#include <math.h>
#include <stdint.h>
#include "kernels.h"
#include "debug.h"

extern uint64_t n_splits;
extern uint64_t block_fail;
extern uint64_t recursive_calls;

int min(int a, int b) {
  return (a > b) ? b : a;
}

uint32_t qmckl_sherman_morrison(
    const uint64_t vLDS, const uint64_t vDim, const uint64_t N_updates,
    const double *__restrict __attribute__((aligned(8))) Updates,
    const uint64_t *__restrict Updates_index, const double breakdown,
    double *__restrict __attribute__((aligned(8))) Slater_inv,
    double *__restrict determinant) {

  const uint32_t Dim = DIM;
  const uint32_t Lds = LDS;

  double __attribute__((aligned(8))) C[DIM];
  double __attribute__((aligned(8))) D[LDS];

  uint32_t l = 0;
  // For each update
  while (l < N_updates) {
    // C = S^{-1} x u_l
    for (uint32_t i = 0; i < Dim; i++) {
      C[i] = 0.0;
      #pragma ivdep
      #pragma vector aligned
      for (uint32_t j = 0; j < Lds; j++) {
        C[i] += Slater_inv[i * Lds + j] * Updates[l * Lds + j]; // regular mat-vec product, but actually working on S_inv^T * U_l.
      }
    }

    // Denominator: v_l^T * C
    const int cui = Updates_index[l] - 1;
    double den = 1.0 + C[cui];

    if (fabs(den) < breakdown) {
      return 1;
    }
    double iden = 1.0 / den;

    // Update det(A)
    if (!determinant)
      *determinant *= den;

    #pragma ivdep
    #pragma vector aligned
    for (uint32_t j = 0; j < Lds; j++) {
      D[j] = Slater_inv[cui * Lds + j]; // selecting proper column of v_l^T * S_inv
    }

    // A^{-1} = A^{-1} - C x D / den
    for (uint32_t i = 0; i < Dim; i++) {
      #pragma ivdep
      #pragma vector aligned
      for (uint32_t j = 0; j < Lds; j++) {
        const double update = C[i] * D[j] * iden;
        Slater_inv[i * Lds + j] -= update;
      }
    }
    l += 1;
  }
  return 0;
}

/*
COMPUTE S^{-1}P - CB^{-1}D  : Dim x LDS,
where S^{-1}P               : Dim x LDS,
      C := S^{-1}PP^TU      : Dim x 2,
      B := 1 + VC           : 2 x 2,
      D := VS^{-1}P         : 2 x LDS,
      P^TU                  : LDS x 2,
      V                     : 2 x Dim
*/
uint32_t qmckl_woodbury_2(const uint64_t vLDS, const uint64_t vDim,
                          const double *__restrict __attribute__((aligned(8)))
                          Updates,
                          const uint64_t *__restrict Updates_index,
                          const double breakdown,
                          double *__restrict __attribute__((aligned(8)))
                          Slater_inv,
                          double *__restrict determinant) {

  const uint32_t Dim = DIM;
  const uint32_t Lds = LDS;

  const uint32_t row1 = (Updates_index[0] - 1);
  const uint32_t row2 = (Updates_index[1] - 1);

  // Compute C = (S^T)^{-1}U : Dim x 2
  double __attribute__((aligned(8))) C[2 * DIM];
  for (uint32_t i = 0; i < Dim; i++) {
    C[i * 2] = 0;
    C[i * 2 + 1] = 0;
    #pragma ivdep
    #pragma vector aligned
    for (uint32_t k = 0; k < Lds; k++) {
      C[i * 2]     += Slater_inv[i * Lds + k] * Updates[k];
      C[i * 2 + 1] += Slater_inv[i * Lds + k] * Updates[Lds + k];
    }
  }

  // Compute B = 1 + VC : 2 x 2
  const double B0 = C[row1 * 2] + 1;
  const double B1 = C[row1 * 2 + 1];
  const double B2 = C[row2 * 2];
  const double B3 = C[row2 * 2 + 1] + 1;

  // Check if determinant of inverted matrix is not zero
  double det = B0 * B3 - B1 * B2;
  if (fabs(det) < breakdown) {
    return 1;
  }

  // Update det(S) when passed
  if (determinant != NULL)
    *determinant *= det;

  // Compute B^{-1} with explicit formula for 2 x 2 inversion
  double __attribute__((aligned(8))) Binv[4], idet = 1.0 / det;
  Binv[0] = idet * B3;
  Binv[1] = -1.0 * idet * B1;
  Binv[2] = -1.0 * idet * B2;
  Binv[3] = idet * B0;

  // tmp = B^{-1}D : 2 x LDS
  double __attribute__((aligned(8))) tmp[2 * LDS];
  double *__restrict r1dim = &(Slater_inv[row1 * Lds]);
  double *__restrict r2dim = &(Slater_inv[row2 * Lds]);
  #pragma ivdep
  #pragma vector aligned
  for (uint32_t j = 0; j < Lds; j++) {
    tmp[j]       = Binv[0] * r1dim[j] + Binv[1] * r2dim[j];
    tmp[Lds + j] = Binv[2] * r1dim[j] + Binv[3] * r2dim[j];
  }

  // Compute (S^T)^{-1} - C * tmp : Dim x Lds
  for (uint32_t i = 0; i < Dim; i++) {
    #pragma ivdep
    #pragma vector aligned
    for (uint32_t j = 0; j < Lds; j++) {
      Slater_inv[i * Lds + j] -= C[i * 2]     * tmp[j];
      Slater_inv[i * Lds + j] -= C[i * 2 + 1] * tmp[Lds + j];
    }
  }

  return 0;
}

/*
COMPUTE (S^T)^{-1} - CB^{-1}D : Dim x LDS,
where S^T                     : Dim x LDS,
      C := (S^T)^{-1}U        : Dim x 3,
      B := 1 + VC             : 3 x 3,
      D := V(S^T)^{-1}        : 3 x LDS,
      U                       : LDS x 3,
      V                       : 3 x Dim
*/
uint32_t  qmckl_woodbury_3(const uint64_t vLDS, const uint64_t vDim,
                          const double *__restrict __attribute__((aligned(8)))
                          Updates,
                          const uint64_t *__restrict Updates_index,
                          const double breakdown,
                          double *__restrict __attribute__((aligned(8)))
                          Slater_inv,
                          double *__restrict determinant) {

  const uint32_t Dim = DIM;
  const uint32_t Lds = LDS;

  const uint32_t row1 = (Updates_index[0] - 1);
  const uint32_t row2 = (Updates_index[1] - 1);
  const uint32_t row3 = (Updates_index[2] - 1);

  // Compute C = (S^T)^{-1}U : Dim x 3
  double __attribute__((aligned(8))) C[3 * DIM];
  for (uint32_t i = 0; i < Dim; i++) {
    C[i * 3] = 0;
    C[i * 3 + 1] = 0;
    C[i * 3 + 2] = 0;
    #pragma ivdep
    #pragma vector aligned
    for (uint32_t k = 0; k < Lds; k++) {
      C[i * 3] += Slater_inv[i * Lds + k] * Updates[k];
      C[i * 3 + 1] += Slater_inv[i * Lds + k] * Updates[Lds + k];
      C[i * 3 + 2] += Slater_inv[i * Lds + k] * Updates[2 * Lds + k];
    }
  }

  // Compute B = 1 + VC : 3 x 3
  const double B0 = C[row1 * 3] + 1;
  const double B1 = C[row1 * 3 + 1];
  const double B2 = C[row1 * 3 + 2];
  const double B3 = C[row2 * 3];
  const double B4 = C[row2 * 3 + 1] + 1;
  const double B5 = C[row2 * 3 + 2];
  const double B6 = C[row3 * 3];
  const double B7 = C[row3 * 3 + 1];
  const double B8 = C[row3 * 3 + 2] + 1;

  // Check if determinant of B is not too close to zero
  double det;
  det = B0 * (B4 * B8 - B5 * B7) - B1 * (B3 * B8 - B5 * B6) +
        B2 * (B3 * B7 - B4 * B6);
  if (fabs(det) < breakdown) {
    return 1;
  }

  // Update det(Slater) if passed
  if (determinant != NULL)
    *determinant *= det;

  // Compute B^{-1} with explicit formula for 3 x 3 inversion
  double __attribute__((aligned(8))) Binv[9], idet = 1.0 / det;
  Binv[0] =  (B4 * B8 - B7 * B5) * idet;
  Binv[1] = -(B1 * B8 - B7 * B2) * idet;
  Binv[2] =  (B1 * B5 - B4 * B2) * idet;
  Binv[3] = -(B3 * B8 - B6 * B5) * idet;
  Binv[4] =  (B0 * B8 - B6 * B2) * idet;
  Binv[5] = -(B0 * B5 - B3 * B2) * idet;
  Binv[6] =  (B3 * B7 - B6 * B4) * idet;
  Binv[7] = -(B0 * B7 - B6 * B1) * idet;
  Binv[8] =  (B0 * B4 - B3 * B1) * idet;

  // tmp = B^{-1}D : 3 x LDS
  double __attribute__((aligned(8))) tmp[3 * LDS];
  double *__restrict r1dim = &(Slater_inv[row1 * LDS]);
  double *__restrict r2dim = &(Slater_inv[row2 * LDS]);
  double *__restrict r3dim = &(Slater_inv[row3 * LDS]);
  #pragma ivdep
  #pragma vector aligned
  for (uint32_t j = 0; j < Lds; j++) {
    tmp[j]           = Binv[0] * r1dim[j] + Binv[1] * r2dim[j] + Binv[2] * r3dim[j];
    tmp[Lds + j]     = Binv[3] * r1dim[j] + Binv[4] * r2dim[j] + Binv[5] * r3dim[j];
    tmp[2 * Lds + j] = Binv[6] * r1dim[j] + Binv[7] * r2dim[j] + Binv[8] * r3dim[j];
  }

  // Compute (S^T)^{-1} - C * tmp : Dim x Lds
  for (uint32_t i = 0; i < Dim; i++) {
    #pragma ivdep
    #pragma vector aligned
    for (uint32_t j = 0; j < Lds; j++) {
      Slater_inv[i * Lds + j] -= C[i * 3]     * tmp[j];
      Slater_inv[i * Lds + j] -= C[i * 3 + 1] * tmp[Lds + j];
      Slater_inv[i * Lds + j] -= C[i * 3 + 2] * tmp[2 * Lds + j];
    }
  }

  return 0;
}

/*
COMPUTE S^{-1} - C B^{-1} D : Dim x LDS,
where S^{-1}                : Dim x LDS,
      C := S^{-1} U         : Dim x K, dgemm
      B := 1 + V C          : K x K, copy
      D := V S^{-1}         : K x LDS, copy
      U                     : LDS x K,
      V                     : K x Dim
      tmp := B^{-1} D       : K x LDS, dgemm
      S = S - C tmp         : Dim x LDS, dgemm
*/
uint32_t qmckl_woodbury_k(const uint64_t vLDS,
                          const uint64_t vDim,
                          const uint64_t N_updates,
                          const double *__restrict __attribute__((aligned(8))) Updates,
                          const uint64_t *__restrict Updates_index,
                          const double breakdown,
                          double *__restrict __attribute__((aligned(8))) Slater_inv,
                          double *__restrict determinant) {

  const uint32_t Dim = DIM;
  const uint32_t Lds = LDS;

  // Compute C = S^{-1} U : Dim x K : standard dgemm
  double *C = calloc(1, DIM * N_updates * sizeof(double));
  double alpha = 1.0, beta = 0.0;

  cblas_dgemm(CblasRowMajor, CblasNoTrans, CblasTrans,
              Dim, N_updates, Lds,
              alpha, Slater_inv, Lds, Updates, Lds,
              beta, C, N_updates);

  // Construct B = 1 + V C : K x K : selecting and copying row from C into B. Can maybe be off-loaded to GPU by splitting in N_updates tiles of N_updates strides, using PARALLEL and SIMD
  // Construct D = V S^{-1} : K x LDS
  double B[N_updates * N_updates], D[N_updates * LDS];
  for (uint32_t i = 0; i < N_updates; i++) {
    const uint32_t row = Updates_index[i] - 1;
    for (uint32_t j = 0; j < N_updates  ; j++) B[i * N_updates + j] = C[row * N_updates + j] + (i == j);
    for (uint32_t j = 0; j < Lds; j++) D[i * Lds + j] = Slater_inv[row * Lds + j];
  }

  // Compute determinant by LU decomposition
  int ipiv[N_updates];
  (void) LAPACKE_dgetrf(LAPACK_ROW_MAJOR, N_updates, N_updates, B, N_updates, ipiv);

  double det = 1.0;
  int j = 0;
  for (uint32_t i = 0; i < N_updates; i++) {
    j += min(ipiv[i] - i, 1);
    det *= B[(N_updates + 1) * i];
  }
  if ((j & 1) == 0) det = -det; // multiply det with -1 if j is even

  // Check if determinant of B is not too close to zero
  if (fabs(det) < breakdown) {
    return 1;
  }

  // Update det(Slater) if passed
  if (determinant) *determinant *= det;

  // Compute B^{-1} with explicit formula for K x K inversion
  (void) LAPACKE_dgetri(LAPACK_ROW_MAJOR, N_updates, B, N_updates, ipiv);

  // tmp1 = B^{-1} D : KxLDS = KxK X KxLDS : standard dgemm
  double tmp1[N_updates * LDS];
  cblas_dgemm(CblasRowMajor, CblasNoTrans, CblasNoTrans,
              N_updates, LDS, N_updates,
              alpha, B, N_updates, D, LDS,
              beta, tmp1, LDS);

  // Compute S^{-1} - C * tmp1 : Dim x LDS : standard dgemm
  alpha = -1.0, beta = 1.0;
  cblas_dgemm(CblasRowMajor, CblasNoTrans, CblasNoTrans,
              Dim, LDS, N_updates,
              alpha, C, N_updates, tmp1, LDS,
              beta, Slater_inv, LDS);

  return 0;
}

#ifdef HAVE_CUBLAS_OFFLOAD
uint32_t qmckl_woodbury_k_cublas_offload(cublasHandle_t handle,
                                         const uint64_t vLDS,
                                         const uint64_t vDim,
                                         const uint64_t N_updates,
                                         const double* Updates,
                                         const uint64_t* Updates_index,
                                         const double breakdown,
                                         double* Slater_inv,
                                         double* determinant)
{
  const uint32_t Dim = DIM;
  const uint32_t Lds = LDS;

  double alpha, beta;
  int* ipiv = calloc(1, sizeof *ipiv * N_updates);
  double* C  = calloc(1, sizeof *C * Dim * N_updates);
  double* B  = calloc(1, sizeof *B * N_updates * N_updates);
  double* D  = calloc(1, sizeof *D * N_updates * Lds);
  double* T1 = calloc(1, sizeof *T1 * N_updates * Lds);
  double* T2 = calloc(1, sizeof *T2 * Dim * Lds);

  #pragma omp target enter data map(to:    Updates[0:Lds*N_updates], \
                                           Updates_index[0:N_updates], \
                                           Slater_inv[0:Dim*Lds]) \
                                map(alloc: B[0:N_updates*N_updates], \
                                           C[0:Dim*N_updates], \
                                           D[0:N_updates*Lds], \
                                           T1[0:N_updates*Lds], \
                                           T2[0:Dim*Lds], \
                                           ipiv[0:N_updates])

  #pragma omp target data use_device_ptr(Slater_inv, Updates, C) // compute C ON DEVICE
  {
    alpha = 1.0f, beta = 0.0f;
    (void) cublasDgemm(handle,
                      CUBLAS_OP_T, CUBLAS_OP_N,
                      N_updates, Dim, Lds,
                      &alpha, Updates, Lds, Slater_inv, Lds,
                      &beta, C, N_updates);
  }

  // Construct B = 1 + V C : K x K
  // Construct D = V S^{-1} : K x LDS
  #pragma omp target teams distribute parallel for // compute B, D ON DEVICE
  for (uint32_t i = 0; i < N_updates; i++)
  {
    const uint32_t row = Updates_index[i] - 1;
    for (uint32_t j = 0; j < N_updates  ; j++)
    {
      B[i * N_updates + j] = C[row * N_updates + j] + (i == j);
    }
    for (uint32_t j = 0; j < Lds; j++)
    {
      D[i * Lds + j] = Slater_inv[row * Lds + j];
    }
  }
  #pragma omp target update from(B[0:N_updates*N_updates]) // Update B ON HOST

  // Compute determinant by LU decomposition
  (void) LAPACKE_dgetrf(LAPACK_ROW_MAJOR, N_updates, N_updates, B, N_updates, ipiv);
  #pragma omp target update to(B[0:N_updates*N_updates], ipiv[0:N_updates]) // Update B ON DEVICE

  double det = 1.0f; uint32_t j = 0;
  #pragma omp target teams distribute parallel for // compute det ON DEVICE
  for (uint32_t i = 0; i < N_updates; i++)
  {
    j += min(ipiv[i] - i, 1);
    det *= B[(N_updates + 1) * i]; // update determinant
  }
  if ((j & 1) == 0) det = -det; // multiply det with -1 if j is even

  // Check if determinant of B is not too close to zero
  if (fabs(det) < breakdown) return det;

  // Update det(Slater) if passed
  if (determinant) *determinant *= det;

  // Compute B^{-1}
  (void) LAPACKE_dgetri(LAPACK_ROW_MAJOR, N_updates, B, N_updates, ipiv); // compute B^-1 ON HOST
  #pragma omp target update to(B[:N_updates*N_updates]) // Update B^-1 TO DEVICE

  // T1 = B^{-1} D : KxLDS = KxK X KxLDS : standard dgemm
  #pragma omp target data use_device_ptr(D, B, T1) // compute T1 ON DEVICE
  {
    alpha = 1.0, beta = 0.0;
    (void) cublasDgemm(handle,
                      CUBLAS_OP_N, CUBLAS_OP_N,
                      Lds, N_updates, N_updates,
                      &alpha, D, Lds, B, N_updates,
                      &beta, T1, Lds);
  }

  // Compute T2 <- C * T1 : Dim x LDS : standard dgemm
  #pragma omp target data use_device_ptr(T1, C, T2) // compute T2 ONM DEVICE
  {
    alpha = 1.0f, beta = 0.0f;
    (void) cublasDgemm(handle,
                      CUBLAS_OP_N, CUBLAS_OP_N,
                      Dim, Lds, N_updates,
                      &alpha, T1, Lds, C, N_updates,
                      &beta, T2, Lds);
  }

  // Compute S^{-1} <- S^{-1} - T2 : Dim x LDS : standard dgemm
  #pragma omp target teams distribute parallel for // compute S^-1 ON DEVICE
  for (uint32_t i = 0; i < Dim * Lds; i++)
  {
    Slater_inv[i] = Slater_inv[i] - T2[i];
  }
  #pragma omp target update from(Slater_inv[0:Dim*Lds]) // update S^-1 ON HOST

  #pragma omp target exit data map(delete: Updates[0:Lds*N_updates], \
                                           Updates_index[0:N_updates], \
                                           Slater_inv[0:Dim*Lds], \
                                           B[0:N_updates*N_updates], \
                                           C[0:Dim*N_updates], \
                                           D[0:N_updates*Lds], \
                                           T1[0:N_updates*Lds], \
                                           T2[0:Dim*Lds], \
                                           ipiv[0:N_updates])

//  free(ipiv);
  free(B);
  free(C);
  free(D);
  free(T1);
  free(T2);

  return 0;
}
#endif

uint32_t qmckl_slagel_splitting(
    const uint64_t vLDS, const uint64_t vDim, uint64_t N_updates,
    const double *__restrict __attribute__((aligned(8))) Updates,
    const uint64_t *__restrict Updates_index, const double breakdown,
    double *__restrict __attribute__((aligned(8))) Slater_inv,
    double *__restrict __attribute__((aligned(8))) later_updates,
    uint64_t *__restrict later_index, uint64_t *__restrict later,
    double *__restrict determinant) {

  const uint32_t Dim = DIM;
  const uint32_t Lds = LDS;

  double __attribute__((aligned(8))) C[LDS];
  double __attribute__((aligned(8))) D[LDS];

  uint32_t l = 0;
  // For each update
  while (l < N_updates) {
    // C = S^{-1} x U_l
    for (uint32_t i = 0; i < Dim; i++) {
      C[i] = 0.0;
      #pragma ivdep
      #pragma vector aligned
      for (uint32_t j = 0; j < Lds; j++) {
        C[i] += Slater_inv[i * Lds + j] * Updates[l * Lds + j]; // regular mat-vec product, but actually working on S_inv^T * U_l.
      }
    }

    // Denominator
    const int cui = Updates_index[l] - 1;
    double den = 1.0 + C[cui];
    // printf("test breakdown = %f, den = %f, C[cui] = %f, cui = %d\n", breakdown, fabs(den), C[cui], cui);
    if (fabs(den) < breakdown) { // Here is decided to split the update, or not.
      // printf("Split! breakdown = %f\n", breakdown);
      n_splits += 1;

      // U_l = U_l / 2: split the update in 2 equal halves and save the second halve
      // in later_updates
      #pragma ivdep
      #pragma vector aligned
      for (uint32_t i = 0; i < Lds; i++) {
        later_updates[*later * Lds + i] = Updates[l * Lds + i] / 2.0;
        C[i] /= 2.0;
      }
      later_index[*later] = Updates_index[l];
      (*later)++;

      den = 1.0 + C[cui];
    } // From here onwards we continue with applying the first halve of the update to Slater_inv
    double iden = 1.0 / den;

    if (!determinant) *determinant *= den;

    // D = v^T x S^{-1} : 1 x LDS
    #pragma ivdep
    #pragma vector aligned
    for (uint32_t j = 0; j < Lds; j++) {
      D[j] = Slater_inv[cui * Lds + j];
    }

    // S^{-1} = S^{-1} - C x D / den
    for (uint32_t i = 0; i < Dim; i++) {
      #pragma ivdep
      #pragma vector aligned
      for (uint32_t j = 0; j < Lds; j++) {
        const double update = C[i] * D[j] * iden;
        Slater_inv[i * Lds + j] -= update;
      }
    }
    l += 1;
  }

  return 0;
}

uint32_t qmckl_sherman_morrison_splitting(
    const uint64_t vLDS, const uint64_t vDim, const uint64_t N_updates,
    const double *__restrict __attribute__((aligned(8))) Updates,
    const uint64_t *__restrict Updates_index, const double breakdown,
    double *__restrict __attribute__((aligned(8))) Slater_inv,
    double *__restrict determinant) {

  const uint32_t Dim = DIM;
  const uint32_t Lds = LDS;

  double __attribute__((aligned(8))) later_updates[LDS * N_updates];
  uint64_t later_index[N_updates];
  uint64_t later = 0;
  // uint32_t rc;

  (void) qmckl_slagel_splitting(Lds, Dim, N_updates, Updates, Updates_index,
                              breakdown, Slater_inv, later_updates, later_index,
                              &later, determinant);
  // rc = qmckl_slagel_splitting(Lds, Dim, N_updates, Updates, Updates_index,
  //                             breakdown, Slater_inv, later_updates, later_index,
  //                             &later, determinant);
  // if (rc != 0) printf("Something when catastrophically wrong in QMCKL_SLAGEL_SPLITTING\n");

  if (later > 0) {
    recursive_calls++;
    // printf("Later > 0\n");
    (void) qmckl_sherman_morrison_splitting(Lds, Dim, later, later_updates,
                                          later_index, breakdown, Slater_inv,
                                          determinant);

    // rc = qmckl_sherman_morrison_splitting(Lds, Dim, later, later_updates,
    //                                       later_index, breakdown, Slater_inv,
    //                                       determinant);
    // if (rc != 0) printf("Something when catastrophically wrong in QMCKL_SHERMAN_MORRISON_SPLITTING\n");
  }

  return 0;
}

uint32_t qmckl_sherman_morrison_smw32s(
    const uint64_t vLDS, const uint64_t vDim, const uint64_t N_updates,
    const double *__restrict __attribute__((aligned(8))) Updates,
    const uint64_t *__restrict Updates_index, const double breakdown,
    double *__restrict __attribute__((aligned(8))) Slater_inv,
    double *__restrict determinant) {

  const uint32_t Dim = DIM;
  const uint32_t Lds = LDS;

  double __attribute__((aligned(8))) later_updates[LDS * N_updates];
  uint64_t later_index[N_updates];
  uint64_t later = 0;
  uint32_t rc;

  if (N_updates == 4) { // Special case for 4 rank-1 updates: 2+2
    rc = qmckl_woodbury_2(Lds, Dim, Updates, Updates_index,
                  breakdown, Slater_inv, determinant);
    if (rc != 0) { // Send the entire block to slagel_splitting
      block_fail += 1;
      uint64_t l = 0;
      rc = qmckl_slagel_splitting(Lds, Dim, 2, Updates,
                    Updates_index, breakdown, Slater_inv,
                    later_updates + (Lds * later),
                    later_index + later, &l, determinant);
      later += l;
    }
    rc = qmckl_woodbury_2(Lds, Dim, &Updates[2*Lds], &Updates_index[2],
                  breakdown, Slater_inv, determinant);
    if (rc != 0) { // Send the entire block to slagel_splitting
      block_fail += 1;
      uint64_t l = 0;
      rc = qmckl_slagel_splitting(Lds, Dim, 2, &Updates[2*Lds],
                    &Updates_index[2], breakdown, Slater_inv,
                    later_updates + (Lds * later),
                    later_index + later, &l, determinant);
      later += l;
    }
    if (later > 0) {
      recursive_calls++;
      rc = qmckl_sherman_morrison_splitting(Lds, Dim, later, later_updates,
                                            later_index, breakdown, Slater_inv,
                                            determinant);
    }
    return 0;
  }

  // And for the other cases != 4, 6
  // Apply first 3*n_of_3blocks updates in n_of_3blocks blocks of 3 updates with
  // Woodbury 3x3 kernel
  uint32_t n_of_3blocks = N_updates / 3;
  uint32_t remainder = N_updates % 3;
  uint32_t length_3block = 3 * Lds;

  if (n_of_3blocks > 0) {
    for (uint32_t i = 0; i < n_of_3blocks; i++) {
      const double *Updates_3block = &Updates[i * length_3block];
      const uint64_t *Updates_index_3block = &Updates_index[i * 3];
      rc = qmckl_woodbury_3(Lds, Dim, Updates_3block, Updates_index_3block,
                            breakdown, Slater_inv, determinant);
      if (rc != 0) { // Send the entire block to slagel_splitting
        // printf("QMCKL_WOODBURY_3 failed. Sending to QMCKL_SLAGEL_SPLITTING\n");
        block_fail += 1;
        uint64_t l = 0;
        rc = qmckl_slagel_splitting(Lds, Dim, 3, Updates_3block,
                                    Updates_index_3block, breakdown, Slater_inv,
                                    later_updates + (Lds * later),
                                    later_index + later, &l, determinant);
        // if (rc != 0) printf("Something when catastrophically wrong in QMCKL_SLAGEL_SPLITTING\n");
        later += l;
      }
    }
  }

  // Apply last remaining block of 2 updates with Woodbury 2x2 kernel
  if (remainder == 2) {
    const double *Updates_2block = &Updates[n_of_3blocks * length_3block];
    const uint64_t *Updates_index_2block = &Updates_index[3 * n_of_3blocks];
    rc = qmckl_woodbury_2(Lds, Dim, Updates_2block, Updates_index_2block,
                          breakdown, Slater_inv, determinant);
    if (rc != 0) { // Send the entire block to slagel_splitting
      // printf("QMCKL_WOODBURY_2 failed. Sending to QMCKL_SLAGEL_SPLITTING\n");
      block_fail += 1;
      uint64_t l = 0;
      rc = qmckl_slagel_splitting(Lds, Dim, 2, Updates_2block,
                                  Updates_index_2block, breakdown, Slater_inv,
                                  later_updates + (Lds * later),
                                  later_index + later, &l, determinant);
      // if (rc != 0) printf("Something when catastrophically wrong in QMCKL_SLAGEL_SPLITTING\n");
      later += l;
    }
  }

  // Apply last remaining update with slagel_splitting
  if (remainder == 1) {
    // // printf("Sending single update to QMCKL_SLAGEL_SPLITTING\n");
    const double *Updates_1block = &Updates[n_of_3blocks * length_3block];
    const uint64_t *Updates_index_1block = &Updates_index[3 * n_of_3blocks];
    uint64_t l = 0;
    rc = qmckl_slagel_splitting(Lds, Dim, 1, Updates_1block,
                                Updates_index_1block, breakdown, Slater_inv,
                                later_updates + (Lds * later),
                                later_index + later, &l, determinant);
    // if (rc != 0) printf("Something when catastrophically wrong in QMCKL_SLAGEL_SPLITTING\n");
    later += l;
  }

  if (later > 0) {
    recursive_calls++;
    // printf("Sending remaining updates to QMCKL_SHERMAN_MORRISON_SPLITTING\n");
    rc = qmckl_sherman_morrison_splitting(Lds, Dim, later, later_updates,
                                          later_index, breakdown, Slater_inv,
                                          determinant);
    // if (rc != 0) printf("Something when catastrophically wrong in QMCKL_SHERMAN_MORRISON_SPLITTING\n");
  }
  return 0;
}

// Sherman Morrison, leaving zero denominators for later
uint32_t qmckl_sherman_morrison_later(
    const uint64_t vLDS, const uint64_t vDim, const uint64_t N_updates,
    const double *__restrict __attribute__((aligned(8))) Updates,
    const uint64_t *__restrict Updates_index, const double breakdown,
    double *__restrict __attribute__((aligned(8))) Slater_inv,
    double *__restrict determinant) {

  const uint32_t Dim = DIM;
  const uint32_t Lds = LDS;

  double __attribute__((aligned(8))) C[DIM];
  double __attribute__((aligned(8))) D[LDS];

  double __attribute__((aligned(8))) later_updates[LDS * N_updates];
  uint64_t later_index[N_updates];
  uint64_t later = 0;

  uint32_t l = 0;
  // For each update
  while (l < N_updates) {

    // C = A^{-1} x U_l
    for (uint32_t i = 0; i < Dim; i++) {
      C[i] = 0.0;
      #pragma ivdep
      #pragma vector aligned
      for (uint32_t j = 0; j < Lds; j++) {
        C[i] += Slater_inv[i * Lds + j] * Updates[l * Lds + j]; // regular mat-vec product, but actually working on S_inv^T * U_l.
      }
    }

    // Denominator
    const int cui = Updates_index[l] - 1;
    double den = 1.0 + C[cui];
    if (fabs(den) < breakdown) {
      #pragma ivdep
      #pragma vector aligned
      // for (uint32_t i = 0; i < Dim; i++) {
      for (uint32_t i = 0; i < Lds; i++) {
        later_updates[later * Lds + i] = Updates[l * Lds + i];
      }
      later_index[later] = Updates_index[l];
      later++;
      l += 1;
      continue;
    }
    double iden = 1.0 / den;

    if (!determinant) *determinant *= den;

    // D = v^T x A^{-1}
    #pragma ivdep
    #pragma vector aligned
    for (uint32_t j = 0; j < Lds; j++) {
      D[j] = Slater_inv[cui * Lds + j];
    }

    // S^{-1} = S^{-1} - C x D / den
    for (uint32_t i = 0; i < Dim; i++) {
      #pragma ivdep
      #pragma vector aligned
      for (uint32_t j = 0; j < Lds; j++) {
        const double update = C[i] * D[j] * iden;
        Slater_inv[i * Lds + j] -= update;
      }
    }
    l += 1;
  }

  if (later == N_updates) { // If all the updates have failed, exit early with an error
    return 1;
  }
  else if (later > 0) { // If some have failed, make a recursive call
    recursive_calls++;
    (void) qmckl_sherman_morrison_later(Lds, Dim, later, later_updates,
                      later_index, breakdown, Slater_inv, determinant);
  }

  return 0;

}

// Inplace inverse n x n matrix A.
// returns:
//   ret = 0 on success
//   ret < 0 illegal argument value
//   ret > 0 singular matrix
lapack_int inverse(double *a, uint64_t m, uint64_t n) {
  int ipiv[m + 1];
  lapack_int ret;
  ret = LAPACKE_dgetrf(LAPACK_ROW_MAJOR, m, n, a, n, ipiv);
  if (ret != 0) return ret;
  ret = LAPACKE_dgetri(LAPACK_ROW_MAJOR, n, a, n, ipiv);
  return ret;
}