// Info about a specific kernel.
struct Kernel_Info {
  void (*func_ptr)();           // Pointer to kernel function.
  const char *name;             // ASCII version of kernel name.
  cudaFuncAttributes cfa;       // Kernel attributes reported by CUDA.

// Info about GPU and each kernel.
struct GPU_Info {
  double bw_Bps;
  static const int num_kernels_max = 4;
  int num_kernels;
  Kernel_Info ki[num_kernels_max];

__host__ cudaError_t cuda_setup(GPU_Info *gpu_info);

__host__ void time_step_launch(int grid_size, int block_size);

 __host__ void time_step_intersect_launch
(int grid_size, int block_size, int version);

__host__ void time_step_update_pos_launch
(int grid_size, int block_size);

struct Timing_Data {
  clock_t inter_time;
  int inter_count;

struct Helix_Info {
  bool opt_gravity;
  bool opt_test;
  bool opt_end_fixed;
  int opt_use_shared;
  float opt_spring_constant;

  float delta_t;
  float delta_t_mass_inv;
  float delta_t_ma_axis;
  float delta_t_ma_perp_axis;

  int phys_helix_segments;
  float wire_radius;
  float helix_seg_hlength;
  float helix_seg_mass_inv;
  pVect gravity_accel;
  pQuat helix_rn_trans;