#ifndef FESA_SRC_FESA_ELEMENTS_HEX8_LINEAR_TANGENT_CACHE_H_
#define FESA_SRC_FESA_ELEMENTS_HEX8_LINEAR_TANGENT_CACHE_H_

#include <mutex>

#include "fesa/math/matrix.h"

namespace fesa::hex8_internal {
/// @brief Shares one immutable paired Hessian among identical element copies.
/// @note Only call_once preparation writes. Linear readers synchronize through
/// the flag; nonlinear trials do not access this optional state. At most two
/// 24-by-24 matrices (9216 value bytes) are retained after successful preparation.
struct LinearTangentCache {
  std::once_flag preparation;
  bool ready{false};
  Matrix high{0U, 0U};
  Matrix low{0U, 0U};
};
}  // namespace fesa::hex8_internal

#endif  // FESA_SRC_FESA_ELEMENTS_HEX8_LINEAR_TANGENT_CACHE_H_