Parser/node.c

/* Parse tree node implementation */

#include "Python.h"
#include "node.h"
#include "errcode.h"

node *
PyNode_New(int type)
{
	node *n = PyMem_NEW(node, 1);
	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. */
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;
	return result;
}

/* A gimmick to make massive numbers of reallocs quicker.  The result is
 * a number >= the input.  For n=0 we must return 0.
 * For n=1, we return 1, to avoid wasting memory in common 1-child nodes
 * (XXX are those actually common?).
 * Else for n <= 128, round up to the closest multiple of 4.  Why 4?
 * Rounding up to a multiple of an exact power of 2 is very efficient.
 * Else 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).
 * This would be straightforward if a node stored its current capacity.  The
 * code is tricky to avoid that.
 */
#define XXXROUNDUP(n) ((n) == 1 ? 1 : \
		       (n) <= 128 ? (((n) + 3) & ~3) : \
		       fancy_roundup(n))


int
PyNode_AddChild(register node *n1, int type, char *str, int lineno)
{
	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 < required_capacity) {
		n = n1->n_child;
		PyMem_RESIZE(n, node, required_capacity);
		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_nchildren = 0;
	n->n_child = NULL;
	return 0;
}

/* Forward */
static void freechildren(node *);


void
PyNode_Free(node *n)
{
	if (n != NULL) {
		freechildren(n);
		PyMem_DEL(n);
	}
}

static void
freechildren(node *n)
{
	int i;
	for (i = NCH(n); --i >= 0; )
		freechildren(CHILD(n, i));
	if (n->n_child != NULL)
		PyMem_DEL(n->n_child);
	if (STR(n) != NULL)
		PyMem_DEL(STR(n));
}