First commit ~0,10

G/LIB/GIF_HASH.C

@@ -0,0 +1,155 @@
+/*****************************************************************************
+*   "Gif-Lib" - Yet another gif library.				     *
+*									     *
+* Written by:  Gershon Elber			IBM PC Ver 0.1,	Jun. 1989    *
+******************************************************************************
+* Module to support the following operations:				     *
+*									     *
+* 1. InitHashTable - initialize hash table.				     *
+* 2. ClearHashTable - clear the hash table to an empty state.		     *
+* 2. InsertHashTable - insert one item into data structure.		     *
+* 3. ExistsHashTable - test if item exists in data structure.		     *
+*									     *
+* This module is used to hash the GIF codes during encoding.		     *
+******************************************************************************
+* History:								     *
+* 14 Jun 89 - Version 1.0 by Gershon Elber.				     *
+*****************************************************************************/
+
+#ifdef __MSDOS__
+#include <io.h>
+#include <alloc.h>
+#include <sys\stat.h>
+#else
+#include <sys/types.h>
+#include <sys/stat.h>
+#endif /* __MSDOS__ */
+
+#include <fcntl.h>
+#include <stdio.h>
+#include <string.h>
+#include "gif_lib.h"
+#include "gif_hash.h"
+
+#define PROGRAM_NAME	"GIF_LIBRARY"
+
+/* #define  DEBUG_HIT_RATE    Debug number of misses per hash Insert/Exists. */
+
+#ifdef	DEBUG_HIT_RATE
+static long NumberOfTests = 0,
+	    NumberOfMisses = 0;
+#endif	/* DEBUG_HIT_RATE */
+
+#ifdef SYSV
+static char *VersionStr =
+        "Gif library module,\t\tGershon Elber\n\
+	(C) Copyright 1989 Gershon Elber, Non commercial use only.\n";
+#else
+static char *VersionStr =
+	PROGRAM_NAME
+	"	IBMPC "
+	GIF_LIB_VERSION
+	"	Gershon Elber,	"
+	__DATE__ ",   " __TIME__ "\n"
+	"(C) Copyright 1989 Gershon Elber, Non commercial use only.\n";
+#endif /* SYSV */
+
+static int KeyItem(unsigned long Item);
+
+/******************************************************************************
+* Initialize HashTable - allocate the memory needed and clear it.	      *
+******************************************************************************/
+GifHashTableType *_InitHashTable(void)
+{
+    GifHashTableType *HashTable;
+
+    if ((HashTable = (GifHashTableType *) malloc(sizeof(GifHashTableType)))
+	== NULL)
+	return NULL;
+
+    _ClearHashTable(HashTable);
+
+    return HashTable;
+}
+
+/******************************************************************************
+* Routine to clear the HashTable to an empty state.			      *
+* This part is a little machine depended. Use the commented part otherwise.   *
+******************************************************************************/
+void _ClearHashTable(GifHashTableType *HashTable)
+{
+    memset(HashTable -> HTable, 0xFF, HT_SIZE * sizeof(long));
+}
+
+/******************************************************************************
+* Routine to insert a new Item into the HashTable. The data is assumed to be  *
+* new one.								      *
+******************************************************************************/
+void _InsertHashTable(GifHashTableType *HashTable, unsigned long Key, int Code)
+{
+    int HKey = KeyItem(Key);
+    unsigned long *HTable = HashTable -> HTable;
+
+#ifdef DEBUG_HIT_RATE
+	NumberOfTests++;
+	NumberOfMisses++;
+#endif /* DEBUG_HIT_RATE */
+
+    while (HT_GET_KEY(HTable[HKey]) != 0xFFFFFL) {
+#ifdef DEBUG_HIT_RATE
+	    NumberOfMisses++;
+#endif /* DEBUG_HIT_RATE */
+	HKey = (HKey + 1) & HT_KEY_MASK;
+    }
+    HTable[HKey] = HT_PUT_KEY(Key) | HT_PUT_CODE(Code);
+}
+
+/******************************************************************************
+* Routine to test if given Key exists in HashTable and if so returns its code *
+* Returns the Code if key was found, -1 if not.				      *
+******************************************************************************/
+int _ExistsHashTable(GifHashTableType *HashTable, unsigned long Key)
+{
+    int HKey = KeyItem(Key);
+    unsigned long *HTable = HashTable -> HTable, HTKey;
+
+#ifdef DEBUG_HIT_RATE
+	NumberOfTests++;
+	NumberOfMisses++;
+#endif /* DEBUG_HIT_RATE */
+
+    while ((HTKey = HT_GET_KEY(HTable[HKey])) != 0xFFFFFL) {
+#ifdef DEBUG_HIT_RATE
+	    NumberOfMisses++;
+#endif /* DEBUG_HIT_RATE */
+	if (Key == HTKey) return HT_GET_CODE(HTable[HKey]);
+	HKey = (HKey + 1) & HT_KEY_MASK;
+    }
+
+    return -1;
+}
+
+/******************************************************************************
+* Routine to generate an HKey for the hashtable out of the given unique key.  *
+* The given Key is assumed to be 20 bits as follows: lower 8 bits are the     *
+* new postfix character, while the upper 12 bits are the prefix code.	      *
+* Because the average hit ratio is only 2 (2 hash references per entry),      *
+* evaluating more complex keys (such as twin prime keys) does not worth it!   *
+******************************************************************************/
+static int KeyItem(unsigned long Item)
+{
+    return ((Item >> 12) ^ Item) & HT_KEY_MASK;
+}
+
+#ifdef	DEBUG_HIT_RATE
+/******************************************************************************
+* Debugging routine to print the hit ratio - number of times the hash table   *
+* was tested per operation. This routine was used to test the KeyItem routine *
+******************************************************************************/
+void HashTablePrintHitRatio(void)
+{
+    printf("Hash Table Hit Ratio is %ld/%ld = %ld%%.\n",
+	NumberOfMisses, NumberOfTests,
+	NumberOfMisses * 100 / NumberOfTests);
+}
+#endif	/* DEBUG_HIT_RATE */