LCOV - code coverage report
Current view: | top level - Modules - _heapqmodule.c (source / functions) |  |  | Hit | Total | Coverage
Test: | CPython 3.12 LCOV report [commit 5e6661bce9] |  | Lines: | 6 | 227 | 2.6 %
Date: | 2023-03-20 08:15:36 |  | Functions: | 2 | 19 | 10.5 %
|  |  | Branches: | 1 | 88 | 1.1 %

               Branch data     Line data    Source code
           1                 :            : /* Drop in replacement for heapq.py
           2                 :            :
           3                 :            : C implementation derived directly from heapq.py in Py2.3
           4                 :            : which was written by Kevin O'Connor, augmented by Tim Peters,
           5                 :            : annotated by François Pinard, and converted to C by Raymond Hettinger.
           6                 :            :
           7                 :            : */
           8                 :            :
           9                 :            : #ifndef Py_BUILD_CORE_BUILTIN
          10                 :            : #  define Py_BUILD_CORE_MODULE 1
          11                 :            : #endif
          12                 :            :
          13                 :            : #include "Python.h"
          14                 :            : #include "pycore_list.h"          // _PyList_ITEMS()
          15                 :            :
          16                 :            : #include "clinic/_heapqmodule.c.h"
          17                 :            :
          18                 :            :
          19                 :            : /*[clinic input]
          20                 :            : module _heapq
          21                 :            : [clinic start generated code]*/
          22                 :            : /*[clinic end generated code: output=da39a3ee5e6b4b0d input=d7cca0a2e4c0ceb3]*/
          23                 :            :
          24                 :            : static int
          25                 :          0 : siftdown(PyListObject *heap, Py_ssize_t startpos, Py_ssize_t pos)
          26                 :            : {
          27                 :            :     PyObject *newitem, *parent, **arr;
          28                 :            :     Py_ssize_t parentpos, size;
          29                 :            :     int cmp;
          30                 :            :
          31                 :            :     assert(PyList_Check(heap));
          32                 :          0 :     size = PyList_GET_SIZE(heap);
          33         [ #  # ]:          0 :     if (pos >= size) {
          34                 :          0 :         PyErr_SetString(PyExc_IndexError, "index out of range");
          35                 :          0 :         return -1;
          36                 :            :     }
          37                 :            :
          38                 :            :     /* Follow the path to the root, moving parents down until finding
          39                 :            :        a place newitem fits. */
          40                 :          0 :     arr = _PyList_ITEMS(heap);
          41                 :          0 :     newitem = arr[pos];
          42         [ #  # ]:          0 :     while (pos > startpos) {
          43                 :          0 :         parentpos = (pos - 1) >> 1;
          44                 :          0 :         parent = arr[parentpos];
          45                 :          0 :         Py_INCREF(newitem);
          46                 :          0 :         Py_INCREF(parent);
          47                 :          0 :         cmp = PyObject_RichCompareBool(newitem, parent, Py_LT);
          48                 :          0 :         Py_DECREF(parent);
          49                 :          0 :         Py_DECREF(newitem);
          50         [ #  # ]:          0 :         if (cmp < 0)
          51                 :          0 :             return -1;
          52         [ #  # ]:          0 :         if (size != PyList_GET_SIZE(heap)) {
          53                 :          0 :             PyErr_SetString(PyExc_RuntimeError,
          54                 :            :                             "list changed size during iteration");
          55                 :          0 :             return -1;
          56                 :            :         }
          57         [ #  # ]:          0 :         if (cmp == 0)
          58                 :          0 :             break;
          59                 :          0 :         arr = _PyList_ITEMS(heap);
          60                 :          0 :         parent = arr[parentpos];
          61                 :          0 :         newitem = arr[pos];
          62                 :          0 :         arr[parentpos] = newitem;
          63                 :          0 :         arr[pos] = parent;
          64                 :          0 :         pos = parentpos;
          65                 :            :     }
          66                 :          0 :     return 0;
          67                 :            : }
          68                 :            :
          69                 :            : static int
          70                 :          0 : siftup(PyListObject *heap, Py_ssize_t pos)
          71                 :            : {
          72                 :            :     Py_ssize_t startpos, endpos, childpos, limit;
          73                 :            :     PyObject *tmp1, *tmp2, **arr;
          74                 :            :     int cmp;
          75                 :            :
          76                 :            :     assert(PyList_Check(heap));
          77                 :          0 :     endpos = PyList_GET_SIZE(heap);
          78                 :          0 :     startpos = pos;
          79         [ #  # ]:          0 :     if (pos >= endpos) {
          80                 :          0 :         PyErr_SetString(PyExc_IndexError, "index out of range");
          81                 :          0 :         return -1;
          82                 :            :     }
          83                 :            :
          84                 :            :     /* Bubble up the smaller child until hitting a leaf. */
          85                 :          0 :     arr = _PyList_ITEMS(heap);
          86                 :          0 :     limit = endpos >> 1;         /* smallest pos that has no child */
          87         [ #  # ]:          0 :     while (pos < limit) {
          88                 :            :         /* Set childpos to index of smaller child.   */
          89                 :          0 :         childpos = 2*pos + 1;    /* leftmost child position  */
          90         [ #  # ]:          0 :         if (childpos + 1 < endpos) {
          91                 :          0 :             PyObject* a = arr[childpos];
          92                 :          0 :             PyObject* b = arr[childpos + 1];
          93                 :          0 :             Py_INCREF(a);
          94                 :          0 :             Py_INCREF(b);
          95                 :          0 :             cmp = PyObject_RichCompareBool(a, b, Py_LT);
          96                 :          0 :             Py_DECREF(a);
          97                 :          0 :             Py_DECREF(b);
          98         [ #  # ]:          0 :             if (cmp < 0)
          99                 :          0 :                 return -1;
         100                 :          0 :             childpos += ((unsigned)cmp ^ 1);   /* increment when cmp==0 */
         101                 :          0 :             arr = _PyList_ITEMS(heap);         /* arr may have changed */
         102         [ #  # ]:          0 :             if (endpos != PyList_GET_SIZE(heap)) {
         103                 :          0 :                 PyErr_SetString(PyExc_RuntimeError,
         104                 :            :                                 "list changed size during iteration");
         105                 :          0 :                 return -1;
         106                 :            :             }
         107                 :            :         }
         108                 :            :         /* Move the smaller child up. */
         109                 :          0 :         tmp1 = arr[childpos];
         110                 :          0 :         tmp2 = arr[pos];
         111                 :          0 :         arr[childpos] = tmp2;
         112                 :          0 :         arr[pos] = tmp1;
         113                 :          0 :         pos = childpos;
         114                 :            :     }
         115                 :            :     /* Bubble it up to its final resting place (by sifting its parents down). */
         116                 :          0 :     return siftdown(heap, startpos, pos);
         117                 :            : }
         118                 :            :
         119                 :            : /*[clinic input]
         120                 :            : _heapq.heappush
         121                 :            :
         122                 :            :     heap: object(subclass_of='&PyList_Type')
         123                 :            :     item: object
         124                 :            :     /
         125                 :            :
         126                 :            : Push item onto heap, maintaining the heap invariant.
         127                 :            : [clinic start generated code]*/
         128                 :            :
         129                 :            : static PyObject *
         130                 :          0 : _heapq_heappush_impl(PyObject *module, PyObject *heap, PyObject *item)
         131                 :            : /*[clinic end generated code: output=912c094f47663935 input=7c69611f3698aceb]*/
         132                 :            : {
         133         [ #  # ]:          0 :     if (PyList_Append(heap, item))
         134                 :          0 :         return NULL;
         135                 :            :
         136         [ #  # ]:          0 :     if (siftdown((PyListObject *)heap, 0, PyList_GET_SIZE(heap)-1))
         137                 :          0 :         return NULL;
         138                 :          0 :     Py_RETURN_NONE;
         139                 :            : }
         140                 :            :
         141                 :            : static PyObject *
         142                 :          0 : heappop_internal(PyObject *heap, int siftup_func(PyListObject *, Py_ssize_t))
         143                 :            : {
         144                 :            :     PyObject *lastelt, *returnitem;
         145                 :            :     Py_ssize_t n;
         146                 :            :
         147                 :            :     /* raises IndexError if the heap is empty */
         148                 :          0 :     n = PyList_GET_SIZE(heap);
         149         [ #  # ]:          0 :     if (n == 0) {
         150                 :          0 :         PyErr_SetString(PyExc_IndexError, "index out of range");
         151                 :          0 :         return NULL;
         152                 :            :     }
         153                 :            :
         154                 :          0 :     lastelt = PyList_GET_ITEM(heap, n-1) ;
         155                 :          0 :     Py_INCREF(lastelt);
         156         [ #  # ]:          0 :     if (PyList_SetSlice(heap, n-1, n, NULL)) {
         157                 :          0 :         Py_DECREF(lastelt);
         158                 :          0 :         return NULL;
         159                 :            :     }
         160                 :          0 :     n--;
         161                 :            :
         162         [ #  # ]:          0 :     if (!n)
         163                 :          0 :         return lastelt;
         164                 :          0 :     returnitem = PyList_GET_ITEM(heap, 0);
         165                 :          0 :     PyList_SET_ITEM(heap, 0, lastelt);
         166         [ #  # ]:          0 :     if (siftup_func((PyListObject *)heap, 0)) {
         167                 :          0 :         Py_DECREF(returnitem);
         168                 :          0 :         return NULL;
         169                 :            :     }
         170                 :          0 :     return returnitem;
         171                 :            : }
         172                 :            :
         173                 :            : /*[clinic input]
         174                 :            : _heapq.heappop
         175                 :            :
         176                 :            :     heap: object(subclass_of='&PyList_Type')
         177                 :            :     /
         178                 :            :
         179                 :            : Pop the smallest item off the heap, maintaining the heap invariant.
         180                 :            : [clinic start generated code]*/
         181                 :            :
         182                 :            : static PyObject *
         183                 :          0 : _heapq_heappop_impl(PyObject *module, PyObject *heap)
         184                 :            : /*[clinic end generated code: output=96dfe82d37d9af76 input=91487987a583c856]*/
         185                 :            : {
         186                 :          0 :     return heappop_internal(heap, siftup);
         187                 :            : }
         188                 :            :
         189                 :            : static PyObject *
         190                 :          0 : heapreplace_internal(PyObject *heap, PyObject *item, int siftup_func(PyListObject *, Py_ssize_t))
         191                 :            : {
         192                 :            :     PyObject *returnitem;
         193                 :            :
         194         [ #  # ]:          0 :     if (PyList_GET_SIZE(heap) == 0) {
         195                 :          0 :         PyErr_SetString(PyExc_IndexError, "index out of range");
         196                 :          0 :         return NULL;
         197                 :            :     }
         198                 :            :
         199                 :          0 :     returnitem = PyList_GET_ITEM(heap, 0);
         200                 :          0 :     PyList_SET_ITEM(heap, 0, Py_NewRef(item));
         201         [ #  # ]:          0 :     if (siftup_func((PyListObject *)heap, 0)) {
         202                 :          0 :         Py_DECREF(returnitem);
         203                 :          0 :         return NULL;
         204                 :            :     }
         205                 :          0 :     return returnitem;
         206                 :            : }
         207                 :            :
         208                 :            :
         209                 :            : /*[clinic input]
         210                 :            : _heapq.heapreplace
         211                 :            :
         212                 :            :     heap: object(subclass_of='&PyList_Type')
         213                 :            :     item: object
         214                 :            :     /
         215                 :            :
         216                 :            : Pop and return the current smallest value, and add the new item.
         217                 :            :
         218                 :            : This is more efficient than heappop() followed by heappush(), and can be
         219                 :            : more appropriate when using a fixed-size heap.  Note that the value
         220                 :            : returned may be larger than item!  That constrains reasonable uses of
         221                 :            : this routine unless written as part of a conditional replacement:
         222                 :            :
         223                 :            :     if item > heap[0]:
         224                 :            :         item = heapreplace(heap, item)
         225                 :            : [clinic start generated code]*/
         226                 :            :
         227                 :            : static PyObject *
         228                 :          0 : _heapq_heapreplace_impl(PyObject *module, PyObject *heap, PyObject *item)
         229                 :            : /*[clinic end generated code: output=82ea55be8fbe24b4 input=719202ac02ba10c8]*/
         230                 :            : {
         231                 :          0 :     return heapreplace_internal(heap, item, siftup);
         232                 :            : }
         233                 :            :
         234                 :            : /*[clinic input]
         235                 :            : _heapq.heappushpop
         236                 :            :
         237                 :            :     heap: object(subclass_of='&PyList_Type')
         238                 :            :     item: object
         239                 :            :     /
         240                 :            :
         241                 :            : Push item on the heap, then pop and return the smallest item from the heap.
         242                 :            :
         243                 :            : The combined action runs more efficiently than heappush() followed by
         244                 :            : a separate call to heappop().
         245                 :            : [clinic start generated code]*/
         246                 :            :
         247                 :            : static PyObject *
         248                 :          0 : _heapq_heappushpop_impl(PyObject *module, PyObject *heap, PyObject *item)
         249                 :            : /*[clinic end generated code: output=67231dc98ed5774f input=5dc701f1eb4a4aa7]*/
         250                 :            : {
         251                 :            :     PyObject *returnitem;
         252                 :            :     int cmp;
         253                 :            :
         254         [ #  # ]:          0 :     if (PyList_GET_SIZE(heap) == 0) {
         255                 :          0 :         return Py_NewRef(item);
         256                 :            :     }
         257                 :            :
         258                 :          0 :     PyObject* top = PyList_GET_ITEM(heap, 0);
         259                 :          0 :     Py_INCREF(top);
         260                 :          0 :     cmp = PyObject_RichCompareBool(top, item, Py_LT);
         261                 :          0 :     Py_DECREF(top);
         262         [ #  # ]:          0 :     if (cmp < 0)
         263                 :          0 :         return NULL;
         264         [ #  # ]:          0 :     if (cmp == 0) {
         265                 :          0 :         return Py_NewRef(item);
         266                 :            :     }
         267                 :            :
         268         [ #  # ]:          0 :     if (PyList_GET_SIZE(heap) == 0) {
         269                 :          0 :         PyErr_SetString(PyExc_IndexError, "index out of range");
         270                 :          0 :         return NULL;
         271                 :            :     }
         272                 :            :
         273                 :          0 :     returnitem = PyList_GET_ITEM(heap, 0);
         274                 :          0 :     PyList_SET_ITEM(heap, 0, Py_NewRef(item));
         275         [ #  # ]:          0 :     if (siftup((PyListObject *)heap, 0)) {
         276                 :          0 :         Py_DECREF(returnitem);
         277                 :          0 :         return NULL;
         278                 :            :     }
         279                 :          0 :     return returnitem;
         280                 :            : }
         281                 :            :
         282                 :            : static Py_ssize_t
         283                 :          0 : keep_top_bit(Py_ssize_t n)
         284                 :            : {
         285                 :          0 :     int i = 0;
         286                 :            :
         287         [ #  # ]:          0 :     while (n > 1) {
         288                 :          0 :         n >>= 1;
         289                 :          0 :         i++;
         290                 :            :     }
         291                 :          0 :     return n << i;
         292                 :            : }
         293                 :            :
         294                 :            : /* Cache friendly version of heapify()
         295                 :            :    -----------------------------------
         296                 :            :
         297                 :            :    Build-up a heap in O(n) time by performing siftup() operations
         298                 :            :    on nodes whose children are already heaps.
         299                 :            :
         300                 :            :    The simplest way is to sift the nodes in reverse order from
         301                 :            :    n//2-1 to 0 inclusive.  The downside is that children may be
         302                 :            :    out of cache by the time their parent is reached.
         303                 :            :
         304                 :            :    A better way is to not wait for the children to go out of cache.
         305                 :            :    Once a sibling pair of child nodes have been sifted, immediately
         306                 :            :    sift their parent node (while the children are still in cache).
         307                 :            :
         308                 :            :    Both ways build child heaps before their parents, so both ways
         309                 :            :    do the exact same number of comparisons and produce exactly
         310                 :            :    the same heap.  The only difference is that the traversal
         311                 :            :    order is optimized for cache efficiency.
         312                 :            : */
         313                 :            :
         314                 :            : static PyObject *
         315                 :          0 : cache_friendly_heapify(PyObject *heap, int siftup_func(PyListObject *, Py_ssize_t))
         316                 :            : {
         317                 :            :     Py_ssize_t i, j, m, mhalf, leftmost;
         318                 :            :
         319                 :          0 :     m = PyList_GET_SIZE(heap) >> 1;         /* index of first childless node */
         320                 :          0 :     leftmost = keep_top_bit(m + 1) - 1;     /* leftmost node in row of m */
         321                 :          0 :     mhalf = m >> 1;                         /* parent of first childless node */
         322                 :            :
         323         [ #  # ]:          0 :     for (i = leftmost - 1 ; i >= mhalf ; i--) {
         324                 :          0 :         j = i;
         325                 :            :         while (1) {
         326         [ #  # ]:          0 :             if (siftup_func((PyListObject *)heap, j))
         327                 :          0 :                 return NULL;
         328         [ #  # ]:          0 :             if (!(j & 1))
         329                 :          0 :                 break;
         330                 :          0 :             j >>= 1;
         331                 :            :         }
         332                 :            :     }
         333                 :            :
         334         [ #  # ]:          0 :     for (i = m - 1 ; i >= leftmost ; i--) {
         335                 :          0 :         j = i;
         336                 :            :         while (1) {
         337         [ #  # ]:          0 :             if (siftup_func((PyListObject *)heap, j))
         338                 :          0 :                 return NULL;
         339         [ #  # ]:          0 :             if (!(j & 1))
         340                 :          0 :                 break;
         341                 :          0 :             j >>= 1;
         342                 :            :         }
         343                 :            :     }
         344                 :          0 :     Py_RETURN_NONE;
         345                 :            : }
         346                 :            :
         347                 :            : static PyObject *
         348                 :          0 : heapify_internal(PyObject *heap, int siftup_func(PyListObject *, Py_ssize_t))
         349                 :            : {
         350                 :            :     Py_ssize_t i, n;
         351                 :            :
         352                 :            :     /* For heaps likely to be bigger than L1 cache, we use the cache
         353                 :            :        friendly heapify function.  For smaller heaps that fit entirely
         354                 :            :        in cache, we prefer the simpler algorithm with less branching.
         355                 :            :     */
         356                 :          0 :     n = PyList_GET_SIZE(heap);
         357         [ #  # ]:          0 :     if (n > 2500)
         358                 :          0 :         return cache_friendly_heapify(heap, siftup_func);
         359                 :            :
         360                 :            :     /* Transform bottom-up.  The largest index there's any point to
         361                 :            :        looking at is the largest with a child index in-range, so must
         362                 :            :        have 2*i + 1 < n, or i < (n-1)/2.  If n is even = 2*j, this is
         363                 :            :        (2*j-1)/2 = j-1/2 so j-1 is the largest, which is n//2 - 1.  If
         364                 :            :        n is odd = 2*j+1, this is (2*j+1-1)/2 = j so j-1 is the largest,
         365                 :            :        and that's again n//2-1.
         366                 :            :     */
         367         [ #  # ]:          0 :     for (i = (n >> 1) - 1 ; i >= 0 ; i--)
         368         [ #  # ]:          0 :         if (siftup_func((PyListObject *)heap, i))
         369                 :          0 :             return NULL;
         370                 :          0 :     Py_RETURN_NONE;
         371                 :            : }
         372                 :            :
         373                 :            : /*[clinic input]
         374                 :            : _heapq.heapify
         375                 :            :
         376                 :            :     heap: object(subclass_of='&PyList_Type')
         377                 :            :     /
         378                 :            :
         379                 :            : Transform list into a heap, in-place, in O(len(heap)) time.
         380                 :            : [clinic start generated code]*/
         381                 :            :
         382                 :            : static PyObject *
         383                 :          0 : _heapq_heapify_impl(PyObject *module, PyObject *heap)
         384                 :            : /*[clinic end generated code: output=e63a636fcf83d6d0 input=53bb7a2166febb73]*/
         385                 :            : {
         386                 :          0 :     return heapify_internal(heap, siftup);
         387                 :            : }
         388                 :            :
         389                 :            : static int
         390                 :          0 : siftdown_max(PyListObject *heap, Py_ssize_t startpos, Py_ssize_t pos)
         391                 :            : {
         392                 :            :     PyObject *newitem, *parent, **arr;
         393                 :            :     Py_ssize_t parentpos, size;
         394                 :            :     int cmp;
         395                 :            :
         396                 :            :     assert(PyList_Check(heap));
         397                 :          0 :     size = PyList_GET_SIZE(heap);
         398         [ #  # ]:          0 :     if (pos >= size) {
         399                 :          0 :         PyErr_SetString(PyExc_IndexError, "index out of range");
         400                 :          0 :         return -1;
         401                 :            :     }
         402                 :            :
         403                 :            :     /* Follow the path to the root, moving parents down until finding
         404                 :            :        a place newitem fits. */
         405                 :          0 :     arr = _PyList_ITEMS(heap);
         406                 :          0 :     newitem = arr[pos];
         407         [ #  # ]:          0 :     while (pos > startpos) {
         408                 :          0 :         parentpos = (pos - 1) >> 1;
         409                 :          0 :         parent = Py_NewRef(arr[parentpos]);
         410                 :          0 :         Py_INCREF(newitem);
         411                 :          0 :         cmp = PyObject_RichCompareBool(parent, newitem, Py_LT);
         412                 :          0 :         Py_DECREF(parent);
         413                 :          0 :         Py_DECREF(newitem);
         414         [ #  # ]:          0 :         if (cmp < 0)
         415                 :          0 :             return -1;
         416         [ #  # ]:          0 :         if (size != PyList_GET_SIZE(heap)) {
         417                 :          0 :             PyErr_SetString(PyExc_RuntimeError,
         418                 :            :                             "list changed size during iteration");
         419                 :          0 :             return -1;
         420                 :            :         }
         421         [ #  # ]:          0 :         if (cmp == 0)
         422                 :          0 :             break;
         423                 :          0 :         arr = _PyList_ITEMS(heap);
         424                 :          0 :         parent = arr[parentpos];
         425                 :          0 :         newitem = arr[pos];
         426                 :          0 :         arr[parentpos] = newitem;
         427                 :          0 :         arr[pos] = parent;
         428                 :          0 :         pos = parentpos;
         429                 :            :     }
         430                 :          0 :     return 0;
         431                 :            : }
         432                 :            :
         433                 :            : static int
         434                 :          0 : siftup_max(PyListObject *heap, Py_ssize_t pos)
         435                 :            : {
         436                 :            :     Py_ssize_t startpos, endpos, childpos, limit;
         437                 :            :     PyObject *tmp1, *tmp2, **arr;
         438                 :            :     int cmp;
         439                 :            :
         440                 :            :     assert(PyList_Check(heap));
         441                 :          0 :     endpos = PyList_GET_SIZE(heap);
         442                 :          0 :     startpos = pos;
         443         [ #  # ]:          0 :     if (pos >= endpos) {
         444                 :          0 :         PyErr_SetString(PyExc_IndexError, "index out of range");
         445                 :          0 :         return -1;
         446                 :            :     }
         447                 :            :
         448                 :            :     /* Bubble up the smaller child until hitting a leaf. */
         449                 :          0 :     arr = _PyList_ITEMS(heap);
         450                 :          0 :     limit = endpos >> 1;         /* smallest pos that has no child */
         451         [ #  # ]:          0 :     while (pos < limit) {
         452                 :            :         /* Set childpos to index of smaller child.   */
         453                 :          0 :         childpos = 2*pos + 1;    /* leftmost child position  */
         454         [ #  # ]:          0 :         if (childpos + 1 < endpos) {
         455                 :          0 :             PyObject* a = arr[childpos + 1];
         456                 :          0 :             PyObject* b = arr[childpos];
         457                 :          0 :             Py_INCREF(a);
         458                 :          0 :             Py_INCREF(b);
         459                 :          0 :             cmp = PyObject_RichCompareBool(a, b, Py_LT);
         460                 :          0 :             Py_DECREF(a);
         461                 :          0 :             Py_DECREF(b);
         462         [ #  # ]:          0 :             if (cmp < 0)
         463                 :          0 :                 return -1;
         464                 :          0 :             childpos += ((unsigned)cmp ^ 1);   /* increment when cmp==0 */
         465                 :          0 :             arr = _PyList_ITEMS(heap);         /* arr may have changed */
         466         [ #  # ]:          0 :             if (endpos != PyList_GET_SIZE(heap)) {
         467                 :          0 :                 PyErr_SetString(PyExc_RuntimeError,
         468                 :            :                                 "list changed size during iteration");
         469                 :          0 :                 return -1;
         470                 :            :             }
         471                 :            :         }
         472                 :            :         /* Move the smaller child up. */
         473                 :          0 :         tmp1 = arr[childpos];
         474                 :          0 :         tmp2 = arr[pos];
         475                 :          0 :         arr[childpos] = tmp2;
         476                 :          0 :         arr[pos] = tmp1;
         477                 :          0 :         pos = childpos;
         478                 :            :     }
         479                 :            :     /* Bubble it up to its final resting place (by sifting its parents down). */
         480                 :          0 :     return siftdown_max(heap, startpos, pos);
         481                 :            : }
         482                 :            :
         483                 :            :
         484                 :            : /*[clinic input]
         485                 :            : _heapq._heappop_max
         486                 :            :
         487                 :            :     heap: object(subclass_of='&PyList_Type')
         488                 :            :     /
         489                 :            :
         490                 :            : Maxheap variant of heappop.
         491                 :            : [clinic start generated code]*/
         492                 :            :
         493                 :            : static PyObject *
         494                 :          0 : _heapq__heappop_max_impl(PyObject *module, PyObject *heap)
         495                 :            : /*[clinic end generated code: output=9e77aadd4e6a8760 input=362c06e1c7484793]*/
         496                 :            : {
         497                 :          0 :     return heappop_internal(heap, siftup_max);
         498                 :            : }
         499                 :            :
         500                 :            : /*[clinic input]
         501                 :            : _heapq._heapreplace_max
         502                 :            :
         503                 :            :     heap: object(subclass_of='&PyList_Type')
         504                 :            :     item: object
         505                 :            :     /
         506                 :            :
         507                 :            : Maxheap variant of heapreplace.
         508                 :            : [clinic start generated code]*/
         509                 :            :
         510                 :            : static PyObject *
         511                 :          0 : _heapq__heapreplace_max_impl(PyObject *module, PyObject *heap,
         512                 :            :                              PyObject *item)
         513                 :            : /*[clinic end generated code: output=8ad7545e4a5e8adb input=f2dd27cbadb948d7]*/
         514                 :            : {
         515                 :          0 :     return heapreplace_internal(heap, item, siftup_max);
         516                 :            : }
         517                 :            :
         518                 :            : /*[clinic input]
         519                 :            : _heapq._heapify_max
         520                 :            :
         521                 :            :     heap: object(subclass_of='&PyList_Type')
         522                 :            :     /
         523                 :            :
         524                 :            : Maxheap variant of heapify.
         525                 :            : [clinic start generated code]*/
         526                 :            :
         527                 :            : static PyObject *
         528                 :          0 : _heapq__heapify_max_impl(PyObject *module, PyObject *heap)
         529                 :            : /*[clinic end generated code: output=2cb028beb4a8b65e input=c1f765ee69f124b8]*/
         530                 :            : {
         531                 :          0 :     return heapify_internal(heap, siftup_max);
         532                 :            : }
         533                 :            :
         534                 :            : static PyMethodDef heapq_methods[] = {
         535                 :            :     _HEAPQ_HEAPPUSH_METHODDEF
         536                 :            :     _HEAPQ_HEAPPUSHPOP_METHODDEF
         537                 :            :     _HEAPQ_HEAPPOP_METHODDEF
         538                 :            :     _HEAPQ_HEAPREPLACE_METHODDEF
         539                 :            :     _HEAPQ_HEAPIFY_METHODDEF
         540                 :            :     _HEAPQ__HEAPPOP_MAX_METHODDEF
         541                 :            :     _HEAPQ__HEAPIFY_MAX_METHODDEF
         542                 :            :     _HEAPQ__HEAPREPLACE_MAX_METHODDEF
         543                 :            :     {NULL, NULL}           /* sentinel */
         544                 :            : };
         545                 :            :
         546                 :            : PyDoc_STRVAR(module_doc,
         547                 :            : "Heap queue algorithm (a.k.a. priority queue).\n\
         548                 :            : \n\
         549                 :            : Heaps are arrays for which a[k] <= a[2*k+1] and a[k] <= a[2*k+2] for\n\
         550                 :            : all k, counting elements from 0.  For the sake of comparison,\n\
         551                 :            : non-existing elements are considered to be infinite.  The interesting\n\
         552                 :            : property of a heap is that a[0] is always its smallest element.\n\
         553                 :            : \n\
         554                 :            : Usage:\n\
         555                 :            : \n\
         556                 :            : heap = []            # creates an empty heap\n\
         557                 :            : heappush(heap, item) # pushes a new item on the heap\n\
         558                 :            : item = heappop(heap) # pops the smallest item from the heap\n\
         559                 :            : item = heap[0]       # smallest item on the heap without popping it\n\
         560                 :            : heapify(x)           # transforms list into a heap, in-place, in linear time\n\
         561                 :            : item = heapreplace(heap, item) # pops and returns smallest item, and adds\n\
         562                 :            :                                # new item; the heap size is unchanged\n\
         563                 :            : \n\
         564                 :            : Our API differs from textbook heap algorithms as follows:\n\
         565                 :            : \n\
         566                 :            : - We use 0-based indexing.  This makes the relationship between the\n\
         567                 :            :   index for a node and the indexes for its children slightly less\n\
         568                 :            :   obvious, but is more suitable since Python uses 0-based indexing.\n\
         569                 :            : \n\
         570                 :            : - Our heappop() method returns the smallest item, not the largest.\n\
         571                 :            : \n\
         572                 :            : These two make it possible to view the heap as a regular Python list\n\
         573                 :            : without surprises: heap[0] is the smallest item, and heap.sort()\n\
         574                 :            : maintains the heap invariant!\n");
         575                 :            :
         576                 :            :
         577                 :            : PyDoc_STRVAR(__about__,
         578                 :            : "Heap queues\n\
         579                 :            : \n\
         580                 :            : [explanation by Fran\xc3\xa7ois Pinard]\n\
         581                 :            : \n\
         582                 :            : Heaps are arrays for which a[k] <= a[2*k+1] and a[k] <= a[2*k+2] for\n\
         583                 :            : all k, counting elements from 0.  For the sake of comparison,\n\
         584                 :            : non-existing elements are considered to be infinite.  The interesting\n\
         585                 :            : property of a heap is that a[0] is always its smallest element.\n"
         586                 :            : "\n\
         587                 :            : The strange invariant above is meant to be an efficient memory\n\
         588                 :            : representation for a tournament.  The numbers below are `k', not a[k]:\n\
         589                 :            : \n\
         590                 :            :                                    0\n\
         591                 :            : \n\
         592                 :            :                   1                                 2\n\
         593                 :            : \n\
         594                 :            :           3               4                5               6\n\
         595                 :            : \n\
         596                 :            :       7       8       9       10      11      12      13      14\n\
         597                 :            : \n\
         598                 :            :     15 16   17 18   19 20   21 22   23 24   25 26   27 28   29 30\n\
         599                 :            : \n\
         600                 :            : \n\
         601                 :            : In the tree above, each cell `k' is topping `2*k+1' and `2*k+2'.  In\n\
         602                 :            : a usual binary tournament we see in sports, each cell is the winner\n\
         603                 :            : over the two cells it tops, and we can trace the winner down the tree\n\
         604                 :            : to see all opponents s/he had.  However, in many computer applications\n\
         605                 :            : of such tournaments, we do not need to trace the history of a winner.\n\
         606                 :            : To be more memory efficient, when a winner is promoted, we try to\n\
         607                 :            : replace it by something else at a lower level, and the rule becomes\n\
         608                 :            : that a cell and the two cells it tops contain three different items,\n\
         609                 :            : but the top cell \"wins\" over the two topped cells.\n"
         610                 :            : "\n\
         611                 :            : If this heap invariant is protected at all time, index 0 is clearly\n\
         612                 :            : the overall winner.  The simplest algorithmic way to remove it and\n\
         613                 :            : find the \"next\" winner is to move some loser (let's say cell 30 in the\n\
         614                 :            : diagram above) into the 0 position, and then percolate this new 0 down\n\
         615                 :            : the tree, exchanging values, until the invariant is re-established.\n\
         616                 :            : This is clearly logarithmic on the total number of items in the tree.\n\
         617                 :            : By iterating over all items, you get an O(n ln n) sort.\n"
         618                 :            : "\n\
         619                 :            : A nice feature of this sort is that you can efficiently insert new\n\
         620                 :            : items while the sort is going on, provided that the inserted items are\n\
         621                 :            : not \"better\" than the last 0'th element you extracted.  This is\n\
         622                 :            : especially useful in simulation contexts, where the tree holds all\n\
         623                 :            : incoming events, and the \"win\" condition means the smallest scheduled\n\
         624                 :            : time.  When an event schedule other events for execution, they are\n\
         625                 :            : scheduled into the future, so they can easily go into the heap.  So, a\n\
         626                 :            : heap is a good structure for implementing schedulers (this is what I\n\
         627                 :            : used for my MIDI sequencer :-).\n"
         628                 :            : "\n\
         629                 :            : Various structures for implementing schedulers have been extensively\n\
         630                 :            : studied, and heaps are good for this, as they are reasonably speedy,\n\
         631                 :            : the speed is almost constant, and the worst case is not much different\n\
         632                 :            : than the average case.  However, there are other representations which\n\
         633                 :            : are more efficient overall, yet the worst cases might be terrible.\n"
         634                 :            : "\n\
         635                 :            : Heaps are also very useful in big disk sorts.  You most probably all\n\
         636                 :            : know that a big sort implies producing \"runs\" (which are pre-sorted\n\
         637                 :            : sequences, which size is usually related to the amount of CPU memory),\n\
         638                 :            : followed by a merging passes for these runs, which merging is often\n\
         639                 :            : very cleverly organised[1].  It is very important that the initial\n\
         640                 :            : sort produces the longest runs possible.  Tournaments are a good way\n\
         641                 :            : to that.  If, using all the memory available to hold a tournament, you\n\
         642                 :            : replace and percolate items that happen to fit the current run, you'll\n\
         643                 :            : produce runs which are twice the size of the memory for random input,\n\
         644                 :            : and much better for input fuzzily ordered.\n"
         645                 :            : "\n\
         646                 :            : Moreover, if you output the 0'th item on disk and get an input which\n\
         647                 :            : may not fit in the current tournament (because the value \"wins\" over\n\
         648                 :            : the last output value), it cannot fit in the heap, so the size of the\n\
         649                 :            : heap decreases.  The freed memory could be cleverly reused immediately\n\
         650                 :            : for progressively building a second heap, which grows at exactly the\n\
         651                 :            : same rate the first heap is melting.  When the first heap completely\n\
         652                 :            : vanishes, you switch heaps and start a new run.  Clever and quite\n\
         653                 :            : effective!\n\
         654                 :            : \n\
         655                 :            : In a word, heaps are useful memory structures to know.  I use them in\n\
         656                 :            : a few applications, and I think it is good to keep a `heap' module\n\
         657                 :            : around. :-)\n"
         658                 :            : "\n\
         659                 :            : --------------------\n\
         660                 :            : [1] The disk balancing algorithms which are current, nowadays, are\n\
         661                 :            : more annoying than clever, and this is a consequence of the seeking\n\
         662                 :            : capabilities of the disks.  On devices which cannot seek, like big\n\
         663                 :            : tape drives, the story was quite different, and one had to be very\n\
         664                 :            : clever to ensure (far in advance) that each tape movement will be the\n\
         665                 :            : most effective possible (that is, will best participate at\n\
         666                 :            : \"progressing\" the merge).  Some tapes were even able to read\n\
         667                 :            : backwards, and this was also used to avoid the rewinding time.\n\
         668                 :            : Believe me, real good tape sorts were quite spectacular to watch!\n\
         669                 :            : From all times, sorting has always been a Great Art! :-)\n");
         670                 :            :
         671                 :            :
         672                 :            : static int
         673                 :          3 : heapq_exec(PyObject *m)
         674                 :            : {
         675                 :          3 :     PyObject *about = PyUnicode_FromString(__about__);
         676         [ -  + ]:          3 :     if (PyModule_AddObject(m, "__about__", about) < 0) {
         677                 :          0 :         Py_DECREF(about);
         678                 :          0 :         return -1;
         679                 :            :     }
         680                 :          3 :     return 0;
         681                 :            : }
         682                 :            :
         683                 :            : static struct PyModuleDef_Slot heapq_slots[] = {
         684                 :            :     {Py_mod_exec, heapq_exec},
         685                 :            :     {0, NULL}
         686                 :            : };
         687                 :            :
         688                 :            : static struct PyModuleDef _heapqmodule = {
         689                 :            :     PyModuleDef_HEAD_INIT,
         690                 :            :     "_heapq",
         691                 :            :     module_doc,
         692                 :            :     0,
         693                 :            :     heapq_methods,
         694                 :            :     heapq_slots,
         695                 :            :     NULL,
         696                 :            :     NULL,
         697                 :            :     NULL
         698                 :            : };
         699                 :            :
         700                 :            : PyMODINIT_FUNC
         701                 :          3 : PyInit__heapq(void)
         702                 :            : {
         703                 :          3 :     return PyModuleDef_Init(&_heapqmodule);
         704                 :            : }

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