hash table in c

c-cpp/18_hashtable/hashtable.c

@@ -0,0 +1,186 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <stdbool.h>
+#include <string.h>
+#include <time.h>
+
+/* One implementation of hash table with linear probing. */
+
+#define HASH_SHIFT 4
+#define HASH_SIZE (1 << HASH_SHIFT)
+#define HASH_MASK (HASH_SIZE - 1)
+
+struct hash_table {
+	unsigned int  used;
+	unsigned long entry[HASH_SIZE];
+};
+
+void hash_table_reset(struct hash_table *table)
+{
+	int i;
+
+	table->used = 0;
+	for (i = 0; i < HASH_SIZE; i++)
+		table->entry[i] = ~0;
+}
+
+unsigned int hash_function(unsigned long value)
+{
+	return value & HASH_MASK;
+}
+
+void dump_hash_table(struct hash_table *table)
+{
+	int i;
+
+	for (i = 0; i < HASH_SIZE; i++) {
+		if (table->entry[i] == ~0)
+			printf("%2u:       nil \n", i);
+		else
+			printf("%2u:%10lu -> %2u\n",
+				i, table->entry[i],
+				hash_function(table->entry[i]));
+	}
+}
+
+void hash_function_test()
+{
+	int i;
+
+	srandom(time(NULL));
+
+	for (i = 0; i < 10; i++) {
+		unsigned long val = random();
+		printf("%10lu -> %2u\n", val, hash_function(val));;
+	}
+}
+
+unsigned int next_probe(unsigned int prev_key)
+{
+	return (prev_key + 1) & HASH_MASK;
+}
+
+void next_probe_test()
+{
+	int i;
+	unsigned int key1, key2;
+
+	key1 = 0;
+	for (i = 0; i < HASH_SIZE; i++) {
+		key2 = next_probe(key1);
+		printf("%2u -> %2u\n", key1, key2);
+		key1 = key2;
+	}
+}
+
+void hash_table_add(struct hash_table *table, unsigned long value)
+{
+	unsigned int key = hash_function(value);
+
+	if (table->used >= HASH_SIZE)
+		return;
+
+	while (table->entry[key] != ~0)
+		key = next_probe(key);
+
+	table->entry[key] = value;
+	table->used++;
+}
+
+unsigned int hash_table_slot(struct hash_table *table, unsigned long value)
+{
+	int i;
+	unsigned int key = hash_function(value);
+
+	for (i = 0; i < HASH_SIZE; i++) {
+		if (table->entry[key] == value || table->entry[key] == ~0)
+			break;
+		key = next_probe(key);
+	}
+
+	return key;
+}
+
+bool hash_table_find(struct hash_table *table, unsigned long value)
+{
+	return table->entry[hash_table_slot(table, value)] == value;
+}
+
+void hash_table_del(struct hash_table *table, unsigned long value)
+{
+	unsigned int i, j, k;
+
+	if (!hash_table_find(table, value))
+		return;
+
+	i = j = hash_table_slot(table, value);
+
+	while (true) {
+		table->entry[i] = ~0;
+
+		do {
+			j = next_probe(j);
+			if (table->entry[j] == ~0)
+				return;
+			k = hash_function(table->entry[j]);
+		} while ((i <= j) ? (i < k && k <= j) : (i < k || k <= j));
+
+		table->entry[i] = table->entry[j];
+		i = j;
+	}
+	table->used++;
+}
+
+void hash_table_add_test()
+{
+	struct hash_table table;
+
+	hash_table_reset(&table);
+	hash_table_add(&table, 87645);
+
+	printf("Table has%s 87645\n",
+		hash_table_find(&table, 87645) ? "":"n't");
+	printf("Table has%s 87647\n",
+		hash_table_find(&table, 87647) ? "":"n't");
+}
+
+void hash_table_del_test1()
+{
+	struct hash_table table;
+
+	hash_table_reset(&table);
+	hash_table_add(&table, 0x1ff0);
+	hash_table_add(&table, 0x2ff0);
+	hash_table_add(&table, 0x3ff0);
+	dump_hash_table(&table);
+
+	printf("=== Remove 0x1ff0\n");
+	hash_table_del(&table, 0x1ff0);
+	dump_hash_table(&table);
+}
+
+void hash_table_del_test2()
+{
+	struct hash_table table;
+
+	hash_table_reset(&table);
+	hash_table_add(&table, 0x1ff0);
+	hash_table_add(&table, 0x1ff1);
+	hash_table_add(&table, 0x1ff2);
+	hash_table_add(&table, 0x2ff0);
+	dump_hash_table(&table);
+
+	printf("=== Remove 0x1ff0\n");
+	hash_table_del(&table, 0x1ff0);
+	dump_hash_table(&table);
+}
+
+int main()
+{
+	//hash_function_test();
+	//next_probe_test();
+	//hash_table_add_test();
+	hash_table_del_test2();
+
+	return 0;
+}