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/* Parse tree node implementation */
#include "Python.h"
#include "node.h"
#include "errcode.h"
node *
PyNode_New(int type)
{
node *n = (node *) PyObject_MALLOC(1 * sizeof(node));
if (n == NULL)
return NULL;
n->n_type = type;
n->n_str = NULL;
n->n_lineno = 0;
n->n_nchildren = 0;
n->n_child = NULL;
return n;
}
/* See comments at XXXROUNDUP below. Returns -1 on overflow. */
static int
fancy_roundup(int n)
{
/* Round up to the closest power of 2 >= n. */
int result = 256;
assert(n > 128);
while (result < n) {
result <<= 1;
if (result <= 0)
return -1;
}
return result;
}
/* A gimmick to make massive numbers of reallocs quicker. The result is
* a number >= the input. In PyNode_AddChild, it's used like so, when
* we're about to add child number current_size + 1:
*
* if XXXROUNDUP(current_size) < XXXROUNDUP(current_size + 1):
* allocate space for XXXROUNDUP(current_size + 1) total children
* else:
* we already have enough space
*
* Since a node starts out empty, we must have
*
* XXXROUNDUP(0) < XXXROUNDUP(1)
*
* so that we allocate space for the first child. One-child nodes are very
* common (presumably that would change if we used a more abstract form
* of syntax tree), so to avoid wasting memory it's desirable that
* XXXROUNDUP(1) == 1. That in turn forces XXXROUNDUP(0) == 0.
*
* Else for 2 <= n <= 128, we round up to the closest multiple of 4. Why 4?
* Rounding up to a multiple of an exact power of 2 is very efficient, and
* most nodes with more than one child have <= 4 kids.
*
* Else we call fancy_roundup() to grow proportionately to n. We've got an
* extreme case then (like test_longexp.py), and on many platforms doing
* anything less than proportional growth leads to exorbitant runtime
* (e.g., MacPython), or extreme fragmentation of user address space (e.g.,
* Win98).
*
* In a run of compileall across the 2.3a0 Lib directory, Andrew MacIntyre
* reported that, with this scheme, 89% of PyObject_REALLOC calls in
* PyNode_AddChild passed 1 for the size, and 9% passed 4. So this usually
* wastes very little memory, but is very effective at sidestepping
* platform-realloc disasters on vulnerable platforms.
*
* Note that this would be straightforward if a node stored its current
* capacity. The code is tricky to avoid that.
*/
#define XXXROUNDUP(n) ((n) <= 1 ? (n) : \
(n) <= 128 ? (((n) + 3) & ~3) : \
fancy_roundup(n))
int
PyNode_AddChild(register node *n1, int type, char *str, int lineno, int col_offset)
{
const int nch = n1->n_nchildren;
int current_capacity;
int required_capacity;
node *n;
if (nch == INT_MAX || nch < 0)
return E_OVERFLOW;
current_capacity = XXXROUNDUP(nch);
required_capacity = XXXROUNDUP(nch + 1);
if (current_capacity < 0 || required_capacity < 0)
return E_OVERFLOW;
if (current_capacity < required_capacity) {
n = n1->n_child;
n = (node *) PyObject_REALLOC(n,
required_capacity * sizeof(node));
if (n == NULL)
return E_NOMEM;
n1->n_child = n;
}
n = &n1->n_child[n1->n_nchildren++];
n->n_type = type;
n->n_str = str;
n->n_lineno = lineno;
n->n_col_offset = col_offset;
n->n_nchildren = 0;
n->n_child = NULL;
return 0;
}
/* Forward */
static void freechildren(node *);
void
PyNode_Free(node *n)
{
if (n != NULL) {
freechildren(n);
PyObject_FREE(n);
}
}
static void
freechildren(node *n)
{
int i;
for (i = NCH(n); --i >= 0; )
freechildren(CHILD(n, i));
if (n->n_child != NULL)
PyObject_FREE(n->n_child);
if (STR(n) != NULL)
PyObject_FREE(STR(n));
}
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