1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
|
/* qsort( void *, size_t, size_t, int(*)( const void *, const void * ) )
This file is part of the Public Domain C Library (PDCLib).
Permission is granted to use, modify, and / or redistribute at will.
*/
#include <stdlib.h>
#ifndef REGTEST
/* This implementation is taken from Paul Edward's PDPCLIB.
Original code is credited to Raymond Gardner, Englewood CO.
Minor mods are credited to Paul Edwards.
Some reformatting and simplification done by Martin Baute.
All code is still Public Domain.
*/
/* Wrapper for _PDCLIB_memswp protects against multiple argument evaluation. */
static _PDCLIB_inline void memswp( char * i, char * j, size_t size )
{
_PDCLIB_memswp( i, j, size );
}
/* For small sets, insertion sort is faster than quicksort.
T is the threshold below which insertion sort will be used.
Must be 3 or larger.
*/
#define T 7
/* Macros for handling the QSort stack */
#define PREPARE_STACK char * stack[STACKSIZE]; char * * stackptr = stack
#define PUSH( base, limit ) stackptr[0] = base; stackptr[1] = limit; stackptr += 2
#define POP( base, limit ) stackptr -= 2; base = stackptr[0]; limit = stackptr[1]
/* TODO: Stack usage is log2( nmemb ) (minus what T shaves off the worst case).
Worst-case nmemb is platform dependent and should probably be
configured through _PDCLIB_config.h.
*/
#define STACKSIZE 64
void qsort( void * base, size_t nmemb, size_t size, int (*compar)( const void *, const void * ) )
{
char * i;
char * j;
_PDCLIB_size_t thresh = T * size;
char * base_ = (char *)base;
char * limit = base_ + nmemb * size;
PREPARE_STACK;
for ( ;; )
{
if ( (size_t)( limit - base_ ) > thresh ) /* QSort for more than T elements. */
{
/* We work from second to last - first will be pivot element. */
i = base_ + size;
j = limit - size;
/* We swap first with middle element, then sort that with second
and last element so that eventually first element is the median
of the three - avoiding pathological pivots.
TODO: Instead of middle element, chose one randomly.
*/
memswp( ( ( ( (size_t)( limit - base_ ) ) / size ) / 2 ) * size + base_, base_, size );
if ( compar( i, j ) > 0 ) memswp( i, j, size );
if ( compar( base_, j ) > 0 ) memswp( base_, j, size );
if ( compar( i, base_ ) > 0 ) memswp( i, base_, size );
/* Now we have the median for pivot element, entering main Quicksort. */
for ( ;; )
{
do
{
/* move i right until *i >= pivot */
i += size;
} while ( compar( i, base_ ) < 0 );
do
{
/* move j left until *j <= pivot */
j -= size;
} while ( compar( j, base_ ) > 0 );
if ( i > j )
{
/* break loop if pointers crossed */
break;
}
/* else swap elements, keep scanning */
memswp( i, j, size );
}
/* move pivot into correct place */
memswp( base_, j, size );
/* larger subfile base / limit to stack, sort smaller */
if ( j - base_ > limit - i )
{
/* left is larger */
PUSH( base_, j );
base_ = i;
}
else
{
/* right is larger */
PUSH( i, limit );
limit = j;
}
}
else /* insertion sort for less than T elements */
{
for ( j = base_, i = j + size; i < limit; j = i, i += size )
{
for ( ; compar( j, j + size ) > 0; j -= size )
{
memswp( j, j + size, size );
if ( j == base_ )
{
break;
}
}
}
if ( stackptr != stack ) /* if any entries on stack */
{
POP( base_, limit );
}
else /* else stack empty, done */
{
break;
}
}
}
}
#endif
#ifdef TEST
#include "_PDCLIB_test.h"
#include <string.h>
#include <limits.h>
static int compare( const void * left, const void * right )
{
return *( (unsigned char *)left ) - *( (unsigned char *)right );
}
int main( void )
{
char presort[] = { "shreicnyjqpvozxmbt" };
char sorted1[] = { "bcehijmnopqrstvxyz" };
char sorted2[] = { "bticjqnyozpvreshxm" };
char s[19];
strcpy( s, presort );
qsort( s, 18, 1, compare );
TESTCASE( strcmp( s, sorted1 ) == 0 );
strcpy( s, presort );
qsort( s, 9, 2, compare );
TESTCASE( strcmp( s, sorted2 ) == 0 );
strcpy( s, presort );
qsort( s, 1, 1, compare );
TESTCASE( strcmp( s, presort ) == 0 );
#if defined( REGTEST ) && ( defined( __BSD_VISIBLE ) || defined( __APPLE__ ) )
puts( "qsort.c: Skipping test #4 for BSD as it goes into endless loop here." );
#else
qsort( s, 100, 0, compare );
TESTCASE( strcmp( s, presort ) == 0 );
#endif
return TEST_RESULTS;
}
#endif
|
