path: root/mysys/hash.c

/* Copyright (C) 2000 MySQL AB

   This program is free software; you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
   the Free Software Foundation; either version 2 of the License, or
   (at your option) any later version.

   This program is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU General Public License for more details.

   You should have received a copy of the GNU General Public License
   along with this program; if not, write to the Free Software
   Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA */

/* The hash functions used for saveing keys */
/* One of key_length or key_length_offset must be given */
/* Key length of 0 isn't allowed */

#include "mysys_priv.h"
#include <m_string.h>
#include <m_ctype.h>
#include "hash.h"

#define NO_RECORD	((uint) -1)
#define LOWFIND 1
#define LOWUSED 2
#define HIGHFIND 4
#define HIGHUSED 8

typedef struct st_hash_info {
  uint next;					/* index to next key */
  byte *data;					/* data for current entry */
} HASH_LINK;

static uint hash_mask(uint hashnr,uint buffmax,uint maxlength);
static void movelink(HASH_LINK *array,uint pos,uint next_link,uint newlink);
static int hashcmp(const HASH *hash, HASH_LINK *pos, const byte *key,
                   uint length);

static uint calc_hash(const HASH *hash, const byte *key, uint length)
{
  ulong nr1=1, nr2=4;
  hash->charset->coll->hash_sort(hash->charset,(uchar*) key,length,&nr1,&nr2);
  return nr1;
}

my_bool
_hash_init(HASH *hash,CHARSET_INFO *charset,
	   uint size,uint key_offset,uint key_length,
	   hash_get_key get_key,
	   void (*free_element)(void*),uint flags CALLER_INFO_PROTO)
{
  DBUG_ENTER("hash_init");
  DBUG_PRINT("enter",("hash: 0x%lx  size: %d", (long) hash, size));

  hash->records=0;
  if (my_init_dynamic_array_ci(&hash->array,sizeof(HASH_LINK),size,0))
  {
    hash->free=0;				/* Allow call to hash_free */
    DBUG_RETURN(1);
  }
  hash->key_offset=key_offset;
  hash->key_length=key_length;
  hash->blength=1;
  hash->get_key=get_key;
  hash->free=free_element;
  hash->flags=flags;
  hash->charset=charset;
  DBUG_RETURN(0);
}


/*
  Call hash->free on all elements in hash.

  SYNOPSIS
    hash_free_elements()
    hash   hash table

  NOTES:
    Sets records to 0
*/

static inline void hash_free_elements(HASH *hash)
{
  if (hash->free)
  {
    HASH_LINK *data=dynamic_element(&hash->array,0,HASH_LINK*);
    HASH_LINK *end= data + hash->records;
    while (data < end)
      (*hash->free)((data++)->data);
  }
  hash->records=0;
}


/*
  Free memory used by hash.

  SYNOPSIS
    hash_free()
    hash   the hash to delete elements of

  NOTES: Hash can't be reused without calling hash_init again.
*/

void hash_free(HASH *hash)
{
  DBUG_ENTER("hash_free");
  DBUG_PRINT("enter",("hash: 0x%lx", (long) hash));

  hash_free_elements(hash);
  hash->free= 0;
  delete_dynamic(&hash->array);
  DBUG_VOID_RETURN;
}


/*
  Delete all elements from the hash (the hash itself is to be reused).

  SYNOPSIS
    my_hash_reset()
    hash   the hash to delete elements of
*/

void my_hash_reset(HASH *hash)
{
  DBUG_ENTER("my_hash_reset");
  DBUG_PRINT("enter",("hash: 0x%lxd", (long) hash));

  hash_free_elements(hash);
  reset_dynamic(&hash->array);
  /* Set row pointers so that the hash can be reused at once */
  hash->blength= 1;
  DBUG_VOID_RETURN;
}

	/* some helper functions */

/*
  This function is char* instead of byte* as HPUX11 compiler can't
  handle inline functions that are not defined as native types
*/

static inline char*
hash_key(const HASH *hash, const byte *record, uint *length,
         my_bool first)
{
  if (hash->get_key)
    return (*hash->get_key)(record,length,first);
  *length=hash->key_length;
  return (byte*) record+hash->key_offset;
}

	/* Calculate pos according to keys */

static uint hash_mask(uint hashnr,uint buffmax,uint maxlength)
{
  if ((hashnr & (buffmax-1)) < maxlength) return (hashnr & (buffmax-1));
  return (hashnr & ((buffmax >> 1) -1));
}

static uint hash_rec_mask(const HASH *hash, HASH_LINK *pos,
                          uint buffmax, uint maxlength)
{
  uint length;
  byte *key= (byte*) hash_key(hash,pos->data,&length,0);
  return hash_mask(calc_hash(hash,key,length),buffmax,maxlength);
}



/* for compilers which can not handle inline */
static
#if !defined(__USLC__) && !defined(__sgi)
inline
#endif
unsigned int rec_hashnr(HASH *hash,const byte *record)
{
  uint length;
  byte *key= (byte*) hash_key(hash,record,&length,0);
  return calc_hash(hash,key,length);
}


gptr hash_search(const HASH *hash, const byte *key, uint length)
{
  HASH_SEARCH_STATE state;
  return hash_first(hash, key, length, &state);
}

/*
  Search after a record based on a key

  NOTE
   Assigns the number of the found record to HASH_SEARCH_STATE state
*/

gptr hash_first(const HASH *hash, const byte *key, uint length,
                HASH_SEARCH_STATE *current_record)
{
  HASH_LINK *pos;
  uint flag,idx;
  DBUG_ENTER("hash_first");

  flag=1;
  if (hash->records)
  {
    idx=hash_mask(calc_hash(hash,key,length ? length : hash->key_length),
		    hash->blength,hash->records);
    do
    {
      pos= dynamic_element(&hash->array,idx,HASH_LINK*);
      if (!hashcmp(hash,pos,key,length))
      {
	DBUG_PRINT("exit",("found key at %d",idx));
	*current_record= idx;
	DBUG_RETURN (pos->data);
      }
      if (flag)
      {
	flag=0;					/* Reset flag */
	if (hash_rec_mask(hash,pos,hash->blength,hash->records) != idx)
	  break;				/* Wrong link */
      }
    }
    while ((idx=pos->next) != NO_RECORD);
  }
  *current_record= NO_RECORD;
  DBUG_RETURN(0);
}

	/* Get next record with identical key */
	/* Can only be called if previous calls was hash_search */

gptr hash_next(const HASH *hash, const byte *key, uint length,
               HASH_SEARCH_STATE *current_record)
{
  HASH_LINK *pos;
  uint idx;

  if (*current_record != NO_RECORD)
  {
    HASH_LINK *data=dynamic_element(&hash->array,0,HASH_LINK*);
    for (idx=data[*current_record].next; idx != NO_RECORD ; idx=pos->next)
    {
      pos=data+idx;
      if (!hashcmp(hash,pos,key,length))
      {
	*current_record= idx;
	return pos->data;
      }
    }
    *current_record= NO_RECORD;
  }
  return 0;
}


	/* Change link from pos to new_link */

static void movelink(HASH_LINK *array,uint find,uint next_link,uint newlink)
{
  HASH_LINK *old_link;
  do
  {
    old_link=array+next_link;
  }
  while ((next_link=old_link->next) != find);
  old_link->next= newlink;
  return;
}

/*
  Compare a key in a record to a whole key. Return 0 if identical

  SYNOPSIS
    hashcmp()
    hash   hash table
    pos    position of hash record to use in comparison
    key    key for comparison
    length length of key

  NOTES:
    If length is 0, comparison is done using the length of the
    record being compared against.

  RETURN
    = 0  key of record == key
    != 0 key of record != key
 */

static int hashcmp(const HASH *hash, HASH_LINK *pos, const byte *key,
                   uint length)
{
  uint rec_keylength;
  byte *rec_key= (byte*) hash_key(hash,pos->data,&rec_keylength,1);
  return ((length && length != rec_keylength) ||
	  my_strnncoll(hash->charset, (uchar*) rec_key, rec_keylength,
		       (uchar*) key, rec_keylength));
}


	/* Write a hash-key to the hash-index */

my_bool my_hash_insert(HASH *info,const byte *record)
{
  int flag;
  uint halfbuff,hash_nr,first_index,idx;
  byte *ptr_to_rec,*ptr_to_rec2;
  HASH_LINK *data,*empty,*gpos,*gpos2,*pos;

  LINT_INIT(gpos); LINT_INIT(gpos2);
  LINT_INIT(ptr_to_rec); LINT_INIT(ptr_to_rec2);

  flag=0;
  if (!(empty=(HASH_LINK*) alloc_dynamic(&info->array)))
    return(TRUE);				/* No more memory */

  data=dynamic_element(&info->array,0,HASH_LINK*);
  halfbuff= info->blength >> 1;

  idx=first_index=info->records-halfbuff;
  if (idx != info->records)				/* If some records */
  {
    do
    {
      pos=data+idx;
      hash_nr=rec_hashnr(info,pos->data);
      if (flag == 0)				/* First loop; Check if ok */
	if (hash_mask(hash_nr,info->blength,info->records) != first_index)
	  break;
      if (!(hash_nr & halfbuff))
      {						/* Key will not move */
	if (!(flag & LOWFIND))
	{
	  if (flag & HIGHFIND)
	  {
	    flag=LOWFIND | HIGHFIND;
	    /* key shall be moved to the current empty position */
	    gpos=empty;
	    ptr_to_rec=pos->data;
	    empty=pos;				/* This place is now free */
	  }
	  else
	  {
	    flag=LOWFIND | LOWUSED;		/* key isn't changed */
	    gpos=pos;
	    ptr_to_rec=pos->data;
	  }
	}
	else
	{
	  if (!(flag & LOWUSED))
	  {
	    /* Change link of previous LOW-key */
	    gpos->data=ptr_to_rec;
	    gpos->next=(uint) (pos-data);
	    flag= (flag & HIGHFIND) | (LOWFIND | LOWUSED);
	  }
	  gpos=pos;
	  ptr_to_rec=pos->data;
	}
      }
      else
      {						/* key will be moved */
	if (!(flag & HIGHFIND))
	{
	  flag= (flag & LOWFIND) | HIGHFIND;
	  /* key shall be moved to the last (empty) position */
	  gpos2 = empty; empty=pos;
	  ptr_to_rec2=pos->data;
	}
	else
	{
	  if (!(flag & HIGHUSED))
	  {
	    /* Change link of previous hash-key and save */
	    gpos2->data=ptr_to_rec2;
	    gpos2->next=(uint) (pos-data);
	    flag= (flag & LOWFIND) | (HIGHFIND | HIGHUSED);
	  }
	  gpos2=pos;
	  ptr_to_rec2=pos->data;
	}
      }
    }
    while ((idx=pos->next) != NO_RECORD);

    if ((flag & (LOWFIND | LOWUSED)) == LOWFIND)
    {
      gpos->data=ptr_to_rec;
      gpos->next=NO_RECORD;
    }
    if ((flag & (HIGHFIND | HIGHUSED)) == HIGHFIND)
    {
      gpos2->data=ptr_to_rec2;
      gpos2->next=NO_RECORD;
    }
  }
  /* Check if we are at the empty position */

  idx=hash_mask(rec_hashnr(info,record),info->blength,info->records+1);
  pos=data+idx;
  if (pos == empty)
  {
    pos->data=(byte*) record;
    pos->next=NO_RECORD;
  }
  else
  {
    /* Check if more records in same hash-nr family */
    empty[0]=pos[0];
    gpos=data+hash_rec_mask(info,pos,info->blength,info->records+1);
    if (pos == gpos)
    {
      pos->data=(byte*) record;
      pos->next=(uint) (empty - data);
    }
    else
    {
      pos->data=(byte*) record;
      pos->next=NO_RECORD;
      movelink(data,(uint) (pos-data),(uint) (gpos-data),(uint) (empty-data));
    }
  }
  if (++info->records == info->blength)
    info->blength+= info->blength;
  return(0);
}


/******************************************************************************
** Remove one record from hash-table. The record with the same record
** ptr is removed.
** if there is a free-function it's called for record if found
******************************************************************************/

my_bool hash_delete(HASH *hash,byte *record)
{
  uint blength,pos2,pos_hashnr,lastpos_hashnr,idx,empty_index;
  HASH_LINK *data,*lastpos,*gpos,*pos,*pos3,*empty;
  DBUG_ENTER("hash_delete");
  if (!hash->records)
    DBUG_RETURN(1);

  blength=hash->blength;
  data=dynamic_element(&hash->array,0,HASH_LINK*);
  /* Search after record with key */
  pos=data+ hash_mask(rec_hashnr(hash,record),blength,hash->records);
  gpos = 0;

  while (pos->data != record)
  {
    gpos=pos;
    if (pos->next == NO_RECORD)
      DBUG_RETURN(1);			/* Key not found */
    pos=data+pos->next;
  }

  if ( --(hash->records) < hash->blength >> 1) hash->blength>>=1;
  lastpos=data+hash->records;

  /* Remove link to record */
  empty=pos; empty_index=(uint) (empty-data);
  if (gpos)
    gpos->next=pos->next;		/* unlink current ptr */
  else if (pos->next != NO_RECORD)
  {
    empty=data+(empty_index=pos->next);
    pos->data=empty->data;
    pos->next=empty->next;
  }

  if (empty == lastpos)			/* last key at wrong pos or no next link */
    goto exit;

  /* Move the last key (lastpos) */
  lastpos_hashnr=rec_hashnr(hash,lastpos->data);
  /* pos is where lastpos should be */
  pos=data+hash_mask(lastpos_hashnr,hash->blength,hash->records);
  if (pos == empty)			/* Move to empty position. */
  {
    empty[0]=lastpos[0];
    goto exit;
  }
  pos_hashnr=rec_hashnr(hash,pos->data);
  /* pos3 is where the pos should be */
  pos3= data+hash_mask(pos_hashnr,hash->blength,hash->records);
  if (pos != pos3)
  {					/* pos is on wrong posit */
    empty[0]=pos[0];			/* Save it here */
    pos[0]=lastpos[0];			/* This should be here */
    movelink(data,(uint) (pos-data),(uint) (pos3-data),empty_index);
    goto exit;
  }
  pos2= hash_mask(lastpos_hashnr,blength,hash->records+1);
  if (pos2 == hash_mask(pos_hashnr,blength,hash->records+1))
  {					/* Identical key-positions */
    if (pos2 != hash->records)
    {
      empty[0]=lastpos[0];
      movelink(data,(uint) (lastpos-data),(uint) (pos-data),empty_index);
      goto exit;
    }
    idx= (uint) (pos-data);		/* Link pos->next after lastpos */
  }
  else idx= NO_RECORD;		/* Different positions merge */

  empty[0]=lastpos[0];
  movelink(data,idx,empty_index,pos->next);
  pos->next=empty_index;

exit:
  VOID(pop_dynamic(&hash->array));
  if (hash->free)
    (*hash->free)((byte*) record);
  DBUG_RETURN(0);
}

	/*
	  Update keys when record has changed.
	  This is much more efficent than using a delete & insert.
	  */

my_bool hash_update(HASH *hash,byte *record,byte *old_key,uint old_key_length)
{
  uint idx,new_index,new_pos_index,blength,records,empty;
  HASH_LINK org_link,*data,*previous,*pos;
  DBUG_ENTER("hash_update");

  data=dynamic_element(&hash->array,0,HASH_LINK*);
  blength=hash->blength; records=hash->records;

  /* Search after record with key */

  idx=hash_mask(calc_hash(hash, old_key,(old_key_length ?
					      old_key_length :
					      hash->key_length)),
		  blength,records);
  new_index=hash_mask(rec_hashnr(hash,record),blength,records);
  if (idx == new_index)
    DBUG_RETURN(0);			/* Nothing to do (No record check) */
  previous=0;
  for (;;)
  {

    if ((pos= data+idx)->data == record)
      break;
    previous=pos;
    if ((idx=pos->next) == NO_RECORD)
      DBUG_RETURN(1);			/* Not found in links */
  }
  org_link= *pos;
  empty=idx;

  /* Relink record from current chain */

  if (!previous)
  {
    if (pos->next != NO_RECORD)
    {
      empty=pos->next;
      *pos= data[pos->next];
    }
  }
  else
    previous->next=pos->next;		/* unlink pos */

  /* Move data to correct position */
  pos=data+new_index;
  new_pos_index=hash_rec_mask(hash,pos,blength,records);
  if (new_index != new_pos_index)
  {					/* Other record in wrong position */
    data[empty] = *pos;
    movelink(data,new_index,new_pos_index,empty);
    org_link.next=NO_RECORD;
    data[new_index]= org_link;
  }
  else
  {					/* Link in chain at right position */
    org_link.next=data[new_index].next;
    data[empty]=org_link;
    data[new_index].next=empty;
  }
  DBUG_RETURN(0);
}


byte *hash_element(HASH *hash,uint idx)
{
  if (idx < hash->records)
    return dynamic_element(&hash->array,idx,HASH_LINK*)->data;
  return 0;
}


/*
  Replace old row with new row.  This should only be used when key
  isn't changed
*/

void hash_replace(HASH *hash, HASH_SEARCH_STATE *current_record, byte *new_row)
{
  if (*current_record != NO_RECORD)            /* Safety */
    dynamic_element(&hash->array, *current_record, HASH_LINK*)->data= new_row;
}


#ifndef DBUG_OFF

my_bool hash_check(HASH *hash)
{
  int error;
  uint i,rec_link,found,max_links,seek,links,idx;
  uint records,blength;
  HASH_LINK *data,*hash_info;

  records=hash->records; blength=hash->blength;
  data=dynamic_element(&hash->array,0,HASH_LINK*);
  error=0;

  for (i=found=max_links=seek=0 ; i < records ; i++)
  {
    if (hash_rec_mask(hash,data+i,blength,records) == i)
    {
      found++; seek++; links=1;
      for (idx=data[i].next ;
	   idx != NO_RECORD && found < records + 1;
	   idx=hash_info->next)
      {
	if (idx >= records)
	{
	  DBUG_PRINT("error",
		     ("Found pointer outside array to %d from link starting at %d",
		      idx,i));
	  error=1;
	}
	hash_info=data+idx;
	seek+= ++links;
	if ((rec_link=hash_rec_mask(hash,hash_info,blength,records)) != i)
	{
	  DBUG_PRINT("error",
		     ("Record in wrong link at %d: Start %d  Record: 0x%lx  Record-link %d",
                      idx, i, (long) hash_info->data, rec_link));
	  error=1;
	}
	else
	  found++;
      }
      if (links > max_links) max_links=links;
    }
  }
  if (found != records)
  {
    DBUG_PRINT("error",("Found %u of %u records", found, records));
    error=1;
  }
  if (records)
    DBUG_PRINT("info",
	       ("records: %u   seeks: %d   max links: %d   hitrate: %.2f",
		records,seek,max_links,(float) seek / (float) records));
  return error;
}
#endif