Date: 2022-08-02T03:14:10+00:00

Actual source code: pheap.c

      2: #include <petsc/private/petscimpl.h>
      3: #include <petscviewer.h>

      5: typedef struct {
      6:   PetscInt id;
      7:   PetscInt value;
      8: } HeapNode;

     10: struct _PetscHeap {
     11:   PetscInt end;                 /* one past the last item */
     12:   PetscInt alloc;               /* length of array */
     13:   PetscInt stash;               /* stash grows down, this points to last item */
     14:   HeapNode *base;
     15: };

     17: /*
     18:  * The arity of the heap can be changed via the parameter B below. Consider the B=2 (arity=4 case below)
     19:  *
     20:  * [00 (sentinel); 01 (min node); 10 (unused); 11 (unused); 0100 (first child); 0101; 0110; 0111; ...]
     21:  *
     22:  * Slots 10 and 11 are referred to as the "hole" below in the implementation.
     23:  */

     25: #define B 1                     /* log2(ARITY) */
     26: #define ARITY (1 << B)          /* tree branching factor */
     27: static inline PetscInt Parent(PetscInt loc)
     28: {
     29:   PetscInt p = loc >> B;
     30:   if (p < ARITY) return (PetscInt)(loc != 1);             /* Parent(1) is 0, otherwise fix entries ending up in the hole */
     31:   return p;
     32: }
     33: #define Value(h,loc) ((h)->base[loc].value)
     34: #define Id(h,loc)  ((h)->base[loc].id)

     36: static inline void Swap(PetscHeap h,PetscInt loc,PetscInt loc2)
     37: {
     38:   PetscInt id,val;
     39:   id                  = Id(h,loc);
     40:   val                 = Value(h,loc);
     41:   h->base[loc].id     = Id(h,loc2);
     42:   h->base[loc].value  = Value(h,loc2);
     43:   h->base[loc2].id    = id;
     44:   h->base[loc2].value = val;
     45: }
     46: static inline PetscInt MinChild(PetscHeap h,PetscInt loc)
     47: {
     48:   PetscInt min,chld,left,right;
     49:   left  = loc << B;
     50:   right = PetscMin(left+ARITY-1,h->end-1);
     51:   chld  = 0;
     52:   min   = PETSC_MAX_INT;
     53:   for (; left <= right; left++) {
     54:     PetscInt val = Value(h,left);
     55:     if (val < min) {
     56:       min  = val;
     57:       chld = left;
     58:     }
     59:   }
     60:   return chld;
     61: }

     63: PetscErrorCode PetscHeapCreate(PetscInt maxsize,PetscHeap *heap)
     64: {
     65:   PetscHeap      h;

     67:   *heap            = NULL;
     68:   PetscMalloc1(1,&h);
     69:   h->end           = 1;
     70:   h->alloc         = maxsize+ARITY; /* We waste all but one slot (loc=1) in the first ARITY slots */
     71:   h->stash         = h->alloc;
     72:   PetscCalloc1(h->alloc,&h->base);
     73:   h->base[0].id    = -1;
     74:   h->base[0].value = PETSC_MIN_INT;
     75:   *heap            = h;
     76:   return 0;
     77: }

     79: PetscErrorCode PetscHeapAdd(PetscHeap h,PetscInt id,PetscInt val)
     80: {
     81:   PetscInt loc,par;

     83:   if (1 < h->end && h->end < ARITY) h->end = ARITY;
     84:   loc = h->end++;
     86:   h->base[loc].id    = id;
     87:   h->base[loc].value = val;

     89:   /* move up until heap condition is satisfied */
     90:   while ((void)(par = Parent(loc)), Value(h,par) > val) {
     91:     Swap(h,loc,par);
     92:     loc = par;
     93:   }
     94:   return 0;
     95: }

     97: PetscErrorCode PetscHeapPop(PetscHeap h,PetscInt *id,PetscInt *val)
     98: {
     99:   PetscInt loc,chld;

    101:   if (h->end == 1) {
    102:     *id  = h->base[0].id;
    103:     *val = h->base[0].value;
    104:     return 0;
    105:   }

    107:   *id  = h->base[1].id;
    108:   *val = h->base[1].value;

    110:   /* rotate last entry into first position */
    111:   loc = --h->end;
    112:   if (h->end == ARITY) h->end = 2; /* Skip over hole */
    113:   h->base[1].id    = Id(h,loc);
    114:   h->base[1].value = Value(h,loc);

    116:   /* move down until min heap condition is satisfied */
    117:   loc = 1;
    118:   while ((chld = MinChild(h,loc)) && Value(h,loc) > Value(h,chld)) {
    119:     Swap(h,loc,chld);
    120:     loc = chld;
    121:   }
    122:   return 0;
    123: }

    125: PetscErrorCode PetscHeapPeek(PetscHeap h,PetscInt *id,PetscInt *val)
    126: {
    127:   if (h->end == 1) {
    128:     *id  = h->base[0].id;
    129:     *val = h->base[0].value;
    130:     return 0;
    131:   }

    133:   *id  = h->base[1].id;
    134:   *val = h->base[1].value;
    135:   return 0;
    136: }

    138: PetscErrorCode PetscHeapStash(PetscHeap h,PetscInt id,PetscInt val)
    139: {
    140:   PetscInt loc;

    142:   loc                = --h->stash;
    143:   h->base[loc].id    = id;
    144:   h->base[loc].value = val;
    145:   return 0;
    146: }

    148: PetscErrorCode PetscHeapUnstash(PetscHeap h)
    149: {
    150:   while (h->stash < h->alloc) {
    151:     PetscInt id = Id(h,h->stash),value = Value(h,h->stash);
    152:     h->stash++;
    153:     PetscHeapAdd(h,id,value);
    154:   }
    155:   return 0;
    156: }

    158: PetscErrorCode PetscHeapDestroy(PetscHeap *heap)
    159: {
    160:   PetscFree((*heap)->base);
    161:   PetscFree(*heap);
    162:   return 0;
    163: }

    165: PetscErrorCode PetscHeapView(PetscHeap h,PetscViewer viewer)
    166: {
    167:   PetscBool      iascii;

    169:   if (!viewer) {
    170:     PetscViewerASCIIGetStdout(PETSC_COMM_SELF,&viewer);
    171:   }
    173:   PetscObjectTypeCompare((PetscObject)viewer,PETSCVIEWERASCII,&iascii);
    174:   if (iascii) {
    175:     PetscViewerASCIIPrintf(viewer,"Heap size %" PetscInt_FMT " with %" PetscInt_FMT " stashed\n",h->end-1,h->alloc-h->stash);
    176:     PetscViewerASCIIPrintf(viewer,"Heap in (id,value) pairs\n");
    177:     PetscIntView(2*(h->end-1),(const PetscInt*)(h->base+1),viewer);
    178:     PetscViewerASCIIPrintf(viewer,"Stash in (id,value) pairs\n");
    179:     PetscIntView(2*(h->alloc-h->stash),(const PetscInt*)(h->base+h->stash),viewer);
    180:   }
    181:   return 0;
    182: }