preparers[i].Init(max_derivatives_per_residual_block);
  }
  return preparers;
}

void ScratchEvaluatePreparer::Init(int max_derivatives_per_residual_block) {
  jacobian_scratch_ = std::make_unique<double[]>(
      static_cast<std::size_t>(max_derivatives_per_residual_block));
}

// Point the jacobian blocks into the scratch area of this evaluate preparer.
void ScratchEvaluatePreparer::Prepare(const ResidualBlock* residual_block,
                                      int /* residual_block_index */,
                                      SparseMatrix* /* jacobian */,
                                      double** jacobians) {
  double* jacobian_block_cursor = jacobian_scratch_.get();
  int num_residuals = residual_block->NumResiduals();
  int num_parameter_blocks = residual_block->NumParameterBlocks();
  for (int j = 0; j < num_parameter_blocks; ++j) {
    const ParameterBlock* parameter_block =
        residual_block->parameter_blocks()[j];
    if (parameter_block->IsConstant()) {
      jacobians[j] = nullptr;
    } else {
      jacobians[j] = jacobian_block_cursor;
      jacobian_block_cursor += num_residuals * parameter_block->TangentSize();
    }
  }
}

}  // namespace ceres::internal
