/*====================================================================*
- Copyright (C) 2001 Leptonica. All rights reserved.
- This software is distributed in the hope that it will be
- useful, but with NO WARRANTY OF ANY KIND.
- No author or distributor accepts responsibility to anyone for the
- consequences of using this software, or for whether it serves any
- particular purpose or works at all, unless he or she says so in
- writing. Everyone is granted permission to copy, modify and
- redistribute this source code, for commercial or non-commercial
- purposes, with the following restrictions: (1) the origin of this
- source code must not be misrepresented; (2) modified versions must
- be plainly marked as such; and (3) this notice may not be removed
- or altered from any source or modified source distribution.
*====================================================================*/
/*
* heap.c
*
* Create/Destroy L_Heap
* L_HEAP *lheapCreate()
* void *lheapDestroy()
*
* Operations to add/remove to/from the heap
* l_int32 lheapAdd()
* l_int32 lheapExtendArray()
* void *lheapRemove()
*
* Heap operations
* l_int32 lheapSwapUp()
* l_int32 lheapSwapDown()
* l_int32 lheapSort()
* l_int32 lheapSortStrictOrder()
*
* Accessors
* l_int32 lheapGetCount()
*
* Debug output
* l_int32 lheapPrint()
*
* The L_Heap is useful to implement a priority queue, that is sorted
* on a key in each element of the heap. The heap is an array
* of nearly arbitrary structs, with a l_float32 the first field.
* This field is the key on which the heap is sorted.
*
* Internally, we keep track of the heap size, n. The item at the
* root of the heap is at the head of the array. Items are removed
* from the head of the array and added to the end of the array.
* When an item is removed from the head, the item at the end
* of the array is moved to the head. When items are either
* added or removed, it is usually necesary to swap array items
* to restore the heap order. It is guaranteed that the number
* of swaps does not exceed log(n).
*
* -------------------------- N.B. ------------------------------
* The items on the heap (or, equivalently, in the array) are cast
* to void*. Their key is a l_float32, and it is REQUIRED that the
* key be the first field in the struct. That allows us to get the
* key by simply dereferencing the struct. Alternatively, we could
* choose (but don't) to pass an application-specific comparison
* function into the heap operation functions.
* -------------------------- N.B. ------------------------------
*/
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include "allheaders.h"
static const l_int32 MIN_BUFFER_SIZE = 20; /* n'importe quoi */
static const l_int32 INITIAL_BUFFER_ARRAYSIZE = 128; /* n'importe quoi */
#define SWAP_ITEMS(i, j) { void *tempitem = lh->array[(i)]; \
lh->array[(i)] = lh->array[(j)]; \
lh->array[(j)] = tempitem; }
/*--------------------------------------------------------------------------*
* L_Heap create/destroy *
*--------------------------------------------------------------------------*/
/*!
* lheapCreate()
*
* Input: size of ptr array to be alloc'd (0 for default)
* direction (L_SORT_INCREASING, L_SORT_DECREASING)
* Return: lheap, or null on error
*/
L_HEAP *
lheapCreate(l_int32 nalloc,
l_int32 direction)
{
L_HEAP *lh;
PROCNAME("lheapCreate");
if (nalloc < MIN_BUFFER_SIZE)
nalloc = MIN_BUFFER_SIZE;
/* Allocate ptr array and initialize counters. */
if ((lh = (L_HEAP *)CALLOC(1, sizeof(L_HEAP))) == NULL)
return (L_HEAP *)ERROR_PTR("lh not made", procName, NULL);
if ((lh->array = (void **)CALLOC(nalloc, sizeof(void *))) == NULL)
return (L_HEAP *)ERROR_PTR("ptr array not made", procName, NULL);
lh->nalloc = nalloc;
lh->n = 0;
lh->direction = direction;
return lh;
}
/*!
* lheapDestroy()
*
* Input: &lheap (<to be nulled>)
* freeflag (TRUE to free each remaining struct in the array)
* Return: void
*
* Notes:
* (1) Use freeflag == TRUE when the items in the array can be
* simply destroyed using free. If those items require their
* own destroy function, they must be destroyed before
* calling this function, and then this function is called
* with freeflag == FALSE.
* (2) To destroy the lheap, we destroy the ptr array, then
* the lheap, and then null the contents of the input ptr.
*/
void
lheapDestroy(L_HEAP **plh,
l_int32 freeflag)
{
l_int32 i;
L_HEAP *lh;
PROCNAME("lheapDestroy");
if (plh == NULL) {
L_WARNING("ptr address is NULL", procName);
return;
}
if ((lh = *plh) == NULL)
return;
if (freeflag) { /* free each struct in the array */
for (i = 0; i < lh->n; i++)
FREE(lh->array[i]);
}
else if (lh->n > 0) /* freeflag == FALSE but elements exist on array */
L_WARNING_INT("memory leak of %d items in lheap!", procName, lh->n);
if (lh->array)
FREE(lh->array);
FREE(lh);
*plh = NULL;
return;
}
/*--------------------------------------------------------------------------*
* Accessors *
*--------------------------------------------------------------------------*/
/*!
* lheapAdd()
*
* Input: lheap
* item to be added to the tail of the heap
* Return: 0 if OK, 1 on error
*/
l_int32
lheapAdd(L_HEAP *lh,
void *item)
{
PROCNAME("lheapAdd");
if (!lh)
return ERROR_INT("lh not defined", procName, 1);
if (!item)
return ERROR_INT("item not defined", procName, 1);
/* If necessary, expand the allocated array by a factor of 2 */
if (lh->n >= lh->nalloc)
lheapExtendArray(lh);
/* Add the item */
lh->array[lh->n] = item;
lh->n++;
/* Restore the heap */
lheapSwapUp(lh, lh->n - 1);
return 0;
}
/*!
* lheapExtendArray()
*
* Input: lheap
* Return: 0 if OK, 1 on error
*/
l_int32
lheapExtendArray(L_HEAP *lh)
{
PROCNAME("lheapExtendArray");
if (!lh)
return ERROR_INT("lh not defined", procName, 1);
if ((lh->array = (void **)reallocNew((void **)&lh->array,
sizeof(void *) * lh->nalloc,
2 * sizeof(void *) * lh->nalloc)) == NULL)
return ERROR_INT("new ptr array not returned", procName, 1);
lh->nalloc = 2 * lh->nalloc;
return 0;
}
/*!
* lheapRemove()
*
* Input: lheap
* Return: ptr to item popped from the root of the heap,
* or null if the heap is empty or on error
*/
void *
lheapRemove(L_HEAP *lh)
{
void *item;
PROCNAME("lheapRemove");
if (!lh)
return (void *)ERROR_PTR("lh not defined", procName, NULL);
if (lh->n == 0)
return NULL;
item = lh->array[0];
lh->array[0] = lh->array[lh->n - 1]; /* move last to the head */
lh->array[lh->n - 1] = NULL; /* set ptr to null */
lh->n--;
lheapSwapDown(lh); /* restore the heap */
return item;
}
/*!
* lheapGetCount()
*
* Input: lheap
* Return: count, or 0 on error
*/
l_int32
lheapGetCount(L_HEAP *lh)
{
PROCNAME("lheapGetCount");
if (!lh)
return ERROR_INT("lh not defined", procName, 0);
return lh->n;
}
/*--------------------------------------------------------------------------*
* Heap operations *
*--------------------------------------------------------------------------*/
/*!
* lheapSwapUp()
*
* Input: lh (heap)
* index (of array corresponding to node to be swapped up)
* Return: 0 if OK, 1 on error
*
* Notes:
* (1) This is called after a new item is put on the heap, at the
* bottom of a complete tree.
* (2) To regain the heap order, we let it bubble up,
* iteratively swapping with its parent, until it either
* reaches the root of the heap or it finds a parent that
* is in the correct position already vis-a-vis the child.
*/
l_int32
lheapSwapUp(L_HEAP *lh,
l_int32 index)
{
l_int32 ip; /* index to heap for parent; 1 larger than array index */
l_int32 ic; /* index into heap for child */
l_float32 valp, valc;
PROCNAME("lheapSwapUp");
if (!lh)
return ERROR_INT("lh not defined", procName, 1);
if (index < 0 || index >= lh->n)
return ERROR_INT("invalid index", procName, 1);
ic = index + 1; /* index into heap: add 1 to array index */
if (lh->direction == L_SORT_INCREASING) {
while (1) {
if (ic == 1) /* root of heap */
break;
ip = ic / 2;
valc = *(l_float32 *)(lh->array[ic - 1]);
valp = *(l_float32 *)(lh->array[ip - 1]);
if (valp <= valc)
break;
SWAP_ITEMS(ip - 1, ic - 1);
ic = ip;
}
}
else { /* lh->direction == L_SORT_DECREASING */
while (1) {
if (ic == 1) /* root of heap */
break;
ip = ic / 2;
valc = *(l_float32 *)(lh->array[ic - 1]);
valp = *(l_float32 *)(lh->array[ip - 1]);
if (valp >= valc)
break;
SWAP_ITEMS(ip - 1, ic - 1);
ic = ip;
}
}
return 0;
}
/*!
* lheapSwapDown()
*
* Input: lh (heap)
* Return: 0 if OK, 1 on error
*
* Notes:
* (1) This is called after an item has been popped off the
* root of the heap, and the last item in the heap has
* been placed at the root.
* (2) To regain the heap order, we let it bubble down,
* iteratively swapping with one of its children. For a
* decreasing sort, it swaps with the largest child; for
* an increasing sort, the smallest. This continues until
* it either reaches the lowest level in the heap, or the
* parent finds that neither child should swap with it
* (e.g., for a decreasing heap, the parent is larger
* than or equal to both children).
*/
l_int32
lheapSwapDown(L_HEAP *lh)
{
l_int32 ip; /* index to heap for parent; 1 larger than array index */
l_int32 icr, icl; /* index into heap for left/right children */
l_float32 valp, valcl, valcr;
PROCNAME("lheapSwapDown");
if (!lh)
return ERROR_INT("lh not defined", procName, 1);
if (lheapGetCount(lh) < 1)
return 0;
ip = 1; /* index into top of heap: corresponds to array[0] */
if (lh->direction == L_SORT_INCREASING) {
while (1) {
icl = 2 * ip;
if (icl > lh->n)
break;
valp = *(l_float32 *)(lh->array[ip - 1]);
valcl = *(l_float32 *)(lh->array[icl - 1]);
icr = icl + 1;
if (icr > lh->n) { /* only a left child; no iters below */
if (valp > valcl)
SWAP_ITEMS(ip - 1, icl - 1);
break;
}
else { /* both children present; swap with the smallest if bigger */
valcr = *(l_float32 *)(lh->array[icr - 1]);
if (valp <= valcl && valp <= valcr) /* smaller than both */
break;
if (valcl <= valcr) { /* left smaller; swap */
SWAP_ITEMS(ip - 1, icl - 1);
ip = icl;
}
else { /* right smaller; swap */
SWAP_ITEMS(ip - 1, icr - 1);
ip = icr;
}
}
}
}
else { /* lh->direction == L_SORT_DECREASING */
while (1) {
icl = 2 * ip;
if (icl > lh->n)
break;
valp = *(l_float32 *)(lh->array[ip - 1]);
valcl = *(l_float32 *)(lh->array[icl - 1]);
icr = icl + 1;
if (icr > lh->n) { /* only a left child; no iters below */
if (valp < valcl)
SWAP_ITEMS(ip - 1, icl - 1);
break;
}
else { /* both children present; swap with the biggest if smaller */
valcr = *(l_float32 *)(lh->array[icr - 1]);
if (valp >= valcl && valp >= valcr) /* bigger than both */
break;
if (valcl >= valcr) { /* left bigger; swap */
SWAP_ITEMS(ip - 1, icl - 1);
ip = icl;
}
else { /* right bigger; swap */
SWAP_ITEMS(ip - 1, icr - 1);
ip = icr;
}
}
}
}
return 0;
}
/*!
* lheapSort()
*
* Input: lh (heap, with internal array)
* Return: 0 if OK, 1 on error
*
* Notes:
* (1) This sorts an array into heap order. If the heap is already
* in heap order for the direction given, this has no effect.
*/
l_int32
lheapSort(L_HEAP *lh)
{
l_int32 i;
PROCNAME("lheapSort");
if (!lh)
return ERROR_INT("lh not defined", procName, 1);
for (i = 0; i < lh->n; i++)
lheapSwapUp(lh, i);
return 0;
}
/*!
* lheapSortStrictOrder()
*
* Input: lh (heap, with internal array)
* Return: 0 if OK, 1 on error
*
* Notes:
* (1) This sorts a heap into strict order.
* (2) For each element, starting at the end of the array and
* working forward, the element is swapped with the head
* element and then allowed to swap down onto a heap of
* size reduced by one. The result is that the heap is
* reversed but in strict order. The array elements are
* then reversed to put it in the original order.
*/
l_int32
lheapSortStrictOrder(L_HEAP *lh)
{
l_int32 i, index, size;
PROCNAME("lheapSortStrictOrder");
if (!lh)
return ERROR_INT("lh not defined", procName, 1);
size = lh->n; /* save the actual size */
for (i = 0; i < size; i++) {
index = size - i;
SWAP_ITEMS(0, index - 1);
lh->n--; /* reduce the apparent heap size by 1 */
lheapSwapDown(lh);
}
lh->n = size; /* restore the size */
for (i = 0; i < size / 2; i++) /* reverse */
SWAP_ITEMS(i, size - i - 1);
return 0;
}
/*---------------------------------------------------------------------*
* Debug output *
*---------------------------------------------------------------------*/
/*!
* lheapPrint()
*
* Input: stream
* lheap
* Return: 0 if OK; 1 on error
*/
l_int32
lheapPrint(FILE *fp,
L_HEAP *lh)
{
l_int32 i;
PROCNAME("lheapPrint");
if (!fp)
return ERROR_INT("stream not defined", procName, 1);
if (!lh)
return ERROR_INT("lh not defined", procName, 1);
fprintf(fp, "\n L_Heap: nalloc = %d, n = %d, array = %p\n",
lh->nalloc, lh->n, lh->array);
for (i = 0; i < lh->n; i++)
fprintf(fp, "keyval[%d] = %f\n", i, *(l_float32 *)lh->array[i]);
return 0;
}