/*
 * Copyright(C) 1999-2020 National Technology & Engineering Solutions
 * of Sandia, LLC (NTESS).  Under the terms of Contract DE-NA0003525 with
 * NTESS, the U.S. Government retains certain rights in this software.
 *
 * See packages/seacas/LICENSE for details
 */

#include "defs.h"
#include "params.h"
#include "structs.h"
#include <stdlib.h>

/* Figure out how to divide mesh into pieces.  Return true if nonstandard. */
int define_submeshes(int              nsets,        /* number of subsets in this partition */
                     int              cube_or_mesh, /* 0=> hypercube, d=> d-dimensional mesh */
                     int *            mesh_dims,    /* shape of mesh */
                     struct set_info *set,          /* set data for set I'm partitioning */
                     struct set_info *set_info,     /* set data for all sets */
                     int *            subsets,      /* subsets being created by partition */
                     int              inert,        /* using inertial method? */
                     int *            striping,     /* should I partition with parallel cuts? */
                     int *            dir,          /* directions of each cut */
                     int              hop_mtx_special[MAXSETS][MAXSETS] /* hops values if unusual */
)
{
  extern int KL_METRIC; /* 2 => using hops, so generate special values */
  int        ndims;     /* dimension of cut */
  int        dims[3];   /* local copy of mesh_dims to modify */
  int        maxdim;    /* longest dimension of the mesh */
  int        mindim;    /* intest dimension of mesh */
  int        start[3];  /* start in each index of submesh */
  int        width[3];  /* length in each index of submesh */
  int        nbits[3];  /* values for computing hops */
  int        coords[3]; /* location of set in logical grid */
  int        mask[3];   /* values for computing hops */
  int        setnum;    /* number of created set */
  int        flag;      /* return condition */
  int        snaking;   /* is single stripe snaking through grid? */
  int        reverse;   /* should I reverse direction for embedding? */
  int        i, j, k;   /* loop counters */

  dims[0] = set->span[0];
  dims[1] = set->span[1];
  dims[2] = set->span[2];

  ndims = 1;
  while ((2 << ndims) <= nsets) {
    ndims++;
  }

  /* Find the intest and longest directions in mesh. */
  maxdim = -1;
  mindim = dims[0];
  dir[1] = dir[2] = 0;
  for (i = 0; i < cube_or_mesh; i++) {
    if (dims[i] > maxdim) {
      maxdim = dims[i];
      dir[0] = i;
    }
    if (dims[i] < mindim) {
      mindim = dims[i];
    }
  }

  /* Decide whether or not to force striping. */
  i = 0;
  for (j = 0; j < cube_or_mesh; j++) {
    if (set->span[j] > 1) {
      i++;
    }
  }

  *striping = (i <= 1 || nsets == 3 ||
               (maxdim > nsets && (maxdim > .6 * nsets * mindim || (inert && nsets > 2))));

  snaking = !*striping && inert && nsets > 2;

  if (!*striping) {
    if (nsets >= 4) { /* Find direction of second & third cuts. */
      dims[dir[0]] /= 2;
      maxdim = -1;
      for (i = 0; i < cube_or_mesh; i++) {
        if (dims[i] > maxdim) {
          maxdim = dims[i];
          dir[1] = i;
        }
      }
    }

    if (nsets == 8) { /* Find a third direction. */
      dims[dir[1]] /= 2;
      maxdim = -1;
      for (i = 0; i < cube_or_mesh; i++) {
        if (dims[i] > maxdim) {
          maxdim = dims[i];
          dir[2] = i;
        }
      }
    }
    nbits[0] = nbits[1] = nbits[2] = 0;
    for (i = 0; i < ndims; i++) {
      ++nbits[dir[i]];
    }
    for (i = 0; i < 3; i++) {
      mask[i] = (1 << nbits[i]) - 1;
    }
    mask[1] <<= nbits[0];
    mask[2] <<= nbits[0] + nbits[1];
  }

  for (k = nsets - 1; k >= 0; k--) { /* Backwards to not overwrite current set. */

    for (i = 0; i < 3; i++) {
      start[i] = 0;
      width[i] = dims[i] = set->span[i];
    }

    if (*striping) { /* Use longest direction for all cuts. */
      start[dir[0]] = (k * dims[dir[0]] + nsets - 1) / nsets;
      width[dir[0]] = ((k + 1) * dims[dir[0]] + nsets - 1) / nsets - start[dir[0]];
    }

    else { /* Figure out partition based on cut directions. */
      coords[0] = k & mask[0];
      coords[1] = (k & mask[1]) >> nbits[0];
      coords[2] = (k & mask[2]) >> (nbits[0] + nbits[1]);
      if (snaking) {
        reverse = coords[1] & 1;
        if (reverse) {
          coords[0] = mask[0] - coords[0];
        }
        reverse = coords[2] & 1;
        if (reverse) {
          coords[1] = (mask[1] >> nbits[0]) - coords[1];
        }
      }

      for (j = 0; j < ndims; j++) {
        --nbits[dir[j]];
        if (coords[dir[j]] & (1 << nbits[dir[j]])) {
          /* Right side of partition. */
          start[dir[j]] += (width[dir[j]] + 1) / 2;
          width[dir[j]] /= 2;
        }
        else { /* Left side of partition */
          width[dir[j]] = (width[dir[j]] + 1) / 2;
        }
      }

      /* Now restore nbits values. */
      nbits[0] = nbits[1] = nbits[2] = 0;
      for (i = 0; i < ndims; i++) {
        ++nbits[dir[i]];
      }
    }

    for (i = 0; i < 3; i++) {
      start[i] += set->low[i];
    }

    setnum = (start[2] * mesh_dims[1] + start[1]) * mesh_dims[0] + start[0];

    for (i = 0; i < 3; i++) {
      set_info[setnum].low[i]  = start[i];
      set_info[setnum].span[i] = width[i];
    }
    subsets[k] = setnum;
  }

  /* Check to see if hop_mtx is nonstandard. */
  flag = FALSE;
  if (KL_METRIC == 2) {
    if (*striping) {
      flag = TRUE;
      for (i = 0; i < nsets; i++) {
        for (j = 0; j < nsets; j++) {
          hop_mtx_special[i][j] = abs(i - j);
        }
      }
    }

    else if (nsets == 4) {
      if (dir[0] == dir[1] || snaking) {
        flag = TRUE;
        for (i = 0; i < nsets; i++) {
          start[0] = i & mask[0];
          start[1] = (i & mask[1]) >> nbits[0];
          if (snaking) {
            reverse = start[1] & 1;
            if (reverse) {
              start[0] = mask[0] - start[0];
            }
          }
          for (j = i; j < nsets; j++) {
            coords[0] = j & mask[0];
            coords[1] = (j & mask[1]) >> nbits[0];
            if (snaking) {
              reverse = coords[1] & 1;
              if (reverse) {
                coords[0] = mask[0] - coords[0];
              }
            }

            hop_mtx_special[i][j] = hop_mtx_special[j][i] =
                abs(start[0] - coords[0]) + abs(start[1] - coords[1]);
          }
        }
      }
    }
    else if (nsets == 8) {
      if (dir[0] == dir[1] || dir[0] == dir[2] || dir[1] == dir[2] || snaking) {
        flag = TRUE;
        for (i = 0; i < nsets; i++) {
          start[0] = i & mask[0];
          start[1] = (i & mask[1]) >> nbits[0];
          start[2] = (i & mask[2]) >> (nbits[0] + nbits[1]);
          if (snaking) {
            reverse = start[1] & 1;
            if (reverse) {
              start[0] = mask[0] - start[0];
            }
            reverse = start[2] & 1;
            if (reverse) {
              start[1] = (mask[1] >> nbits[0]) - start[1];
            }
          }
          for (j = i; j < nsets; j++) {
            coords[0] = j & mask[0];
            coords[1] = (j & mask[1]) >> nbits[0];
            coords[2] = (j & mask[2]) >> (nbits[0] + nbits[1]);
            if (snaking) {
              reverse = coords[1] & 1;
              if (reverse) {
                coords[0] = mask[0] - coords[0];
              }
              reverse = coords[2] & 1;
              if (reverse) {
                coords[1] = (mask[1] >> nbits[0]) - coords[1];
              }
            }

            hop_mtx_special[i][j] = hop_mtx_special[j][i] =
                abs(start[0] - coords[0]) + abs(start[1] - coords[1]) + abs(start[2] - coords[2]);
          }
        }
      }
    }
  }

  *striping |= snaking;

  return (flag);
}
