Chapter 3: Add implementation for Exercise 3-2

chapter-3/3.3-building-the-data-structure-in-c/strings.c

@@ -0,0 +1,47 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+enum
+{
+    STRINGS_SIZE = 1000,
+    _MULTIPLIER = 37,
+};
+
+typedef struct String String;
+struct String
+{
+    char *val;
+    String *next;
+};
+String *words[STRINGS_SIZE];
+
+int hash_string(char *val)
+{
+    int h = 0;
+    for (unsigned char *p = (unsigned char *)val; *p != '\0'; p++)
+        h = _MULTIPLIER * h + *p;
+
+    return h % STRINGS_SIZE;
+}
+
+String *lookup_string(char *val, int create)
+{
+    int h = hash_string(val);
+    for (String *s = words[h]; s != NULL; s = s->next)
+        if (strcmp(s->val, val) == 0)
+            return s;
+
+    if (create)
+    {
+        String *s = (String *)malloc(sizeof(String));
+        if (s == NULL)
+            return NULL;
+        s->val = val;
+        s->next = words[h];
+        words[h] = s;
+        return s;
+    }
+
+    return NULL;
+}