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-rw-r--r--src/search/hsearch.c118
1 files changed, 118 insertions, 0 deletions
diff --git a/src/search/hsearch.c b/src/search/hsearch.c
new file mode 100644
index 00000000..be856b2a
--- /dev/null
+++ b/src/search/hsearch.c
@@ -0,0 +1,118 @@
+#include <stdlib.h>
+#include <string.h>
+#include <search.h>
+
+/*
+open addressing hash table with 2^n table size
+quadratic probing is used in case of hash collision
+tab indices and hash are size_t
+after resize fails with ENOMEM the state of tab is still usable
+
+with the posix api items cannot be iterated and length cannot be queried
+*/
+
+#define MINSIZE 8
+#define MAXSIZE ((size_t)-1/2 + 1)
+
+struct entry {
+ ENTRY item;
+ size_t hash;
+};
+
+static size_t mask;
+static size_t used;
+static struct entry *tab;
+
+static size_t keyhash(char *k)
+{
+ unsigned char *p = (void *)k;
+ size_t h = 0;
+
+ while (*p)
+ h = 31*h + *p++;
+ return h;
+}
+
+static int resize(size_t nel)
+{
+ size_t newsize;
+ size_t i, j;
+ struct entry *e, *newe;
+ struct entry *oldtab = tab;
+ struct entry *oldend = tab + mask + 1;
+
+ if (nel > MAXSIZE)
+ nel = MAXSIZE;
+ for (newsize = MINSIZE; newsize < nel; newsize *= 2);
+ tab = calloc(newsize, sizeof *tab);
+ if (!tab) {
+ tab = oldtab;
+ return 0;
+ }
+ mask = newsize - 1;
+ if (!oldtab)
+ return 1;
+ for (e = oldtab; e < oldend; e++)
+ if (e->item.key) {
+ for (i=e->hash,j=1; ; i+=j++) {
+ newe = tab + (i & mask);
+ if (!newe->item.key)
+ break;
+ }
+ *newe = *e;
+ }
+ free(oldtab);
+ return 1;
+}
+
+int hcreate(size_t nel)
+{
+ mask = 0;
+ used = 0;
+ tab = 0;
+ return resize(nel);
+}
+
+void hdestroy(void)
+{
+ free(tab);
+ tab = 0;
+ mask = 0;
+ used = 0;
+}
+
+static struct entry *lookup(char *key, size_t hash)
+{
+ size_t i, j;
+ struct entry *e;
+
+ for (i=hash,j=1; ; i+=j++) {
+ e = tab + (i & mask);
+ if (!e->item.key ||
+ (e->hash==hash && strcmp(e->item.key, key)==0))
+ break;
+ }
+ return e;
+}
+
+ENTRY *hsearch(ENTRY item, ACTION action)
+{
+ size_t hash = keyhash(item.key);
+ struct entry *e = lookup(item.key, hash);
+
+ if (e->item.key)
+ return &e->item;
+ if (action == FIND)
+ return 0;
+ e->item = item;
+ e->hash = hash;
+ if (++used > mask - mask/4) {
+ if (!resize(2*used)) {
+ used--;
+ e->item.key = 0;
+ return 0;
+ }
+ e = lookup(item.key, hash);
+ }
+ return &e->item;
+}