text: /*
     Copyright (c) 2000, 2010, Oracle and/or its affiliates. All rights reserved.
  
     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; version 2 of the License.
  
     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., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301  USA
  */
  
  
  /**
    @file
  
    @brief
    Buffers to save and compare item values
  */
  
  #include "mysql_priv.h"
  
  /**
    Create right type of Cached_item for an item.
  */
  
  Cached_item *new_Cached_item(THD *thd, Item *item)
  {
    if (item->real_item()->type() == Item::FIELD_ITEM &&
        !(((Item_field *) (item->real_item()))->field->flags & BLOB_FLAG))
      return new Cached_item_field((Item_field *) (item->real_item()));
    switch (item->result_type()) {
    case STRING_RESULT:
      return new Cached_item_str(thd, (Item_field *) item);
    case INT_RESULT:
      return new Cached_item_int((Item_field *) item);
    case REAL_RESULT:
      return new Cached_item_real(item);
    case DECIMAL_RESULT:
      return new Cached_item_decimal(item);
    case ROW_RESULT:
    default:
      DBUG_ASSERT(0);
      return 0;
    }
  }
  
  Cached_item::~Cached_item() {}
  
  /**
    Compare with old value and replace value with new value.
  
    @return
      Return true if values have changed
  */
  
  Cached_item_str::Cached_item_str(THD *thd, Item *arg)
    :item(arg),
     value_max_length(min(arg->max_length, thd->variables.max_sort_length)),
     value(value_max_length)
  {}
  
  bool Cached_item_str::cmp(void)
  {
    String *res;
    bool tmp;
  
    if ((res=item->val_str(&tmp_value)))
      res->length(min(res->length(), value_max_length));
    if (null_value != item->null_value)
    {
      if ((null_value= item->null_value))
        return TRUE;				// New value was null
      tmp=TRUE;
    }
    else if (null_value)
      return 0;					// new and old value was null
    else
      tmp= sortcmp(&value,res,item->collation.collation) != 0;
    if (tmp)
      value.copy(*res);				// Remember for next cmp
    return tmp;
  }
  
  Cached_item_str::~Cached_item_str()
  {
    item=0;					// Safety
  }
  
  bool Cached_item_real::cmp(void)
  {
    double nr= item->val_real();
    if (null_value != item->null_value || nr != value)
    {
      null_value= item->null_value;
      value=nr;
      return TRUE;
    }
    return FALSE;
  }
  
  bool Cached_item_int::cmp(void)
  {
    longlong nr=item->val_int();
    if (null_value != item->null_value || nr != value)
    {
      null_value= item->null_value;
      value=nr;
      return TRUE;
    }
    return FALSE;
  }
  
  
  bool Cached_item_field::cmp(void)
  {
    bool tmp= field->cmp(buff) != 0;		// This is not a blob!
    if (tmp)
      field->get_image(buff,length,field->charset());
    if (null_value != field->is_null())
    {
      null_value= !null_value;
      tmp=TRUE;
    }
    return tmp;
  }
  
  
  Cached_item_decimal::Cached_item_decimal(Item *it)
    :item(it)
  {
    my_decimal_set_zero(&value);
  }
  
  
  bool Cached_item_decimal::cmp()
  {
    my_decimal tmp;
    my_decimal *ptmp= item->val_decimal(&tmp);
    if (null_value != item->null_value ||
        (!item->null_value && my_decimal_cmp(&value, ptmp)))
    {
      null_value= item->null_value;
      /* Save only not null values */
      if (!null_value)
      {
        my_decimal2decimal(ptmp, &value);
        return TRUE;
      }
      return FALSE;
    }
    return FALSE;
  }
  
  
  /*****************************************************************************
  ** Instansiate templates
  *****************************************************************************/
  
  #ifdef HAVE_EXPLICIT_TEMPLATE_INSTANTIATION
  template class List<Cached_item>;
  template class List_iterator<Cached_item>;
  #endif
  