2 * dsf.c: some functions to handle a disjoint set forest,
3 * which is a data structure useful in any solver which has to
4 * worry about avoiding closed loops.
12 /*void print_dsf(int *dsf, int size)
14 int *printed_elements = snewn(size, int);
15 int *equal_elements = snewn(size, int);
16 int *inverse_elements = snewn(size, int);
17 int printed_count = 0, equal_count, inverse_count;
20 memset(printed_elements, -1, sizeof(int) * size);
25 for (i = 0; i < size; ++i) {
26 if (!memchr(printed_elements, i, sizeof(int) * size))
32 i = dsf_canonify(dsf, i);
34 for (n = 0; n < size; ++n) {
35 if (edsf_canonify(dsf, n, &inverse) == i) {
37 inverse_elements[inverse_count++] = n;
39 equal_elements[equal_count++] = n;
43 for (n = 0; n < equal_count; ++n) {
44 fprintf(stderr, "%d ", equal_elements[n]);
45 printed_elements[printed_count++] = equal_elements[n];
48 fprintf(stderr, "!= ");
49 for (n = 0; n < inverse_count; ++n) {
50 fprintf(stderr, "%d ", inverse_elements[n]);
51 printed_elements[printed_count++] = inverse_elements[n];
54 fprintf(stderr, "\n");
58 sfree(printed_elements);
59 sfree(equal_elements);
60 sfree(inverse_elements);
63 void dsf_init(int *dsf
, int size
)
67 for (i
= 0; i
< size
; i
++) {
68 /* Bottom bit of each element of this array stores whether that element
69 * is opposite to its parent, which starts off as false */
74 int *snew_dsf(int size
)
78 ret
= snewn(size
, int);
81 /*print_dsf(ret, size); */
86 int dsf_canonify(int *dsf
, int index
)
88 return edsf_canonify(dsf
, index
, NULL
);
91 void dsf_merge(int *dsf
, int v1
, int v2
)
93 edsf_merge(dsf
, v1
, v2
, FALSE
);
96 int edsf_canonify(int *dsf
, int index
, int *inverse_return
)
98 int start_index
= index
, canonical_index
;
101 /* fprintf(stderr, "dsf = %p\n", dsf); */
102 /* fprintf(stderr, "Canonify %2d\n", index); */
106 /* Find the index of the canonical element of the 'equivalence class' of
107 * which start_index is a member, and figure out whether start_index is the
108 * same as or inverse to that. */
109 while ((dsf
[index
] >> 1) != index
) {
110 inverse
^= (dsf
[index
] & 1);
111 index
= dsf
[index
] >> 1;
112 /* fprintf(stderr, "index = %2d, ", index); */
113 /* fprintf(stderr, "inverse = %d\n", inverse); */
115 canonical_index
= index
;
118 *inverse_return
= inverse
;
120 /* Update every member of this 'equivalence class' to point directly at the
121 * canonical member. */
123 while (index
!= canonical_index
) {
124 int nextindex
= dsf
[index
] >> 1;
125 int nextinverse
= inverse
^ (dsf
[index
] & 1);
126 dsf
[index
] = (canonical_index
<< 1) | inverse
;
127 inverse
= nextinverse
;
131 assert(inverse
== 0);
133 /* fprintf(stderr, "Return %2d\n", index); */
138 void edsf_merge(int *dsf
, int v1
, int v2
, int inverse
)
142 /* fprintf(stderr, "dsf = %p\n", dsf); */
143 /* fprintf(stderr, "Merge [%2d,%2d], %d\n", v1, v2, inverse); */
145 v1
= edsf_canonify(dsf
, v1
, &i1
);
147 v2
= edsf_canonify(dsf
, v2
, &i2
);
150 /* fprintf(stderr, "Doing [%2d,%2d], %d\n", v1, v2, inverse); */
155 dsf
[v2
] = (v1
<< 1) | !!inverse
;
157 v2
= edsf_canonify(dsf
, v2
, &i2
);
159 assert(i2
== inverse
);
161 /* fprintf(stderr, "dsf[%2d] = %2d\n", v2, dsf[v2]); */