tclhash.c

CMX990 demonstration board (DE9901)

/* 
 * tclHash.c --
 *
 *	Implementation of in-memory hash tables for Tcl and Tcl-based
 *	applications.
 *
 * Copyright 1991 Regents of the University of California
 * Permission to use, copy, modify, and distribute this
 * software and its documentation for any purpose and without
 * fee is hereby granted, provided that this copyright
 * notice appears in all copies.  The University of California
 * makes no representations about the suitability of this
 * software for any purpose.  It is provided "as is" without
 * express or implied warranty.
 *
 * $Id: tclHash.c,v 1.1.1.1 2001/04/29 20:34:51 karll Exp $
 */

#include "tclInt.h"

/*
 * Imported library procedures for which there are no header files:
 */

/*
 * When there are this many entries per bucket, on average, rebuild
 * the hash table to make it larger.
 */

#define REBUILD_MULTIPLIER	3


/*
 * The following macro takes a preliminary integer hash value and
 * produces an index into a hash tables bucket list.  The idea is
 * to make it so that preliminary values that are arbitrarily similar
 * will end up in different buckets.  The hash function was taken
 * from a random-number generator.
 */

#define RANDOM_INDEX(tablePtr, i) \
    (((((long) (i))*1103515245) >> (tablePtr)->downShift) & (tablePtr)->mask)

/*
 * Procedure prototypes for static procedures in this file:
 */

static Tcl_HashEntry *	ArrayFind _ANSI_ARGS_((Tcl_HashTable *tablePtr,
                                               char *key));
static Tcl_HashEntry *	ArrayCreate _ANSI_ARGS_((Tcl_HashTable *tablePtr,
                                                 char *key, int *newPtr));
static Tcl_HashEntry *	BogusFind _ANSI_ARGS_((Tcl_HashTable *tablePtr,
                                               char *key));
static Tcl_HashEntry *	BogusCreate _ANSI_ARGS_((Tcl_HashTable *tablePtr,
                                                 char *key, int *newPtr));
static unsigned int	HashString _ANSI_ARGS_((char *string));
static void		RebuildTable _ANSI_ARGS_((Tcl_HashTable *tablePtr));
static Tcl_HashEntry *	StringFind _ANSI_ARGS_((Tcl_HashTable *tablePtr,
                                                char *key));
static Tcl_HashEntry *	StringCreate _ANSI_ARGS_((Tcl_HashTable *tablePtr,
                                                  char *key, int *newPtr));
static Tcl_HashEntry *	OneWordFind _ANSI_ARGS_((Tcl_HashTable *tablePtr,
                                                 char *key));
static Tcl_HashEntry *	OneWordCreate _ANSI_ARGS_((Tcl_HashTable *tablePtr,
                                                   char *key, int *newPtr));

/*
 *----------------------------------------------------------------------
 *
 * Tcl_InitHashTable --
 *
 *	Given storage for a hash table, set up the fields to prepare
 *	the hash table for use.
 *
 * Results:
 *	None.
 *
 * Side effects:
 *	TablePtr is now ready to be passed to Tcl_FindHashEntry and
 *	Tcl_CreateHashEntry.
 *
 *----------------------------------------------------------------------
 */

void Tcl_InitHashTable(Tcl_HashTable *tablePtr, int keyType)
  //  register Tcl_HashTable *tablePtr;	/* Pointer to table record, which
  //					 * is supplied by the caller. */
  //int keyType;			/* Type of keys to use in table:
  //                                 * TCL_STRING_KEYS, TCL_ONE_WORD_KEYS,
  //                                 * or an integer >= 2. */
{
  tablePtr->buckets = tablePtr->staticBuckets;
  tablePtr->staticBuckets[0] = tablePtr->staticBuckets[1] = 0;
  tablePtr->staticBuckets[2] = tablePtr->staticBuckets[3] = 0;
  tablePtr->numBuckets = TCL_SMALL_HASH_TABLE;
  tablePtr->numEntries = 0;
  tablePtr->rebuildSize = TCL_SMALL_HASH_TABLE*REBUILD_MULTIPLIER;
  tablePtr->downShift = 28;
  tablePtr->mask = 3;
  tablePtr->keyType = keyType;
  if (keyType == TCL_STRING_KEYS) {
    tablePtr->findProc = StringFind;
    tablePtr->createProc = StringCreate;
  } else if (keyType == TCL_ONE_WORD_KEYS) {
    tablePtr->findProc = OneWordFind;
    tablePtr->createProc = OneWordCreate;
  } else {
    tablePtr->findProc = ArrayFind;
    tablePtr->createProc = ArrayCreate;
  };
}

/*
 *----------------------------------------------------------------------
 *
 * Tcl_DeleteHashEntry --
 *
 *	Remove a single entry from a hash table.
 *
 * Results:
 *	None.
 *
 * Side effects:
 *	The entry given by entryPtr is deleted from its table and
 *	should never again be used by the caller.  It is up to the
 *	caller to free the clientData field of the entry, if that
 *	is relevant.
 *
 *----------------------------------------------------------------------
 */

void Tcl_DeleteHashEntry(Tcl_HashEntry *entryPtr) {
  register Tcl_HashEntry *prevPtr;

  if (*entryPtr->bucketPtr == entryPtr) {
    *entryPtr->bucketPtr = entryPtr->nextPtr;
  } else {
    for (prevPtr = *entryPtr->bucketPtr; ; prevPtr = prevPtr->nextPtr) {
      if (prevPtr == NULL) {
        panic("malformed bucket chain in Tcl_DeleteHashEntry");
      }
      if (prevPtr->nextPtr == entryPtr) {
        prevPtr->nextPtr = entryPtr->nextPtr;
        break;
      }
    }
  }
  entryPtr->tablePtr->numEntries--;
  ckfree((char *) entryPtr);
}

/*
 *----------------------------------------------------------------------
 *
 * Tcl_DeleteHashTable --
 *
 *	Free up everything associated with a hash table except for
 *	the record for the table itself.
 *
 * Results:
 *	None.
 *
 * Side effects:
 *	The hash table is no longer useable.
 *
 *----------------------------------------------------------------------
 */

void Tcl_DeleteHashTable(Tcl_HashTable *tablePtr)
  //  register Tcl_HashTable *tablePtr;		/* Table to delete. */
{
  register Tcl_HashEntry *hPtr, *nextPtr;
  int i;

  /*
   * Free up all the entries in the table.
   */

  for (i = 0; i < tablePtr->numBuckets; i++) {
    hPtr = tablePtr->buckets[i];
    while (hPtr != NULL) {
      nextPtr = hPtr->nextPtr;
      ckfree((char *) hPtr);
      hPtr = nextPtr;
    }
  }

  /*
   * Free up the bucket array, if it was dynamically allocated.
   */

  if (tablePtr->buckets != tablePtr->staticBuckets) {
    ckfree((char *) tablePtr->buckets);
  }

  /*
   * Arrange for panics if the table is used again without
   * re-initialization.
   */

  tablePtr->findProc = BogusFind;
  tablePtr->createProc = BogusCreate;
}

/*
 *----------------------------------------------------------------------
 *
 * Tcl_FirstHashEntry --
 *
 *	Locate the first entry in a hash table and set up a record
 *	that can be used to step through all the remaining entries
 *	of the table.
 *
 * Results:
 *	The return value is a pointer to the first entry in tablePtr,
 *	or NULL if tablePtr has no entries in it.  The memory at
 *	*searchPtr is initialized so that subsequent calls to
 *	Tcl_NextHashEntry will return all of the entries in the table,
 *	one at a time.
 *
 * Side effects:
 *	None.
 *
 *----------------------------------------------------------------------
 */

Tcl_HashEntry *Tcl_FirstHashEntry(Tcl_HashTable *tablePtr, Tcl_HashSearch *searchPtr)
  //  Tcl_HashTable *tablePtr;		/* Table to search. */
  //Tcl_HashSearch *searchPtr;		/* Place to store information about
  //					 * progress through the table. */
{
  searchPtr->tablePtr = tablePtr;
  searchPtr->nextIndex = 0;
  searchPtr->nextEntryPtr = NULL;
  return Tcl_NextHashEntry(searchPtr);
}

/*
 *----------------------------------------------------------------------
 *
 * Tcl_NextHashEntry --
 *
 *	Once a hash table enumeration has been initiated by calling
 *	Tcl_FirstHashEntry, this procedure may be called to return
 *	successive elements of the table.
 *
 * Results:
 *	The return value is the next entry in the hash table being
 *	enumerated, or NULL if the end of the table is reached.
 *
 * Side effects:
 *	None.
 *
 *----------------------------------------------------------------------
 */

Tcl_HashEntry *Tcl_NextHashEntry(Tcl_HashSearch *searchPtr)
  //  register Tcl_HashSearch *searchPtr;	/* Place to store information about
  //					 * progress through the table.  Must
  //					 * have been initialized by calling
  //					 * Tcl_FirstHashEntry. */
{
  Tcl_HashEntry *hPtr;

  while (searchPtr->nextEntryPtr == NULL) {
    if (searchPtr->nextIndex >= searchPtr->tablePtr->numBuckets) {
      return NULL;
    }
    searchPtr->nextEntryPtr =
      searchPtr->tablePtr->buckets[searchPtr->nextIndex];
    searchPtr->nextIndex++;
  }
  hPtr = searchPtr->nextEntryPtr;
  searchPtr->nextEntryPtr = hPtr->nextPtr;
  return hPtr;
}

/*
 *----------------------------------------------------------------------
 *
 * Tcl_HashStats --
 *
 *	Return statistics describing the layout of the hash table
 *	in its hash buckets.
 *
 * Results:
 *	The return value is a malloc-ed string containing information
 *	about tablePtr.  It is the caller's responsibility to free
 *	this string.
 *
 * Side effects:
 *	None.
 *
 *----------------------------------------------------------------------
 */
char * Tcl_HashStats(Tcl_HashTable *tablePtr)
  //  Tcl_HashTable *tablePtr;		/* Table for which to produce stats. */
{
#define NUM_COUNTERS 10
  int count[NUM_COUNTERS], overflow, i, j;
  double average, tmp;
  register Tcl_HashEntry *hPtr;
  char *result, *p;

  /*
   * Compute a histogram of bucket usage.
   */

  for (i = 0; i < NUM_COUNTERS; i++) {
    count[i] = 0;
  }
  overflow = 0;
  average = 0.0;
  for (i = 0; i < tablePtr->numBuckets; i++) {
    j = 0;
    for (hPtr = tablePtr->buckets[i]; hPtr != NULL; hPtr = hPtr->nextPtr) {
      j++;
    }
    if (j < NUM_COUNTERS) {
      count[j]++;
    } else {
      overflow++;
    }
    tmp = j;
    average += (tmp+1.0)*(tmp/tablePtr->numEntries)/2.0;
  }

  /*
   * Print out the histogram and a few other pieces of information.
   */

  result = (char *) ckalloc((unsigned) ((NUM_COUNTERS*60) + 300));
  sprintf(result, "%d entries in table, %d buckets\n",
          tablePtr->numEntries, tablePtr->numBuckets);
  p = result + strlen(result);
  for (i = 0; i < NUM_COUNTERS; i++) {
    sprintf(p, "number of buckets with %d entries: %d\n",
            i, count[i]);
    p += strlen(p);
  }
  sprintf(p, "number of buckets with more %d or more entries: %d\n",
          NUM_COUNTERS, overflow);
  p += strlen(p);
  sprintf(p, "average search distance for entry: %.1f", average);
  return result;
}

/*
 *----------------------------------------------------------------------
 *
 * HashString --
 *
 *	Compute a one-word summary of a text string, which can be
 *	used to generate a hash index.
 *
 * Results:
 *	The return value is a one-word summary of the information in
 *	string.
 *
 * Side effects:
 *	None.
 *
 *----------------------------------------------------------------------
 */

static unsigned int HashString(char *string)
  //  register char *string;	/* String from which to compute hash value. */
{
  register unsigned int result;
  register int c;

  /*
   * I tried a zillion different hash functions and asked many other
   * people for advice.  Many people had their own favorite functions,
   * all different, but no-one had much idea why they were good ones.
   * I chose the one below (multiply by 9 and add new character)
   * because of the following reasons:
   *
   * 1. Multiplying by 10 is perfect for keys that are decimal strings,
   *    and multiplying by 9 is just about as good.
   * 2. Times-9 is (shift-left-3) plus (old).  This means that each
   *    character's bits hang around in the low-order bits of the
   *    hash value for ever, plus they spread fairly rapidly up to
   *    the high-order bits to fill out the hash value.  This seems
   *    works well both for decimal and non-decimal strings.
   */

  result = 0;
  while (1) {
    c = *string;
    string++;
    if (c == 0) {
      break;
    }
    result += (result<<3) + c;
  }
  return result;
}

/*
 *----------------------------------------------------------------------
 *
 * StringFind --
 *
 *	Given a hash table with string keys, and a string key, find
 *	the entry with a matching key.
 *
 * Results:
 *	The return value is a token for the matching entry in the
 *	hash table, or NULL if there was no matching entry.
 *
 * Side effects:
 *	None.
 *
 *----------------------------------------------------------------------
 */

static Tcl_HashEntry *StringFind(Tcl_HashTable *tablePtr, char *key)
  //  Tcl_HashTable *tablePtr;	/* Table in which to lookup entry. */
  //char *key;			/* Key to use to find matching entry. */
{
  register Tcl_HashEntry *hPtr;
  register char *p1, *p2;
  int index;

  index = HashString(key) & tablePtr->mask;

  /*
   * Search all of the entries in the appropriate bucket.
   */

  for (hPtr = tablePtr->buckets[index]; hPtr != NULL;
       hPtr = hPtr->nextPtr) {
    for (p1 = key, p2 = hPtr->key.string; ; p1++, p2++) {
      if (*p1 != *p2) {
        break;
      }
      if (*p1 == '\0') {
        return hPtr;
      }
    }
  }
  return NULL;
}

/*
 *----------------------------------------------------------------------
 *
 * StringCreate --
 *
 *	Given a hash table with string keys, and a string key, find
 *	the entry with a matching key.  If there is no matching entry,