/* qsort.c:
*
****************************************************************
* Copyright (C) 1991, 1992, 1996, 1997, 1999 Free Software Foundation, Inc.
* Modifications (C) 2002, Tom Lord
*
* See the file "COPYING" for further information about
* the copyright and warranty status of this work.
*
* This file is snarfed from the GNU C Library and modified for libhackerlab.
* Originally Written by Douglas C. Schmidt (schmidt@ics.uci.edu).
*
*/
#include <limits.h>
#include <stdlib.h>
#include <string.h>
#include "hackerlab/sort/qsort.h"
/* 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)!
*/
/* 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.
*/
struct stack_node
{
char *lo;
char *hi;
};
/* 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 (8 * 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)
/* Byte-wise swap two items of size SIZE.
*/
#define SWAP(a, b, size) \
do \
{ \
size_t __size = (size); \
char * __a; \
char * __b; \
\
__size = (size); \
__a = (a); \
__b = (b); \
\
do \
{ \
char __tmp; \
\
__tmp = *__a; \
*__a++ = *__b; \
*__b++ = __tmp; \
} \
while (--__size > 0); \
} \
while (0)
void
quicksort (void * base,
size_t n_elts,
size_t sizeof_elt,
quicksort_cmp cmp,
void * closure)
{
char * base_ptr;
size_t max_thresh;
if (n_elts == 0)
return;
base_ptr = (char *)base;
max_thresh = MAX_THRESH * sizeof_elt;
if (n_elts > MAX_THRESH)
{
struct stack_node stack[STACK_SIZE];
struct stack_node *top;
char *lo;
char *hi;
top = stack + 1;
lo = base_ptr;
hi = &lo[sizeof_elt * (n_elts - 1)];
while (STACK_NOT_EMPTY)
{
char *left_ptr;
char *right_ptr;
char *mid;
/* 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.
*/
mid = lo + sizeof_elt * ((hi - lo) / sizeof_elt >> 1);
if ((*cmp) ((void *) mid, (void *) lo, closure) < 0)
{
SWAP (mid, lo, sizeof_elt);
}
if ((*cmp) ((void *) hi, (void *) mid, closure) < 0)
{
SWAP (mid, hi, sizeof_elt);
}
else
goto jump_over;
if ((*cmp) ((void *) mid, (void *) lo, closure) < 0)
SWAP (mid, lo, sizeof_elt);
jump_over:
left_ptr = lo + sizeof_elt;
right_ptr = hi - sizeof_elt;
/* 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, closure) < 0)
left_ptr += sizeof_elt;
while ((*cmp) ((void *) mid, (void *) right_ptr, closure) < 0)
right_ptr -= sizeof_elt;
if (left_ptr < right_ptr)
{
SWAP (left_ptr, right_ptr, sizeof_elt);
if (mid == left_ptr)
mid = right_ptr;
else if (mid == right_ptr)
mid = left_ptr;
left_ptr += sizeof_elt;
right_ptr -= sizeof_elt;
}
else if (left_ptr == right_ptr)
{
left_ptr += sizeof_elt;
right_ptr -= sizeof_elt;
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 * end_ptr;
char * tmp_ptr;
char * thresh;
char * run_ptr;
end_ptr = &base_ptr[sizeof_elt * (n_elts - 1)];
tmp_ptr = base_ptr;
thresh = min(end_ptr, base_ptr + max_thresh);
/* 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 + sizeof_elt; run_ptr <= thresh; run_ptr += sizeof_elt)
if ((*cmp) ((void *) run_ptr, (void *) tmp_ptr, closure) < 0)
tmp_ptr = run_ptr;
if (tmp_ptr != base_ptr)
{
SWAP (tmp_ptr, base_ptr, sizeof_elt);
}
/* Insertion sort, running from left-hand-side up to right-hand-side.
*/
run_ptr = base_ptr + sizeof_elt;
while ((run_ptr += sizeof_elt) <= end_ptr)
{
tmp_ptr = run_ptr - sizeof_elt;
while ((*cmp) ((void *) run_ptr, (void *) tmp_ptr, closure) < 0)
tmp_ptr -= sizeof_elt;
tmp_ptr += sizeof_elt;
if (tmp_ptr != run_ptr)
{
char *trav;
trav = run_ptr + sizeof_elt;
while (--trav >= run_ptr)
{
char c;
char * hi;
char * lo;
c = *trav;
for (hi = lo = trav; (lo -= sizeof_elt) >= tmp_ptr; hi = lo)
*hi = *lo;
*hi = c;
}
}
}
}
}
/* tag: Tom Lord Fri Feb 22 06:34:02 2002 (qsort.c)
*/
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