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/* 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; 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., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA */
/*
qsort implementation optimized for comparison of pointers
Inspired by the qsort implementations by Douglas C. Schmidt,
and Bentley & McIlroy's "Engineering a Sort Function".
*/
#include "mysys_priv.h"
#include <mystrings/m_string.h>
/* We need to use qsort with 2 different compare functions */
#ifdef QSORT_EXTRA_CMP_ARGUMENT
#define CMP(A,B) ((*cmp)(cmp_argument,(A),(B)))
#else
#define CMP(A,B) ((*cmp)((A),(B)))
#endif
#define SWAP(A, B, size,swap_ptrs) \
do { \
if (swap_ptrs) \
{ \
register char **a = (char**) (A), **b = (char**) (B); \
char *tmp = *a; *a++ = *b; *b++ = tmp; \
} \
else \
{ \
register char *a = (A), *b = (B); \
register char *end= a+size; \
do \
{ \
char tmp = *a; *a++ = *b; *b++ = tmp; \
} while (a < end); \
} \
} while (0)
/* Put the median in the middle argument */
#define MEDIAN(low, mid, high) \
{ \
if (CMP(high,low) < 0) \
SWAP(high, low, size, ptr_cmp); \
if (CMP(mid, low) < 0) \
SWAP(mid, low, size, ptr_cmp); \
else if (CMP(high, mid) < 0) \
SWAP(mid, high, size, ptr_cmp); \
}
/* The following node is used to store ranges to avoid recursive calls */
typedef struct st_stack
{
char *low,*high;
} stack_node;
#define PUSH(LOW,HIGH) {stack_ptr->low = LOW; stack_ptr++->high = HIGH;}
#define POP(LOW,HIGH) {LOW = (--stack_ptr)->low; HIGH = stack_ptr->high;}
/* The following stack size is enough for ulong ~0 elements */
#define STACK_SIZE (8 * sizeof(unsigned long int))
#define THRESHOLD_FOR_INSERT_SORT 10
#if defined(QSORT_TYPE_IS_VOID)
#define SORT_RETURN return
#else
#define SORT_RETURN return 0
#endif
/****************************************************************************
** 'standard' quicksort with the following extensions:
**
** Can be compiled with the qsort2_cmp compare function
** Store ranges on stack to avoid recursion
** Use insert sort on small ranges
** Optimize for sorting of pointers (used often by MySQL)
** Use median comparison to find partition element
*****************************************************************************/
#ifdef QSORT_EXTRA_CMP_ARGUMENT
qsort_t my_qsort2(void *base_ptr, size_t count, size_t size, qsort2_cmp cmp,
void *cmp_argument)
#else
qsort_t my_qsort(void *base_ptr, size_t count, size_t size, qsort_cmp cmp)
#endif
{
char *low, *high, *pivot;
stack_node stack[STACK_SIZE], *stack_ptr;
bool ptr_cmp;
/* Handle the simple case first */
/* This will also make the rest of the code simpler */
if (count <= 1)
SORT_RETURN;
low = (char*) base_ptr;
high = low+ size * (count - 1);
stack_ptr = stack + 1;
#ifdef HAVE_purify
/* The first element in the stack will be accessed for the last POP */
stack[0].low=stack[0].high=0;
#endif
pivot = (char *) my_alloca((int) size);
ptr_cmp= size == sizeof(char*) && !((low - (char*) 0)& (sizeof(char*)-1));
/* The following loop sorts elements between high and low */
do
{
char *low_ptr, *high_ptr, *mid;
count=((size_t) (high - low) / size)+1;
/* If count is small, then an insert sort is faster than qsort */
if (count < THRESHOLD_FOR_INSERT_SORT)
{
for (low_ptr = low + size; low_ptr <= high; low_ptr += size)
{
char *ptr;
for (ptr = low_ptr; ptr > low && CMP(ptr - size, ptr) > 0;
ptr -= size)
SWAP(ptr, ptr - size, size, ptr_cmp);
}
POP(low, high);
continue;
}
/* Try to find a good middle element */
mid= low + size * (count >> 1);
if (count > 40) /* Must be bigger than 24 */
{
size_t step = size* (count / 8);
MEDIAN(low, low + step, low+step*2);
MEDIAN(mid - step, mid, mid+step);
MEDIAN(high - 2 * step, high-step, high);
/* Put best median in 'mid' */
MEDIAN(low+step, mid, high-step);
low_ptr = low;
high_ptr = high;
}
else
{
MEDIAN(low, mid, high);
/* The low and high argument are already in sorted against 'pivot' */
low_ptr = low + size;
high_ptr = high - size;
}
memcpy(pivot, mid, size);
do
{
while (CMP(low_ptr, pivot) < 0)
low_ptr += size;
while (CMP(pivot, high_ptr) < 0)
high_ptr -= size;
if (low_ptr < high_ptr)
{
SWAP(low_ptr, high_ptr, size, ptr_cmp);
low_ptr += size;
high_ptr -= size;
}
else
{
if (low_ptr == high_ptr)
{
low_ptr += size;
high_ptr -= size;
}
break;
}
}
while (low_ptr <= high_ptr);
/*
Prepare for next iteration.
Skip partitions of size 1 as these doesn't have to be sorted
Push the larger partition and sort the smaller one first.
This ensures that the stack is keept small.
*/
if ((int) (high_ptr - low) <= 0)
{
if ((int) (high - low_ptr) <= 0)
{
POP(low, high); /* Nothing more to sort */
}
else
low = low_ptr; /* Ignore small left part. */
}
else if ((int) (high - low_ptr) <= 0)
high = high_ptr; /* Ignore small right part. */
else if ((high_ptr - low) > (high - low_ptr))
{
PUSH(low, high_ptr); /* Push larger left part */
low = low_ptr;
}
else
{
PUSH(low_ptr, high); /* Push larger right part */
high = high_ptr;
}
} while (stack_ptr > stack);
my_afree(pivot);
SORT_RETURN;
}
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