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fix leftmost rotation

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This commit is contained in:
Alasdair Kergon 2010-04-22 13:18:27 +00:00
parent e8e7a84c64
commit cab2199de8
1 changed files with 38 additions and 23 deletions
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61
libdm/regex/parse_rx.c
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@ -16,6 +16,8 @@
#include "dmlib.h"
#include "parse_rx.h"
#include <ctype.h>
struct parse_sp { /* scratch pad for the parsing process */
struct dm_pool *mem;
int type; /* token type, 0 indicates a charset */
@ -413,24 +415,36 @@ static int _find_leftmost_common(struct rx_node *or,
return 0;
}
static struct rx_node *_exchange_nodes(struct dm_pool *mem, struct rx_node *r, struct rx_node *left_cat, struct rx_node *right_cat, unsigned leftmost)
/* If top node is OR, rotate from ((ab)|((ac)|d)) to (((ab)|(ac))|d) */
static int _rotate_ors(struct rx_node *r)
{
struct rx_node *new_r, *new_cat;
struct rx_node *old_r_right;
if (r->type == OR && r->right->type == OR) {
old_r_right = r->right;
r->right = old_r_right->right;
old_r_right->right = old_r_right->left;
old_r_right->left = r->left;
r->left = old_r_right;
return 1;
}
return 0;
}
static struct rx_node *_exchange_nodes(struct dm_pool *mem, struct rx_node *r,
struct rx_node *left_cat, struct rx_node *right_cat,
unsigned leftmost)
{
struct rx_node *new_r;
/* FIXME Clean up leftmost */
if (leftmost) {
new_r = r->right;
new_cat = _node(mem, CAT, left_cat->left, r);
if (!new_cat)
new_r = _node(mem, CAT, left_cat->left, r);
if (!new_r)
return_NULL;
new_r->left = new_cat;
memcpy(left_cat, left_cat->right, sizeof(*left_cat));
r->right = right_cat->right;
/* FIXME Avoid this */
if (new_r->right == right_cat->right)
new_r = new_r->left;
memcpy(right_cat, right_cat->right, sizeof(*right_cat));
} else {
new_r = _node(mem, CAT, r, right_cat->right);
if (!new_r)
@ -447,6 +461,8 @@ static struct rx_node *_pass(struct dm_pool *mem,
struct rx_node *r,
int *changed)
{
struct rx_node *left, *right;
/*
* walk the tree, optimising every 'or' node.
*/
@ -475,18 +491,17 @@ static struct rx_node *_pass(struct dm_pool *mem,
if (!(r->right = _pass(mem, r->right, changed)))
return_NULL;
{
struct rx_node *left, *right;
if (_find_leftmost_common(r, &left, &right, 1)) {
if (_find_leftmost_common(r, &left, &right, 1)) {
/*
* If rotate_ors changes the tree, left and right are stale,
* so just set 'changed' to repeat the search.
*/
if (!_rotate_ors(r))
r = _exchange_nodes(mem, r, left, right, 1);
*changed = 1;
} else if (_find_leftmost_common(r, &left, &right, 0)) {
r = _exchange_nodes(mem, r, left, right, 0);
*changed = 1;
}
*changed = 1;
} else if (_find_leftmost_common(r, &left, &right, 0)) {
r = _exchange_nodes(mem, r, left, right, 0);
*changed = 1;
}
break;