1
/* Parse tree node implementation */
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node *n = (node *) PyObject_MALLOC(1 * sizeof(node));
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/* See comments at XXXROUNDUP below. Returns -1 on overflow. */
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/* Round up to the closest power of 2 >= n. */
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/* A gimmick to make massive numbers of reallocs quicker. The result is
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* a number >= the input. In PyNode_AddChild, it's used like so, when
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* we're about to add child number current_size + 1:
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* if XXXROUNDUP(current_size) < XXXROUNDUP(current_size + 1):
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* allocate space for XXXROUNDUP(current_size + 1) total children
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* we already have enough space
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* Since a node starts out empty, we must have
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* XXXROUNDUP(0) < XXXROUNDUP(1)
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* so that we allocate space for the first child. One-child nodes are very
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* common (presumably that would change if we used a more abstract form
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* of syntax tree), so to avoid wasting memory it's desirable that
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* XXXROUNDUP(1) == 1. That in turn forces XXXROUNDUP(0) == 0.
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* Else for 2 <= n <= 128, we round up to the closest multiple of 4. Why 4?
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* Rounding up to a multiple of an exact power of 2 is very efficient, and
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* most nodes with more than one child have <= 4 kids.
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* Else we call fancy_roundup() to grow proportionately to n. We've got an
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* extreme case then (like test_longexp.py), and on many platforms doing
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* anything less than proportional growth leads to exorbitant runtime
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* (e.g., MacPython), or extreme fragmentation of user address space (e.g.,
64
* In a run of compileall across the 2.3a0 Lib directory, Andrew MacIntyre
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* reported that, with this scheme, 89% of PyObject_REALLOC calls in
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* PyNode_AddChild passed 1 for the size, and 9% passed 4. So this usually
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* wastes very little memory, but is very effective at sidestepping
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* platform-realloc disasters on vulnerable platforms.
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* Note that this would be straightforward if a node stored its current
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* capacity. The code is tricky to avoid that.
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#define XXXROUNDUP(n) ((n) <= 1 ? (n) : \
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(n) <= 128 ? _Py_SIZE_ROUND_UP((n), 4) : \
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PyNode_AddChild(node *n1, int type, char *str, int lineno, int col_offset)
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const int nch = n1->n_nchildren;
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int required_capacity;
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if (nch == INT_MAX || nch < 0)
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current_capacity = XXXROUNDUP(nch);
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required_capacity = XXXROUNDUP(nch + 1);
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if (current_capacity < 0 || required_capacity < 0)
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if (current_capacity < required_capacity) {
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if (required_capacity > PY_SIZE_MAX / sizeof(node)) {
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n = (node *) PyObject_REALLOC(n,
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required_capacity * sizeof(node));
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n = &n1->n_child[n1->n_nchildren++];
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n->n_lineno = lineno;
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n->n_col_offset = col_offset;
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static void freechildren(node *);
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static Py_ssize_t sizeofchildren(node *n);
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_PyNode_SizeOf(node *n)
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res = sizeof(node) + sizeofchildren(n);
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freechildren(node *n)
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for (i = NCH(n); --i >= 0; )
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freechildren(CHILD(n, i));
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if (n->n_child != NULL)
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PyObject_FREE(n->n_child);
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PyObject_FREE(STR(n));
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sizeofchildren(node *n)
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for (i = NCH(n); --i >= 0; )
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res += sizeofchildren(CHILD(n, i));
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if (n->n_child != NULL)
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/* allocated size of n->n_child array */
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res += XXXROUNDUP(NCH(n)) * sizeof(node);
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res += strlen(STR(n)) + 1;