/*
   This file contains routines for sorting integers and doubles with a permutation array.

   The word "register"  in this code is used to identify data that is not
   aliased.  For some compilers, this can cause the compiler to fail to
   place inner-loop variables into registers.
 */
#include <petscsys.h> /*I  "petscsys.h"  I*/

#define SWAP(a, b, t) \
  { \
    t = a; \
    a = b; \
    b = t; \
  }

static PetscErrorCode PetscSortIntWithPermutation_Private(const PetscInt v[], PetscInt vdx[], PetscInt right) {
  PetscInt tmp, i, vl, last;

  PetscFunctionBegin;
  if (right <= 1) {
    if (right == 1) {
      if (v[vdx[0]] > v[vdx[1]]) SWAP(vdx[0], vdx[1], tmp);
    }
    PetscFunctionReturn(0);
  }
  SWAP(vdx[0], vdx[right / 2], tmp);
  vl   = v[vdx[0]];
  last = 0;
  for (i = 1; i <= right; i++) {
    if (v[vdx[i]] < vl) {
      last++;
      SWAP(vdx[last], vdx[i], tmp);
    }
  }
  SWAP(vdx[0], vdx[last], tmp);
  PetscCall(PetscSortIntWithPermutation_Private(v, vdx, last - 1));
  PetscCall(PetscSortIntWithPermutation_Private(v, vdx + last + 1, right - (last + 1)));
  PetscFunctionReturn(0);
}

/*@
   PetscSortIntWithPermutation - Computes the permutation of `PetscInt` that gives
   a sorted sequence.

   Not Collective

   Input Parameters:
+  n  - number of values to sort
.  i  - values to sort
-  idx - permutation array.  Must be initialized to 0:n-1 on input.

   Level: intermediate

   Note:
   On output i is unchanged and idx[i] is the position of the i-th smallest index in i.

.seealso: `PetscSortInt()`, `PetscSortRealWithPermutation()`, `PetscSortIntWithArray()`
 @*/
PetscErrorCode PetscSortIntWithPermutation(PetscInt n, const PetscInt i[], PetscInt idx[]) {
  PetscInt j, k, tmp, ik;

  PetscFunctionBegin;
  if (n < 8) {
    for (k = 0; k < n; k++) {
      ik = i[idx[k]];
      for (j = k + 1; j < n; j++) {
        if (ik > i[idx[j]]) {
          SWAP(idx[k], idx[j], tmp);
          ik = i[idx[k]];
        }
      }
    }
  } else {
    PetscCall(PetscSortIntWithPermutation_Private(i, idx, n - 1));
  }
  PetscFunctionReturn(0);
}

/* ---------------------------------------------------------------------- */

static PetscErrorCode PetscSortRealWithPermutation_Private(const PetscReal v[], PetscInt vdx[], PetscInt right) {
  PetscReal vl;
  PetscInt  tmp, i, last;

  PetscFunctionBegin;
  if (right <= 1) {
    if (right == 1) {
      if (v[vdx[0]] > v[vdx[1]]) SWAP(vdx[0], vdx[1], tmp);
    }
    PetscFunctionReturn(0);
  }
  SWAP(vdx[0], vdx[right / 2], tmp);
  vl   = v[vdx[0]];
  last = 0;
  for (i = 1; i <= right; i++) {
    if (v[vdx[i]] < vl) {
      last++;
      SWAP(vdx[last], vdx[i], tmp);
    }
  }
  SWAP(vdx[0], vdx[last], tmp);
  PetscCall(PetscSortRealWithPermutation_Private(v, vdx, last - 1));
  PetscCall(PetscSortRealWithPermutation_Private(v, vdx + last + 1, right - (last + 1)));
  PetscFunctionReturn(0);
}

/*@
   PetscSortRealWithPermutation - Computes the permutation of `PetscReal` that gives
   a sorted sequence.

   Not Collective

   Input Parameters:
+  n  - number of values to sort
.  i  - values to sort
-  idx - permutation array.  Must be initialized to 0:n-1 on input.

   Level: intermediate

   Note:
   i is unchanged on output.

.seealso: `PetscSortReal()`, `PetscSortIntWithPermutation()`
 @*/
PetscErrorCode PetscSortRealWithPermutation(PetscInt n, const PetscReal i[], PetscInt idx[]) {
  PetscInt  j, k, tmp;
  PetscReal ik;

  PetscFunctionBegin;
  if (n < 8) {
    for (k = 0; k < n; k++) {
      ik = i[idx[k]];
      for (j = k + 1; j < n; j++) {
        if (ik > i[idx[j]]) {
          SWAP(idx[k], idx[j], tmp);
          ik = i[idx[k]];
        }
      }
    }
  } else {
    PetscCall(PetscSortRealWithPermutation_Private(i, idx, n - 1));
  }
  PetscFunctionReturn(0);
}

static PetscErrorCode PetscSortStrWithPermutation_Private(const char *v[], PetscInt vdx[], PetscInt right) {
  PetscInt    tmp, i, last;
  PetscBool   gt;
  const char *vl;

  PetscFunctionBegin;
  if (right <= 1) {
    if (right == 1) {
      PetscCall(PetscStrgrt(v[vdx[0]], v[vdx[1]], &gt));
      if (gt) SWAP(vdx[0], vdx[1], tmp);
    }
    PetscFunctionReturn(0);
  }
  SWAP(vdx[0], vdx[right / 2], tmp);
  vl   = v[vdx[0]];
  last = 0;
  for (i = 1; i <= right; i++) {
    PetscCall(PetscStrgrt(vl, v[vdx[i]], &gt));
    if (gt) {
      last++;
      SWAP(vdx[last], vdx[i], tmp);
    }
  }
  SWAP(vdx[0], vdx[last], tmp);
  PetscCall(PetscSortStrWithPermutation_Private(v, vdx, last - 1));
  PetscCall(PetscSortStrWithPermutation_Private(v, vdx + last + 1, right - (last + 1)));
  PetscFunctionReturn(0);
}

/*@C
   PetscSortStrWithPermutation - Computes the permutation of strings that gives
   a sorted sequence.

   Not Collective

   Input Parameters:
+  n  - number of values to sort
.  i  - values to sort
-  idx - permutation array.  Must be initialized to 0:n-1 on input.

   Level: intermediate

   Note:
   i is unchanged on output.

.seealso: `PetscSortInt()`, `PetscSortRealWithPermutation()`
 @*/
PetscErrorCode PetscSortStrWithPermutation(PetscInt n, const char *i[], PetscInt idx[]) {
  PetscInt    j, k, tmp;
  const char *ik;
  PetscBool   gt;

  PetscFunctionBegin;
  if (n < 8) {
    for (k = 0; k < n; k++) {
      ik = i[idx[k]];
      for (j = k + 1; j < n; j++) {
        PetscCall(PetscStrgrt(ik, i[idx[j]], &gt));
        if (gt) {
          SWAP(idx[k], idx[j], tmp);
          ik = i[idx[k]];
        }
      }
    }
  } else {
    PetscCall(PetscSortStrWithPermutation_Private(i, idx, n - 1));
  }
  PetscFunctionReturn(0);
}