ptr_cmp.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
- 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 */
- /*
- get_ptr_compare(len) returns a pointer to a optimal byte-compare function
- for a array of stringpointer where all strings have size len.
- The bytes are compare as unsigned chars.
- */
- #include "mysys_priv.h"
- static int ptr_compare(uint *compare_length, uchar **a, uchar **b);
- static int ptr_compare_0(uint *compare_length, uchar **a, uchar **b);
- static int ptr_compare_1(uint *compare_length, uchar **a, uchar **b);
- static int ptr_compare_2(uint *compare_length, uchar **a, uchar **b);
- static int ptr_compare_3(uint *compare_length, uchar **a, uchar **b);
- /* Get a pointer to a optimal byte-compare function for a given size */
- qsort2_cmp get_ptr_compare (uint size)
- {
- if (size < 4)
- return (qsort2_cmp) ptr_compare;
- switch (size & 3) {
- case 0: return (qsort2_cmp) ptr_compare_0;
- case 1: return (qsort2_cmp) ptr_compare_1;
- case 2: return (qsort2_cmp) ptr_compare_2;
- case 3: return (qsort2_cmp) ptr_compare_3;
- }
- return 0; /* Impossible */
- }
- /*
- Compare to keys to see witch is smaller.
- Loop unrolled to make it quick !!
- */
- #define cmp(N) if (first[N] != last[N]) return (int) first[N] - (int) last[N]
- static int ptr_compare(uint *compare_length, uchar **a, uchar **b)
- {
- reg3 int length= *compare_length;
- reg1 uchar *first,*last;
- first= *a; last= *b;
- while (--length)
- {
- if (*first++ != *last++)
- return (int) first[-1] - (int) last[-1];
- }
- return (int) first[0] - (int) last[0];
- }
- static int ptr_compare_0(uint *compare_length,uchar **a, uchar **b)
- {
- reg3 int length= *compare_length;
- reg1 uchar *first,*last;
- first= *a; last= *b;
- loop:
- cmp(0);
- cmp(1);
- cmp(2);
- cmp(3);
- if ((length-=4))
- {
- first+=4;
- last+=4;
- goto loop;
- }
- return (0);
- }
- static int ptr_compare_1(uint *compare_length,uchar **a, uchar **b)
- {
- reg3 int length= *compare_length-1;
- reg1 uchar *first,*last;
- first= *a+1; last= *b+1;
- cmp(-1);
- loop:
- cmp(0);
- cmp(1);
- cmp(2);
- cmp(3);
- if ((length-=4))
- {
- first+=4;
- last+=4;
- goto loop;
- }
- return (0);
- }
- static int ptr_compare_2(uint *compare_length,uchar **a, uchar **b)
- {
- reg3 int length= *compare_length-2;
- reg1 uchar *first,*last;
- first= *a +2 ; last= *b +2;
- cmp(-2);
- cmp(-1);
- loop:
- cmp(0);
- cmp(1);
- cmp(2);
- cmp(3);
- if ((length-=4))
- {
- first+=4;
- last+=4;
- goto loop;
- }
- return (0);
- }
- static int ptr_compare_3(uint *compare_length,uchar **a, uchar **b)
- {
- reg3 int length= *compare_length-3;
- reg1 uchar *first,*last;
- first= *a +3 ; last= *b +3;
- cmp(-3);
- cmp(-2);
- cmp(-1);
- loop:
- cmp(0);
- cmp(1);
- cmp(2);
- cmp(3);
- if ((length-=4))
- {
- first+=4;
- last+=4;
- goto loop;
- }
- return (0);
- }