Initial commit

src/hash.c

@@ -0,0 +1,110 @@
+/*-----------------------------------------------------------------------------
+**   hash.c
+**
+**   Implementation of a simple Hash Table for string storage & retrieval
+**
+**   Written by L. Rossman
+**   Last Updated on 6/19/03
+**
+**   The hash table data structure (HTable) is defined in "hash.h".
+**   Interface Functions:
+**      HTcreate() - creates a hash table
+**      HTinsert() - inserts a string & its index value into a hash table
+**      HTfind()   - retrieves the index value of a string from a table
+**      HTfree()   - frees a hash table
+**
+*********************************************************************
+**   NOTE:  This is a modified version of the original HASH.C module.
+*********************************************************************
+*/
+
+#include <malloc.h>
+#include <string.h>
+#include "hash.h"
+
+/* Use Fletcher's checksum to compute 2-byte hash of string */
+unsigned int hash(char *str)
+{
+    unsigned int sum1= 0, check1;
+    unsigned long sum2= 0L;
+	while(  '\0' != *str  )
+    {
+        sum1 += (*str);
+        str++;
+        if (  255 <= sum1  ) sum1 -= 255;
+        sum2 += sum1;
+    }
+    check1= sum2;
+    check1 %= 255;
+    check1= 255 - (sum1+check1) % 255;
+    sum1= 255 - (sum1+check1) % 255;
+    return( ( ( check1 << 8 )  |  sum1  ) % HTMAXSIZE);
+}
+
+HTtable *HTcreate()
+{
+        int i;
+        HTtable *ht = (HTtable *) calloc(HTMAXSIZE, sizeof(HTtable));
+        if (ht != NULL) for (i=0; i<HTMAXSIZE; i++) ht[i] = NULL;
+        return(ht);
+}
+
+int     HTinsert(HTtable *ht, char *key, int data)
+{
+        unsigned int i = hash(key);
+        struct HTentry *entry;
+        if ( i >= HTMAXSIZE ) return(0);
+        entry = (struct HTentry *) malloc(sizeof(struct HTentry));
+        if (entry == NULL) return(0);
+        entry->key = key;
+        entry->data = data;
+        entry->next = ht[i];
+        ht[i] = entry;
+        return(1);
+}
+
+int     HTfind(HTtable *ht, char *key)
+{
+        unsigned int i = hash(key);
+        struct HTentry *entry;
+        if ( i >= HTMAXSIZE ) return(NOTFOUND);
+        entry = ht[i];
+        while (entry != NULL)
+        {
+            if ( strcmp(entry->key,key) == 0 ) return(entry->data);
+            entry = entry->next;
+        }
+        return(NOTFOUND);
+}
+
+char    *HTfindKey(HTtable *ht, char *key)
+{
+        unsigned int i = hash(key);
+        struct HTentry *entry;
+        if ( i >= HTMAXSIZE ) return(NULL);
+        entry = ht[i];
+        while (entry != NULL)
+        {
+            if ( strcmp(entry->key,key) == 0 ) return(entry->key);
+            entry = entry->next;
+        }
+        return(NULL);
+}
+
+void    HTfree(HTtable *ht)
+{
+        struct HTentry *entry,
+                       *nextentry;
+        int i;
+        for (i=0; i<HTMAXSIZE; i++)
+        {
+            entry = ht[i];
+            while (entry != NULL)
+            {
+                nextentry = entry->next;
+                free(entry);
+                entry = nextentry;
+            }
+        }
+        free(ht);
+}