/*
*   $Id: keyword.c,v 1.5 2003/07/17 03:08:23 darren Exp $
*
*   Copyright (c) 1998-2002, Darren Hiebert
*
*   This source code is released for free distribution under the terms of the
*   GNU General Public License.
*
*   Manages a keyword hash.
*/

/*
*   INCLUDE FILES
*/
#include "general.h"	/* must always come first */

#include <string.h>

#include "debug.h"
#include "keyword.h"
#include "options.h"
#include "routines.h"

/*
*   MACROS
*/
#define HASH_EXPONENT	7	/* must be less than 17 */

/*
*   DATA DECLARATIONS
*/
typedef struct sHashEntry {
    struct sHashEntry *next;
    const char *string;
    langType language;
    int value;
} hashEntry;

/*
*   DATA DEFINITIONS
*/
static const unsigned int TableSize = 1 << HASH_EXPONENT;
static hashEntry **HashTable = NULL;

/*
*   FUNCTION DEFINITIONS
*/

static hashEntry **getHashTable (void)
{
    static boolean allocated = FALSE;

    if (! allocated)
    {
	unsigned int i;

	HashTable = xMalloc (TableSize, hashEntry*);

	for (i = 0  ;  i < TableSize  ;  ++i)
	    HashTable [i] = NULL;

	allocated = TRUE;
    }
    return HashTable;
}

static hashEntry *getHashTableEntry (unsigned long hashedValue)
{
    hashEntry **const table = getHashTable ();
    hashEntry *entry;

    Assert (hashedValue < TableSize);
    entry = table [hashedValue];

    return entry;
}

static unsigned long hashValue (const char *const string)
{
    unsigned long value = 0;
    const unsigned char *p;

    Assert (string != NULL);

    /*  We combine the various words of the multiword key using the method
     *  described on page 512 of Vol. 3 of "The Art of Computer Programming".
     */
    for (p = (const unsigned char *) string  ;  *p != '\0'  ;  ++p)
    {
	value <<= 1;
	if (value & 0x00000100L)
	    value = (value & 0x000000ffL) + 1L;
	value ^= *p;
    }
    /*  Algorithm from page 509 of Vol. 3 of "The Art of Computer Programming"
     *  Treats "value" as a 16-bit integer plus 16-bit fraction.
     */
    value *= 40503L;		/* = 2^16 * 0.6180339887 ("golden ratio") */
    value &= 0x0000ffffL;	/* keep fractional part */
    value >>= 16 - HASH_EXPONENT; /* scale up by hash size and move down */

    return value;
}

static hashEntry *newEntry (const char *const string,
			    langType language, int value)
{
    hashEntry *const entry = xMalloc (1, hashEntry);

    entry->next     = NULL;
    entry->string   = string;
    entry->language = language;
    entry->value    = value;

    return entry;
}

/*  Note that it is assumed that a "value" of zero means an undefined keyword
 *  and clients of this function should observe this. Also, all keywords added
 *  should be added in lower case. If we encounter a case-sensitive language
 *  whose keywords are in upper case, we will need to redesign this.
 */
extern void addKeyword (const char *const string, langType language, int value)
{
    const unsigned long hashedValue = hashValue (string);
    hashEntry *tableEntry = getHashTableEntry (hashedValue);
    hashEntry *entry = tableEntry;

    if (entry == NULL)
    {
	hashEntry **const table = getHashTable ();
	table [hashedValue] = newEntry (string, language, value);
    }
    else
    {
	hashEntry *prev = NULL;

	while (entry != NULL)
	{
	    if (language == entry->language  &&
		strcmp (string, entry->string) == 0)
	    {
		Assert (("Already in table" == NULL));
	    }
	    prev = entry;
	    entry = entry->next;
	}
	if (entry == NULL)
	{
	    Assert (prev != NULL);
	    prev->next = newEntry (string, language, value);
	}
    }
}

extern int lookupKeyword (const char *const string, langType language)
{
    const unsigned long hashedValue = hashValue (string);
    hashEntry *entry = getHashTableEntry (hashedValue);
    int result = -1;

    while (entry != NULL)
    {
	if (language == entry->language  &&  strcmp (string, entry->string) == 0)
	{
	    result = entry->value;
	    break;
	}
	entry = entry->next;
    }
    return result;
}

extern void freeKeywordTable (void)
{
    if (HashTable != NULL)
    {
	unsigned int i;

	for (i = 0  ;  i < TableSize  ;  ++i)
	{
	    hashEntry *entry = HashTable [i];

	    while (entry != NULL)
	    {
		hashEntry *next = entry->next;
		eFree (entry);
		entry = next;
	    }
	}
	eFree (HashTable);
    }
}

#ifdef DEBUG

static void printEntry (const hashEntry *const entry)
{
    printf ("  %-15s %-7s\n", entry->string, getLanguageName (entry->language));
}

static unsigned int printBucket (const unsigned int i)
{
    hashEntry **const table = getHashTable ();
    hashEntry *entry = table [i];
    unsigned int measure = 1;
    boolean first = TRUE;

    printf ("%2d:", i);
    if (entry == NULL)
	printf ("\n");
    else while (entry != NULL)
    {
	if (! first)
	    printf ("    ");
	else
	{
	    printf (" ");
	    first = FALSE;
	}
	printEntry (entry);
	entry = entry->next;
	measure = 2 * measure;
    }
    return measure - 1;
}

extern void printKeywordTable (void)
{
    unsigned long emptyBucketCount = 0;
    unsigned long measure = 0;
    unsigned int i;

    for (i = 0  ;  i < TableSize  ;  ++i)
    {
	const unsigned int pass = printBucket (i);

	measure += pass;
	if (pass == 0)
	    ++emptyBucketCount;
    }

    printf ("spread measure = %ld\n", measure);
    printf ("%ld empty buckets\n", emptyBucketCount);
}

#endif

/* vi:set tabstop=8 shiftwidth=4: */
