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/* Copyright (C) 1991, 1992, 1996, 1997, 1999 Free Software Foundation, Inc. |
This file is part of the GNU C Library. |
Written by Douglas C. Schmidt (schmidt@ics.uci.edu). |
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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. */ |
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/* 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. */ |
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//#include <alloca.h> //SHARK |
#include <limits.h> |
#include <stdlib.h> |
#include <string.h> |
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/* 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) |
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/* 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 |
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/* Stack node declarations used to store unfulfilled partition obligations. */ |
typedef struct |
{ |
char *lo; |
char *hi; |
} stack_node; |
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/* 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) |
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/* Order size using quicksort. This implementation incorporates |
four optimizations discussed in Sedgewick: |
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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. |
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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. |
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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. |
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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)! */ |
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void |
_quicksort (void *const pbase, size_t total_elems, size_t size, |
__compar_fn_t cmp) |
{ |
register char *base_ptr = (char *) pbase; |
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const size_t max_thresh = MAX_THRESH * size; |
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if (total_elems == 0) |
/* Avoid lossage with unsigned arithmetic below. */ |
return; |
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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 + 1; |
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while (STACK_NOT_EMPTY) |
{ |
char *left_ptr; |
char *right_ptr; |
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/* 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. */ |
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char *mid = lo + size * ((hi - lo) / size >> 1); |
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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:; |
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left_ptr = lo + size; |
right_ptr = hi - size; |
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/* 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; |
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while ((*cmp) ((void *) mid, (void *) right_ptr) < 0) |
right_ptr -= size; |
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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); |
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/* 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. */ |
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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; |
} |
} |
} |
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/* 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!). */ |
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#define min(x, y) ((x) < (y) ? (x) : (y)) |
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{ |
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; |
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/* 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. */ |
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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; |
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if (tmp_ptr != base_ptr) |
SWAP (tmp_ptr, base_ptr, size); |
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/* Insertion sort, running from left-hand-side up to right-hand-side. */ |
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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; |
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tmp_ptr += size; |
if (tmp_ptr != run_ptr) |
{ |
char *trav; |
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trav = run_ptr + size; |
while (--trav >= run_ptr) |
{ |
char c = *trav; |
char *hi, *lo; |
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for (hi = lo = trav; (lo -= size) >= tmp_ptr; hi = lo) |
*hi = *lo; |
*hi = c; |
} |
} |
} |
} |
} |