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/* Copyright (c) 2000, 2015, 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 */
/*
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"
#include <myisampack.h>
/*
* On some platforms, memcmp() is faster than the unrolled ptr_compare_N
* functions, as memcmp() is usually a platform-specific implementation
* written in assembler. for example one in /usr/lib/libc/libc_hwcap*.so.1.
* on Solaris, or on Windows inside C runtime linrary.
*
* On Solaris, native implementation is also usually faster than the
* built-in memcmp supplied by GCC, so it is recommended to build
* with "-fno-builtin-memcmp"in CFLAGS if building with GCC on Solaris.
*/
/*
Daniel Blacks tests shows that libc memcmp is generally faster than
ptr_cmp() at least of x86 and power8 platforms, so we use the libc
code as deafult for now
*/
#define USE_NATIVE_MEMCMP 1
#ifdef USE_NATIVE_MEMCMP
#include <string.h>
static int native_compare(size_t *length, unsigned char **a, unsigned char **b)
{
return memcmp(*a, *b, *length);
}
qsort2_cmp get_ptr_compare (size_t size __attribute__((unused)))
{
return (qsort2_cmp) native_compare;
}
#else /* USE_NATIVE_MEMCMP */
static int ptr_compare(size_t *compare_length, uchar **a, uchar **b);
static int ptr_compare_0(size_t *compare_length, uchar **a, uchar **b);
static int ptr_compare_1(size_t *compare_length, uchar **a, uchar **b);
static int ptr_compare_2(size_t *compare_length, uchar **a, uchar **b);
static int ptr_compare_3(size_t *compare_length, uchar **a, uchar **b);
static int degenerate_compare_func(size_t *compare_length, uchar **a, uchar **b)
{
DBUG_ASSERT(*compare_length == 0);
return 0;
}
qsort2_cmp get_ptr_compare (size_t size)
{
if (size == 0)
return (qsort2_cmp) degenerate_compare_func;
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(size_t *compare_length, uchar **a, uchar **b)
{
size_t length= *compare_length;
uchar *first,*last;
DBUG_ASSERT(length > 0);
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(size_t *compare_length,uchar **a, uchar **b)
{
size_t length= *compare_length;
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(size_t *compare_length,uchar **a, uchar **b)
{
size_t length= *compare_length-1;
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(size_t *compare_length,uchar **a, uchar **b)
{
size_t length= *compare_length-2;
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(size_t *compare_length,uchar **a, uchar **b)
{
size_t length= *compare_length-3;
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);
}
#endif /* USE_NATIVE_MEMCMP */
void my_store_ptr(uchar *buff, size_t pack_length, my_off_t pos)
{
switch (pack_length) {
#if SIZEOF_OFF_T > 4
case 8: mi_int8store(buff,pos); break;
case 7: mi_int7store(buff,pos); break;
case 6: mi_int6store(buff,pos); break;
case 5: mi_int5store(buff,pos); break;
#endif
case 4: mi_int4store(buff,pos); break;
case 3: mi_int3store(buff,pos); break;
case 2: mi_int2store(buff,pos); break;
case 1: buff[0]= (uchar) pos; break;
default: DBUG_ASSERT(0);
}
return;
}
my_off_t my_get_ptr(uchar *ptr, size_t pack_length)
{
my_off_t pos;
switch (pack_length) {
#if SIZEOF_OFF_T > 4
case 8: pos= (my_off_t) mi_uint8korr(ptr); break;
case 7: pos= (my_off_t) mi_uint7korr(ptr); break;
case 6: pos= (my_off_t) mi_uint6korr(ptr); break;
case 5: pos= (my_off_t) mi_uint5korr(ptr); break;
#endif
case 4: pos= (my_off_t) mi_uint4korr(ptr); break;
case 3: pos= (my_off_t) mi_uint3korr(ptr); break;
case 2: pos= (my_off_t) mi_uint2korr(ptr); break;
case 1: pos= (my_off_t) *(uchar*) ptr; break;
default: DBUG_ASSERT(0); return 0;
}
return pos;
}
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