poolalloc/runtime/PreRT/qsort.c - llvm-archive - Git at Google

 /* Copyright (C) 1991,1992,1996,1997,1999,2004 Free Software Foundation, Inc.
    This file is part of the GNU C Library.
    Written by Douglas C. Schmidt (schmidt@ics.uci.edu).

    The GNU C Library is free software; you can redistribute it and/or
    modify it under the terms of the GNU Lesser General Public
    License as published by the Free Software Foundation; either
    version 2.1 of the License, or (at your option) any later version.

    The GNU C Library 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
    Lesser General Public License for more details.

    You should have received a copy of the GNU Lesser General Public
    License along with the GNU C Library; if not, write to the Free
    Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
    02111-1307 USA.  */

 /* If you consider tuning this algorithm, you should consult first:
    Engineering a sort function; Jon Bentley and M. Douglas McIlroy;
    Software - Practice and Experience; Vol. 23 (11), 1249-1265, 1993.  */

 #if defined(__linux__)
 #include <alloca.h>
 #endif
 #include <limits.h>
 #include <stdlib.h>
 #include <string.h>

 /* Byte-wise swap two items of size SIZE. */
 #define SWAP(a, b, size)						      \
   do									      \
     {									      \
       register size_t __size = (size);					      \
       register char *__a = (a), *__b = (b);				      \
       do								      \
 	{								      \
 	  char __tmp = *__a;						      \
 	  *__a++ = *__b;						      \
 	  *__b++ = __tmp;						      \
 	} while (--__size > 0);						      \
     } while (0)

 /* Discontinue quicksort algorithm when partition gets below this size.
    This particular magic number was chosen to work best on a Sun 4/260. */
 #define MAX_THRESH 4

 /* Stack node declarations used to store unfulfilled partition obligations. */
 typedef struct
   {
     char *lo;
     char *hi;
   } stack_node;

 /* The next 4 #defines implement a very fast in-line stack abstraction. */
 /* The stack needs log (total_elements) entries (we could even subtract
    log(MAX_THRESH)).  Since total_elements has type size_t, we get as
    upper bound for log (total_elements):
    bits per byte (CHAR_BIT) * sizeof(size_t).  */
 #define STACK_SIZE	(CHAR_BIT * sizeof(size_t))
 #define PUSH(low, high)	((void) ((top->lo = (low)), (top->hi = (high)), ++top))
 #define	POP(low, high)	((void) (--top, (low = top->lo), (high = top->hi)))
 #define	STACK_NOT_EMPTY	(stack < top)


 /* Order size using quicksort.  This implementation incorporates
    four optimizations discussed in Sedgewick:

    1. Non-recursive, using an explicit stack of pointer that store the
       next array partition to sort.  To save time, this maximum amount
       of space required to store an array of SIZE_MAX is allocated on the
       stack.  Assuming a 32-bit (64 bit) integer for size_t, this needs
       only 32 * sizeof(stack_node) == 256 bytes (for 64 bit: 1024 bytes).
       Pretty cheap, actually.

    2. Chose the pivot element using a median-of-three decision tree.
       This reduces the probability of selecting a bad pivot value and
       eliminates certain extraneous comparisons.

    3. Only quicksorts TOTAL_ELEMS / MAX_THRESH partitions, leaving
       insertion sort to order the MAX_THRESH items within each partition.
       This is a big win, since insertion sort is faster for small, mostly
       sorted array segments.

    4. The larger of the two sub-partitions is always pushed onto the
       stack first, with the algorithm then concentrating on the
       smaller partition.  This *guarantees* no more than log (total_elems)
       stack size is needed (actually O(1) in this case)!  */

 void
 qsort (void *const pbase, size_t total_elems, size_t size,
        int(*cmp)(const void*, const void*))
 {
   register char *base_ptr = (char *) pbase;

   const size_t max_thresh = MAX_THRESH * size;

   if (total_elems == 0)
     /* Avoid lossage with unsigned arithmetic below.  */
     return;

   if (total_elems > MAX_THRESH)
     {
       char *lo = base_ptr;
       char *hi = &lo[size * (total_elems - 1)];
       stack_node stack[STACK_SIZE];
       stack_node *top = stack;

       PUSH (NULL, NULL);

       while (STACK_NOT_EMPTY)
         {
           char *left_ptr;
           char *right_ptr;

 	  /* Select median value from among LO, MID, and HI. Rearrange
 	     LO and HI so the three values are sorted. This lowers the
 	     probability of picking a pathological pivot value and
 	     skips a comparison for both the LEFT_PTR and RIGHT_PTR in
 	     the while loops. */

 	  char *mid = lo + size * ((hi - lo) / size >> 1);

 	  if ((*cmp) ((void *) mid, (void *) lo) < 0)
 	    SWAP (mid, lo, size);
 	  if ((*cmp) ((void *) hi, (void *) mid) < 0)
 	    SWAP (mid, hi, size);
 	  else
 	    goto jump_over;
 	  if ((*cmp) ((void *) mid, (void *) lo) < 0)
 	    SWAP (mid, lo, size);
 	jump_over:;

 	  left_ptr  = lo + size;
 	  right_ptr = hi - size;

 	  /* Here's the famous ``collapse the walls'' section of quicksort.
 	     Gotta like those tight inner loops!  They are the main reason
 	     that this algorithm runs much faster than others. */
 	  do
 	    {
 	      while ((*cmp) ((void *) left_ptr, (void *) mid) < 0)
 		left_ptr += size;

 	      while ((*cmp) ((void *) mid, (void *) right_ptr) < 0)
 		right_ptr -= size;

 	      if (left_ptr < right_ptr)
 		{
 		  SWAP (left_ptr, right_ptr, size);
 		  if (mid == left_ptr)
 		    mid = right_ptr;
 		  else if (mid == right_ptr)
 		    mid = left_ptr;
 		  left_ptr += size;
 		  right_ptr -= size;
 		}
 	      else if (left_ptr == right_ptr)
 		{
 		  left_ptr += size;
 		  right_ptr -= size;
 		  break;
 		}
 	    }
 	  while (left_ptr <= right_ptr);

           /* Set up pointers for next iteration.  First determine whether
              left and right partitions are below the threshold size.  If so,
              ignore one or both.  Otherwise, push the larger partition's
              bounds on the stack and continue sorting the smaller one. */

           if ((size_t) (right_ptr - lo) <= max_thresh)
             {
               if ((size_t) (hi - left_ptr) <= max_thresh)
 		/* Ignore both small partitions. */
                 POP (lo, hi);
               else
 		/* Ignore small left partition. */
                 lo = left_ptr;
             }
           else if ((size_t) (hi - left_ptr) <= max_thresh)
 	    /* Ignore small right partition. */
             hi = right_ptr;
           else if ((right_ptr - lo) > (hi - left_ptr))
             {
 	      /* Push larger left partition indices. */
               PUSH (lo, right_ptr);
               lo = left_ptr;
             }
           else
             {
 	      /* Push larger right partition indices. */
               PUSH (left_ptr, hi);
               hi = right_ptr;
             }
         }
     }

   /* Once the BASE_PTR array is partially sorted by quicksort the rest
      is completely sorted using insertion sort, since this is efficient
      for partitions below MAX_THRESH size. BASE_PTR points to the beginning
      of the array to sort, and END_PTR points at the very last element in
      the array (*not* one beyond it!). */

 #define min(x, y) ((x) < (y) ? (x) : (y))

   {
     char *const end_ptr = &base_ptr[size * (total_elems - 1)];
     char *tmp_ptr = base_ptr;
     char *thresh = min(end_ptr, base_ptr + max_thresh);
     register char *run_ptr;

     /* Find smallest element in first threshold and place it at the
        array's beginning.  This is the smallest array element,
        and the operation speeds up insertion sort's inner loop. */

     for (run_ptr = tmp_ptr + size; run_ptr <= thresh; run_ptr += size)
       if ((*cmp) ((void *) run_ptr, (void *) tmp_ptr) < 0)
         tmp_ptr = run_ptr;

     if (tmp_ptr != base_ptr)
       SWAP (tmp_ptr, base_ptr, size);

     /* Insertion sort, running from left-hand-side up to right-hand-side.  */

     run_ptr = base_ptr + size;
     while ((run_ptr += size) <= end_ptr)
       {
 	tmp_ptr = run_ptr - size;
 	while ((*cmp) ((void *) run_ptr, (void *) tmp_ptr) < 0)
 	  tmp_ptr -= size;

 	tmp_ptr += size;
         if (tmp_ptr != run_ptr)
           {
             char *trav;

 	    trav = run_ptr + size;
 	    while (--trav >= run_ptr)
               {
                 char c = *trav;
                 char *hi, *lo;

                 for (hi = lo = trav; (lo -= size) >= tmp_ptr; hi = lo)
                   *hi = *lo;
                 *hi = c;
               }
           }
       }
   }
 }

 #if 0
 int lt(const void* x, const void* y) {
   int xv = *(int*)x;
   int yv = *(int*)y;
   if (xv < yv) return -1;
   if (xv > yv) return 1;
   return 0;
 }
 int gt(const void* x, const void* y) {
   int xv = *(int*)x;
   int yv = *(int*)y;
   if (xv > yv) return -1;
   if (xv < yv) return 1;
   return 0;
 }

 int main() {
   int size = 100000;
   int* arr = malloc(size*sizeof(int));
   srand(0);
   for (int x = 0; x < size; ++x)
     arr[x] = rand();

   qsort(arr, size, sizeof(int), lt);
   qsort(arr, size, sizeof(int), gt);
   qsort(arr, size, sizeof(int), lt);
   qsort(arr, size, sizeof(int), lt);
   for (int x = 0 ; x < size; ++x)
     printf("%d\n", arr[x]);
   return 0;
 }
 #endif
	/* Copyright (C) 1991,1992,1996,1997,1999,2004 Free Software Foundation, Inc.
	This file is part of the GNU C Library.
	Written by Douglas C. Schmidt (schmidt@ics.uci.edu).

	The GNU C Library is free software; you can redistribute it and/or
	modify it under the terms of the GNU Lesser General Public
	License as published by the Free Software Foundation; either
	version 2.1 of the License, or (at your option) any later version.

	The GNU C Library 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
	Lesser General Public License for more details.

	You should have received a copy of the GNU Lesser General Public
	License along with the GNU C Library; if not, write to the Free
	Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
	02111-1307 USA. */

	/* If you consider tuning this algorithm, you should consult first:
	Engineering a sort function; Jon Bentley and M. Douglas McIlroy;
	Software - Practice and Experience; Vol. 23 (11), 1249-1265, 1993. */

	#if defined(__linux__)
	#include <alloca.h>
	#endif
	#include <limits.h>
	#include <stdlib.h>
	#include <string.h>

	/* Byte-wise swap two items of size SIZE. */
	#define SWAP(a, b, size) \
	do \
	{ \
	register size_t __size = (size); \
	register char __a = (a), __b = (b); \
	do \
	{ \
	char __tmp = *__a; \
	__a++ = __b; \
	*__b++ = __tmp; \
	} while (--__size > 0); \
	} while (0)

	/* Discontinue quicksort algorithm when partition gets below this size.
	This particular magic number was chosen to work best on a Sun 4/260. */
	#define MAX_THRESH 4

	/* Stack node declarations used to store unfulfilled partition obligations. */
	typedef struct
	{
	char *lo;
	char *hi;
	} stack_node;

	/* The next 4 #defines implement a very fast in-line stack abstraction. */
	/* The stack needs log (total_elements) entries (we could even subtract
	log(MAX_THRESH)). Since total_elements has type size_t, we get as
	upper bound for log (total_elements):
	bits per byte (CHAR_BIT) * sizeof(size_t). */
	#define STACK_SIZE (CHAR_BIT * sizeof(size_t))
	#define PUSH(low, high) ((void) ((top->lo = (low)), (top->hi = (high)), ++top))
	#define POP(low, high) ((void) (--top, (low = top->lo), (high = top->hi)))
	#define STACK_NOT_EMPTY (stack < top)


	/* Order size using quicksort. This implementation incorporates
	four optimizations discussed in Sedgewick:

	1. Non-recursive, using an explicit stack of pointer that store the
	next array partition to sort. To save time, this maximum amount
	of space required to store an array of SIZE_MAX is allocated on the
	stack. Assuming a 32-bit (64 bit) integer for size_t, this needs
	only 32 * sizeof(stack_node) == 256 bytes (for 64 bit: 1024 bytes).
	Pretty cheap, actually.

	2. Chose the pivot element using a median-of-three decision tree.
	This reduces the probability of selecting a bad pivot value and
	eliminates certain extraneous comparisons.

	3. Only quicksorts TOTAL_ELEMS / MAX_THRESH partitions, leaving
	insertion sort to order the MAX_THRESH items within each partition.
	This is a big win, since insertion sort is faster for small, mostly
	sorted array segments.

	4. The larger of the two sub-partitions is always pushed onto the
	stack first, with the algorithm then concentrating on the
	smaller partition. This guarantees no more than log (total_elems)
	stack size is needed (actually O(1) in this case)! */

	void
	qsort (void *const pbase, size_t total_elems, size_t size,
	int(cmp)(const void, const void*))
	{
	register char base_ptr = (char ) pbase;

	const size_t max_thresh = MAX_THRESH * size;

	if (total_elems == 0)
	/* Avoid lossage with unsigned arithmetic below. */
	return;

	if (total_elems > MAX_THRESH)
	{
	char *lo = base_ptr;
	char hi = &lo[size (total_elems - 1)];
	stack_node stack[STACK_SIZE];
	stack_node *top = stack;

	PUSH (NULL, NULL);

	while (STACK_NOT_EMPTY)
	{
	char *left_ptr;
	char *right_ptr;

	/* Select median value from among LO, MID, and HI. Rearrange
	LO and HI so the three values are sorted. This lowers the
	probability of picking a pathological pivot value and
	skips a comparison for both the LEFT_PTR and RIGHT_PTR in
	the while loops. */

	char mid = lo + size ((hi - lo) / size >> 1);

	if ((cmp) ((void ) mid, (void *) lo) < 0)
	SWAP (mid, lo, size);
	if ((cmp) ((void ) hi, (void *) mid) < 0)
	SWAP (mid, hi, size);
	else
	goto jump_over;
	if ((cmp) ((void ) mid, (void *) lo) < 0)
	SWAP (mid, lo, size);
	jump_over:;

	left_ptr = lo + size;
	right_ptr = hi - size;

	/* Here's the famous ``collapse the walls'' section of quicksort.
	Gotta like those tight inner loops! They are the main reason
	that this algorithm runs much faster than others. */
	do
	{
	while ((cmp) ((void ) left_ptr, (void *) mid) < 0)
	left_ptr += size;

	while ((cmp) ((void ) mid, (void *) right_ptr) < 0)
	right_ptr -= size;

	if (left_ptr < right_ptr)
	{
	SWAP (left_ptr, right_ptr, size);
	if (mid == left_ptr)
	mid = right_ptr;
	else if (mid == right_ptr)
	mid = left_ptr;
	left_ptr += size;
	right_ptr -= size;
	}
	else if (left_ptr == right_ptr)
	{
	left_ptr += size;
	right_ptr -= size;
	break;
	}
	}
	while (left_ptr <= right_ptr);

	/* Set up pointers for next iteration. First determine whether
	left and right partitions are below the threshold size. If so,
	ignore one or both. Otherwise, push the larger partition's
	bounds on the stack and continue sorting the smaller one. */

	if ((size_t) (right_ptr - lo) <= max_thresh)
	{
	if ((size_t) (hi - left_ptr) <= max_thresh)
	/* Ignore both small partitions. */
	POP (lo, hi);
	else
	/* Ignore small left partition. */
	lo = left_ptr;
	}
	else if ((size_t) (hi - left_ptr) <= max_thresh)
	/* Ignore small right partition. */
	hi = right_ptr;
	else if ((right_ptr - lo) > (hi - left_ptr))
	{
	/* Push larger left partition indices. */
	PUSH (lo, right_ptr);
	lo = left_ptr;
	}
	else
	{
	/* Push larger right partition indices. */
	PUSH (left_ptr, hi);
	hi = right_ptr;
	}
	}
	}

	/* Once the BASE_PTR array is partially sorted by quicksort the rest
	is completely sorted using insertion sort, since this is efficient
	for partitions below MAX_THRESH size. BASE_PTR points to the beginning
	of the array to sort, and END_PTR points at the very last element in
	the array (not one beyond it!). */

	#define min(x, y) ((x) < (y) ? (x) : (y))

	{
	char const end_ptr = &base_ptr[size (total_elems - 1)];
	char *tmp_ptr = base_ptr;
	char *thresh = min(end_ptr, base_ptr + max_thresh);
	register char *run_ptr;

	/* Find smallest element in first threshold and place it at the
	array's beginning. This is the smallest array element,
	and the operation speeds up insertion sort's inner loop. */

	for (run_ptr = tmp_ptr + size; run_ptr <= thresh; run_ptr += size)
	if ((cmp) ((void ) run_ptr, (void *) tmp_ptr) < 0)
	tmp_ptr = run_ptr;

	if (tmp_ptr != base_ptr)
	SWAP (tmp_ptr, base_ptr, size);

	/* Insertion sort, running from left-hand-side up to right-hand-side. */

	run_ptr = base_ptr + size;
	while ((run_ptr += size) <= end_ptr)
	{
	tmp_ptr = run_ptr - size;
	while ((cmp) ((void ) run_ptr, (void *) tmp_ptr) < 0)
	tmp_ptr -= size;

	tmp_ptr += size;
	if (tmp_ptr != run_ptr)
	{
	char *trav;

	trav = run_ptr + size;
	while (--trav >= run_ptr)
	{
	char c = *trav;
	char hi, lo;

	for (hi = lo = trav; (lo -= size) >= tmp_ptr; hi = lo)
	hi = lo;
	*hi = c;
	}
	}
	}
	}
	}

	#if 0
	int lt(const void* x, const void* y) {
	int xv = (int)x;
	int yv = (int)y;
	if (xv < yv) return -1;
	if (xv > yv) return 1;
	return 0;
	}
	int gt(const void* x, const void* y) {
	int xv = (int)x;
	int yv = (int)y;
	if (xv > yv) return -1;
	if (xv < yv) return 1;
	return 0;
	}

	int main() {
	int size = 100000;
	int* arr = malloc(size*sizeof(int));
	srand(0);
	for (int x = 0; x < size; ++x)
	arr[x] = rand();

	qsort(arr, size, sizeof(int), lt);
	qsort(arr, size, sizeof(int), gt);
	qsort(arr, size, sizeof(int), lt);
	qsort(arr, size, sizeof(int), lt);
	for (int x = 0 ; x < size; ++x)
	printf("%d\n", arr[x]);
	return 0;
	}
	#endif