134 lines
3.4 KiB
C
134 lines
3.4 KiB
C
/* Parse tree node implementation */
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#include "Python.h"
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#include "node.h"
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#include "errcode.h"
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node *
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PyNode_New(int type)
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{
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node *n = PyMem_NEW(node, 1);
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if (n == NULL)
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return NULL;
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n->n_type = type;
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n->n_str = NULL;
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n->n_lineno = 0;
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n->n_nchildren = 0;
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n->n_child = NULL;
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return n;
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}
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/* See comments at XXXROUNDUP below. Returns -1 on overflow. */
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static int
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fancy_roundup(int n)
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{
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/* Round up to the closest power of 2 >= n. */
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int result = 256;
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assert(n > 128);
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while (result < n) {
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result <<= 1;
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if (result <= 0)
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return -1;
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}
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return result;
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}
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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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*
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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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* else:
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* we already have enough space
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*
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* Since a node starts out empty, we must have
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*
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* XXXROUNDUP(0) < XXXROUNDUP(1)
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*
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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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*
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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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*
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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.,
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* Win98).
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*
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* In a run of compileall across the 2.3a0 Lib directory, Andrew MacIntyre
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* reported that, with this scheme, 89% of PyMem_RESIZE 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 vulnernable platforms.
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*
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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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*/
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#define XXXROUNDUP(n) ((n) <= 1 ? (n) : \
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(n) <= 128 ? (((n) + 3) & ~3) : \
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fancy_roundup(n))
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int
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PyNode_AddChild(register node *n1, int type, char *str, int lineno)
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{
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const int nch = n1->n_nchildren;
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int current_capacity;
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int required_capacity;
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node *n;
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if (nch == INT_MAX || nch < 0)
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return E_OVERFLOW;
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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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return E_OVERFLOW;
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if (current_capacity < required_capacity) {
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n = n1->n_child;
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PyMem_RESIZE(n, node, required_capacity);
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if (n == NULL)
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return E_NOMEM;
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n1->n_child = n;
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}
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n = &n1->n_child[n1->n_nchildren++];
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n->n_type = type;
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n->n_str = str;
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n->n_lineno = lineno;
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n->n_nchildren = 0;
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n->n_child = NULL;
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return 0;
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}
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/* Forward */
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static void freechildren(node *);
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void
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PyNode_Free(node *n)
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{
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if (n != NULL) {
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freechildren(n);
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PyMem_DEL(n);
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}
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}
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static void
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freechildren(node *n)
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{
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int i;
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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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PyMem_DEL(n->n_child);
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if (STR(n) != NULL)
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PyMem_DEL(STR(n));
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}
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