_cache.c
上传用户:romrleung
上传日期:2022-05-23
资源大小:18897k
文件大小:3k
- /* Copyright (C) 2000 MySQL AB & MySQL Finland AB & TCX DataKonsult 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 */
- /* Functions for read record cacheing with nisam */
- /* Used instead of my_b_read() to allow for no-cacheed seeks */
- #include "isamdef.h"
- #define READING_NEXT 1
- #define READING_HEADER 2
- /* Copy block from cache if it`s in it. If re_read_if_possibly is */
- /* set read to cache (if after current file-position) else read to */
- /* buff */
- int _nisam_read_cache(IO_CACHE *info, byte *buff, ulong pos, uint length,
- int flag)
- {
- uint read_length,in_buff_length;
- ulong offset;
- char *in_buff_pos;
- if (pos < info->pos_in_file)
- {
- read_length= (uint) min((ulong) length,(ulong) (info->pos_in_file-pos));
- info->seek_not_done=1;
- VOID(my_seek(info->file,pos,MY_SEEK_SET,MYF(0)));
- if (my_read(info->file,buff,read_length,MYF(MY_NABP)))
- return 1;
- if (!(length-=read_length))
- return 0;
- pos+=read_length;
- buff+=read_length;
- }
- if ((offset=pos - (ulong) info->pos_in_file) <
- (ulong) (info->read_end - info->request_pos))
- {
- in_buff_pos=info->request_pos+(uint) offset;
- in_buff_length= min(length,(uint) (info->read_end-in_buff_pos));
- memcpy(buff,info->request_pos+(uint) offset,(size_t) in_buff_length);
- if (!(length-=in_buff_length))
- return 0;
- pos+=in_buff_length;
- buff+=in_buff_length;
- }
- else
- in_buff_length=0;
- if (flag & READING_NEXT)
- {
- if (pos != ((info)->pos_in_file +
- (uint) ((info)->read_end - (info)->request_pos)))
- {
- info->pos_in_file=pos; /* Force start here */
- info->read_pos=info->read_end=info->request_pos; /* Everything used */
- info->seek_not_done=1;
- }
- else
- info->read_pos=info->read_end; /* All block used */
- if (!(*info->read_function)(info,buff,length))
- return 0;
- if (!(flag & READING_HEADER) || info->error == -1 ||
- (uint) info->error+in_buff_length < 3)
- return 1;
- if (BLOCK_INFO_HEADER_LENGTH < in_buff_length + (uint) info->error)
- bzero(buff+info->error,BLOCK_INFO_HEADER_LENGTH - in_buff_length -
- (uint) info->error);
- return 0;
- }
- info->seek_not_done=1;
- VOID(my_seek(info->file,pos,MY_SEEK_SET,MYF(0)));
- if ((read_length=my_read(info->file,buff,length,MYF(0))) == length)
- return 0;
- if (!(flag & READING_HEADER) || (int) read_length == -1 ||
- read_length+in_buff_length < 3)
- return 1;
- bzero(buff+read_length,BLOCK_INFO_HEADER_LENGTH - in_buff_length -
- read_length);
- return 0;
- } /* _nisam_read_cache */