/* 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) {

if (required_capacity > PY_SIZE_MAX / sizeof(node)) {

return E_NOMEM;

}

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));

}