/* Copyright (c) 2000, 2021, Oracle and/or its affiliates.

   This program is free software; you can redistribute it and/or modify
   it under the terms of the GNU General Public License, version 2.0,
   as published by the Free Software Foundation.

   This program is also distributed with certain software (including
   but not limited to OpenSSL) that is licensed under separate terms,
   as designated in a particular file or component or in included license
   documentation.  The authors of MySQL hereby grant you an additional
   permission to link the program and your derivative works with the
   separately licensed software that they have included with MySQL.

   Without limiting anything contained in the foregoing, this file,
   which is part of C Driver for MySQL (Connector/C), is also subject to the
   Universal FOSS Exception, version 1.0, a copy of which can be found at
   http://oss.oracle.com/licenses/universal-foss-exception.

   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, version 2.0, 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 */

/*
  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 "my_sys.h"
#include <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)					\
   {							\
     char **a = (char**) (A), **b = (char**) (B);  \
     char *tmp = *a; *a++ = *b; *b++ = tmp;		\
   }							\
   else							\
   {							\
     char *a = (A), *b = (B);			\
     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

/****************************************************************************
** '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
void my_qsort2(void *base_ptr, size_t count, size_t size, qsort2_cmp cmp,
               const void *cmp_argument)
#else
void 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;
  my_bool ptr_cmp;
  /* Handle the simple case first */
  /* This will also make the rest of the code simpler */
  if (count <= 1)
    return;

  low  = (char*) base_ptr;
  high = low+ size * (count - 1);
  stack_ptr = stack + 1;
  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);
  return;
}
