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#include <stdlib.h>
#include <search.h>
#include "tsearch.h"
static inline int height(struct node *n) { return n ? n->h : 0; }
static int rot(void **p, struct node *x, int dir /* deeper side */)
{
struct node *y = x->a[dir];
struct node *z = y->a[!dir];
int hx = x->h;
int hz = height(z);
if (hz > height(y->a[dir])) {
/*
* x
* / \ dir z
* A y / \
* / \ --> x y
* z D /| |\
* / \ A B C D
* B C
*/
x->a[dir] = z->a[!dir];
y->a[!dir] = z->a[dir];
z->a[!dir] = x;
z->a[dir] = y;
x->h = hz;
y->h = hz;
z->h = hz+1;
} else {
/*
* x y
* / \ / \
* A y --> x D
* / \ / \
* z D A z
*/
x->a[dir] = z;
y->a[!dir] = x;
x->h = hz+1;
y->h = hz+2;
z = y;
}
*p = z;
return z->h - hx;
}
/* balance *p, return 0 if height is unchanged. */
int __tsearch_balance(void **p)
{
struct node *n = *p;
int h0 = height(n->a[0]);
int h1 = height(n->a[1]);
if (h0 - h1 + 1u < 3u) {
int old = n->h;
n->h = h0<h1 ? h1+1 : h0+1;
return n->h - old;
}
return rot(p, n, h0<h1);
}
void *tsearch(const void *key, void **rootp,
int (*cmp)(const void *, const void *))
{
if (!rootp)
return 0;
void **a[MAXH];
struct node *n = *rootp;
struct node *r;
int i=0;
a[i++] = rootp;
for (;;) {
if (!n)
break;
int c = cmp(key, n->key);
if (!c)
return n;
a[i++] = &n->a[c>0];
n = n->a[c>0];
}
r = malloc(sizeof *r);
if (!r)
return 0;
r->key = key;
r->a[0] = r->a[1] = 0;
r->h = 1;
/* insert new node, rebalance ancestors. */
*a[--i] = r;
while (i && __tsearch_balance(a[--i]));
return r;
}
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