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
|
/******************************************************************/
/* qsort.c -- Non-Recursive ANSI Quicksort function */
/* */
/* Public domain by Raymond Gardner, Englewood CO February 1991 */
/* */
/* Usage: */
/* qsort(base, nbr_elements, width_bytes, compare_function); */
/* void *base; */
/* size_t nbr_elements, width_bytes; */
/* int (*compare_function)(const void *, const void *); */
/* */
/* Sorts an array starting at base, of length nbr_elements, each */
/* element of size width_bytes, ordered via compare_function, */
/* which is called as (*compare_function)(ptr_to_element1, */
/* ptr_to_element2) and returns < 0 if element1 < element2, */
/* 0 if element1 = element2, > 0 if element1 > element2. */
/* Most refinements are due to R. Sedgewick. See "Implementing */
/* Quicksort Programs", Comm. ACM, Oct. 1978, and Corrigendum, */
/* Comm. ACM, June 1979. */
/******************************************************************/
#include <stddef.h> /* for size_t definition */
/* prototypes */
void qsort(void *, size_t, size_t,
int (*)(const void *, const void *));
void swap_chars(char *, char *, size_t);
/*
** Compile with -DSWAP_INTS if your machine can access an int at an
** arbitrary location with reasonable efficiency. (Some machines
** cannot access an int at an odd address at all, so be careful.)
*/
#ifdef SWAP_INTS
void swap_ints(char *, char *, size_t);
#define SWAP(a, b) (swap_func((char *)(a), (char *)(b), width))
#else
#define SWAP(a, b) (swap_chars((char *)(a), (char *)(b), size))
#endif
#define COMP(a, b) ((*comp)((void *)(a), (void *)(b)))
#define T 7 /* subfiles of T or fewer elements will */
/* be sorted by a simple insertion sort */
/* Note! T must be at least 3 */
void qsort(void *basep, size_t nelems, size_t size,
int (*comp)(const void *, const void *))
{
char *stack[40], **sp; /* stack and stack pointer */
char *i, *j, *limit; /* scan and limit pointers */
size_t thresh; /* size of T elements in bytes */
char *base; /* base pointer as char * */
#ifdef SWAP_INTS
size_t width; /* width of array element */
void (*swap_func)(char *, char *, size_t); /* swap func pointer*/
width = size; /* save size for swap routine */
swap_func = swap_chars; /* choose swap function */
if ( size % sizeof(int) == 0 ) { /* size is multiple of ints */
width /= sizeof(int); /* set width in ints */
swap_func = swap_ints; /* use int swap function */
}
#endif
base = (char *)basep; /* set up char * base pointer */
thresh = T * size; /* init threshold */
sp = stack; /* init stack pointer */
limit = base + nelems * size;/* pointer past end of array */
for ( ;; ) { /* repeat until break... */
if ( limit - base > thresh ) { /* if more than T elements */
/* swap base with middle */
SWAP((((limit-base)/size)/2)*size+base, base);
i = base + size; /* i scans left to right */
j = limit - size; /* j scans right to left */
if ( COMP(i, j) > 0 ) /* Sedgewick's */
SWAP(i, j); /* three-element sort */
if ( COMP(base, j) > 0 ) /* sets things up */
SWAP(base, j); /* so that */
if ( COMP(i, base) > 0 ) /* *i <= *base <= *j */
SWAP(i, base); /* *base is pivot element */
for ( ;; ) { /* loop until break */
do /* move i right */
i += size; /* until *i >= pivot */
while ( COMP(i, base) < 0 );
do /* move j left */
j -= size; /* until *j <= pivot */
while ( COMP(j, base) > 0 );
if ( i > j ) /* if pointers crossed */
break; /* break loop */
SWAP(i, j); /* else swap elements, keep scanning*/
}
SWAP(base, j); /* move pivot into correct place */
if ( j - base > limit - i ) { /* if left subfile larger */
sp[0] = base; /* stack left subfile base */
sp[1] = j; /* and limit */
base = i; /* sort the right subfile */
} else { /* else right subfile larger*/
sp[0] = i; /* stack right subfile base */
sp[1] = limit; /* and limit */
limit = j; /* sort the left subfile */
}
sp += 2; /* increment stack pointer */
} else { /* else subfile is small, use insertion sort */
for ( j = base, i = j+size; i < limit; j = i, i += size )
for ( ; COMP(j, j+size) > 0; j -= size ) {
SWAP(j, j+size);
if ( j == base )
break;
}
if ( sp != stack ) { /* if any entries on stack */
sp -= 2; /* pop the base and limit */
base = sp[0];
limit = sp[1];
} else /* else stack empty, done */
break;
}
}
}
/*
** swap nbytes between a and b
*/
static void swap_chars(char *a, char *b, size_t nbytes)
{
char tmp;
do {
tmp = *a; *a++ = *b; *b++ = tmp;
} while ( --nbytes );
}
#ifdef SWAP_INTS
/*
** swap nints between a and b
*/
static void swap_ints(char *ap, char *bp, size_t nints)
{
int *a = (int *)ap, *b = (int *)bp;
int tmp;
do {
tmp = *a; *a++ = *b; *b++ = tmp;
} while ( --nints );
}
#endif
|
