是一种特别的树结构,一般用于存放字符串。Critbit tree是一种,其树的深度为O(longest-length),有点像二叉树,不过对于字符串做分支检测的时候代价很小。
Crit-bit快速高效的支持下面的一些操作:
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插入一个字符串
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测试一个字符串是否在树里
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删除一个字符串
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查找出树中所有以某个字符串开始的所有字符串
在插入过程
然后再继续插入后的结构变化是:
代码基于varnish, 并添加列出相同prefix字符串功能
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#include <stdio.h>
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#include <stdlib.h>
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#include <stdio.h>
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#include <stdlib.h>
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#include <sys/types.h>
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#include <sys/time.h>
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#include <unistd.h>
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#include <unistd.h>
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#include <inttypes.h>
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/*---------------------------------------------------------------------
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* Table for finding out how many bits two bytes have in common sequentially,
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* counting from the MSB towards the LSB.
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* ie:
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* hcb_bittbl[0x01 ^ 0x22] == 2
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* hcb_bittbl[0x10 ^ 0x0b] == 3
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*
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*/
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#define DIGEST_LEN 32
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static unsigned char hcb_bittbl[256];
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static unsigned char hcb_bits(unsigned char x, unsigned char y)
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{
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return hcb_bittbl[x ^ y];
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}
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static void hcb_build_bittbl(void)
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{
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unsigned char x;
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unsigned y;
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y = 0;
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for (x = 0; x < 8; x++)
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for (; y < (1U << x); y++)
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hcb_bittbl[y] = 8 - x;
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}
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/*---------------------------------------------------------------------
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* For space reasons we overload the two pointers with two different
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* kinds of of pointers. We cast them to uintptr_t's and abuse the
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* low two bits to tell them apart, assuming that Varnish will never
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* run on machines with less than 32bit alignment.
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*
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* Asserts will explode if these assumptions are not met.
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*/
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struct hcb_y {
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unsigned short critbit;
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unsigned char ptr;
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unsigned char bitmask;
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volatile uintptr_t leaf[2];
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};
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#define HCB_BIT_NODE (1<<0)
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#define HCB_BIT_Y (1<<1)
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struct hcb_root {
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volatile uintptr_t origo;
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};
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static struct hcb_root hcb_root;
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/*---------------------------------------------------------------------
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* Pointer accessor functions
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*/
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static int hcb_is_node(uintptr_t u)
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{
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return (u & HCB_BIT_NODE);
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}
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static int hcb_is_y(uintptr_t u)
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{
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return (u & HCB_BIT_Y);
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}
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static uintptr_t hcb_r_node(uintptr_t n)
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{
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return (HCB_BIT_NODE | (uintptr_t)n);
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}
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static uintptr_t hcb_l_node(uintptr_t u)
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{
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return (u & ~HCB_BIT_NODE);
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}
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static uintptr_t hcb_r_y(struct hcb_y *y)
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{
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return (HCB_BIT_Y | (uintptr_t)y);
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}
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static struct hcb_y *hcb_l_y(uintptr_t u)
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{
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return ((struct hcb_y *)(u & ~HCB_BIT_Y));
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}
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/*---------------------------------------------------------------------
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* Find the "critical" bit that separates these two digests
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*/
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static unsigned hcb_crit_bit(const char *oh1, const char *oh2, struct hcb_y *y)
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{
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unsigned char u, r;
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for (u = 0; u < DIGEST_LEN && oh1[u] == oh2[u]; u++)
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;
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r = hcb_bits(oh1[u], oh2[u]);
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y->ptr = u;
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y->bitmask = 0x80 >> r;
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y->critbit = u * 8 + r;
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return (y->critbit);
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}
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/*---------------------------------------------------------------------
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* Unless we have the lock, we need to be very careful about pointer
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* references into the tree, we cannot trust things to be the same
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* in two consequtive memory accesses.
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*/
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static char *hcb_insert(struct hcb_root *root, char *oh)
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{
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volatile uintptr_t *p;
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uintptr_t pp;
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struct hcb_y *y, *y2;
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char *oh2;
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unsigned s, s2;
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p = &root->origo;
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pp = *p;
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if (pp == 0) {
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*p = hcb_r_node(oh);
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return (oh);
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}
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while(hcb_is_y(pp)) {
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y = hcb_l_y(pp);
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s = (oh[y->ptr] & y->bitmask) != 0;
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p = &y->leaf[s];
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pp = *p;
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}
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if (pp == 0) {
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/* We raced hcb_delete and got a NULL pointer */
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return (NULL);
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}
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/* We found a node, does it match ? */
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oh2 = hcb_l_node(pp);
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if (!memcmp(oh2, oh, DIGEST_LEN))
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return (oh2);
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/* Insert */
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y2 = (struct hcb_y *) malloc(sizeof(struct hcb_y));
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if(y2==NULL)
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return NULL;
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(void)hcb_crit_bit(oh, oh2, y2);
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s2 = (oh[y2->ptr] & y2->bitmask) != 0;
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y2->leaf[s2] = hcb_r_node(oh);
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s2 = 1-s2;
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p = &root->origo;
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while(hcb_is_y(*p)) {
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y = hcb_l_y(*p);
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if (y->critbit > y2->critbit)
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break;
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s = (oh[y->ptr] & y->bitmask) != 0;
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p = &y->leaf[s];
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}
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y2->leaf[s2] = *p;
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*p = hcb_r_y(y2);
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return(oh);
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}
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static void hcb_delete(struct hcb_root *r, char *oh)
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{
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struct hcb_y *y;
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volatile uintptr_t *p;
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unsigned s;
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if (r->origo == hcb_r_node(oh)) {
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r->origo = 0;
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return;
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}
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p = &r->origo;
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y = NULL;
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while(1) {
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y = hcb_l_y(*p);
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s = (oh[y->ptr] & y->bitmask) != 0;
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if (y->leaf[s] == hcb_r_node(oh)) {
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*p = y->leaf[1 - s];
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free(y);
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return;
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}
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p = &y->leaf[s];
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}
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}
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static void hcb_start(void)
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{
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memset(&hcb_root, 0, sizeof hcb_root);
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hcb_build_bittbl();
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}
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static char *hcb_lookup(struct hcb_root *root, char *noh)
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{
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volatile uintptr_t *p;
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uintptr_t pp;
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struct hcb_y *y, *y2;
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char *oh2;
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unsigned s, s2;
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p = &root->origo;
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pp = *p;
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if (pp == 0) {
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return NULL;
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}
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while(hcb_is_y(pp)) {
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y = hcb_l_y(pp);
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s = (noh[y->ptr] & y->bitmask) != 0;
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p = &y->leaf[s];
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pp = *p;
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}
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if (pp == 0) {
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/* We raced hcb_delete and got a NULL pointer */
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return (NULL);
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}
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/* We found a node, does it match ? */
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oh2 = hcb_l_node(pp);
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if (!memcmp(oh2, noh, DIGEST_LEN))
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return (oh2);
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return(NULL);
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}
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static void recur_print(uintptr_t pp)
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{
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if(pp==0)
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return;
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if( hcb_is_node(pp) )
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{
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char *oh2 = hcb_l_node(pp);
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printf("%sn", oh2);
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return;
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}
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else
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{
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struct hcb_y *y = hcb_l_y(pp);
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recur_print(y->leaf[0]);
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recur_print(y->leaf[1]);
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}
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}
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static char *hcb_get_prefix(struct hcb_root *root, char *prefix)
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{
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int prefix_len = strlen(prefix);
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if(prefix_len ==0)
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return NULL;
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volatile uintptr_t *p;
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uintptr_t pp;
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struct hcb_y *y, *y2;
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char *oh2;
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unsigned s, s2;
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p = &root->origo;
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pp = *p;
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if (pp == 0) {
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return NULL;
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}
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while(hcb_is_y(pp)) {
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y = hcb_l_y(pp);
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if(y->ptr >= prefix_len)
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break;
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s = (prefix[y->ptr] & y->bitmask) != 0;
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p = &y->leaf[s];
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pp = *p;
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}
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if (pp == 0) {
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/* We raced hcb_delete and got a NULL pointer */
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return (NULL);
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}
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recur_print(pp);
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return(NULL);
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}
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int main()
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{
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hcb_start();
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char t1[DIGEST_LEN] = "test";
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hcb_insert(&hcb_root, t1);
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char t2[DIGEST_LEN] = "test1";
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hcb_insert(&hcb_root, t2);
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char t3[DIGEST_LEN] = "test2";
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hcb_insert(&hcb_root, t3);
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int i = 0;
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while(i<100)
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{
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char *t4 = (char *)malloc(DIGEST_LEN);
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memset(t4, 0, DIGEST_LEN);
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sprintf(t4, "test%d", i);
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hcb_insert(&hcb_root, t4);
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i++;
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}
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if( hcb_lookup(&hcb_root, t1) )
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{
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printf("find itn");
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}
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else
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{
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printf("can not find itn");
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}
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printf("begin to deleten");
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hcb_delete(&hcb_root, t1);
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if( hcb_lookup(&hcb_root, t1) )
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{
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printf("find itn");
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}
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else
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{
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printf("can not find itn");
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}
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hcb_get_prefix(&hcb_root, "test");
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return 0;
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}
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