aboutsummaryrefslogtreecommitdiff
path: root/src/common/container.c
blob: c741eb02065afe0fb9b70fa99b2761e8072ef883 (plain)
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
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
1090
1091
1092
1093
1094
1095
1096
1097
1098
1099
1100
1101
1102
1103
1104
1105
1106
1107
1108
1109
1110
1111
1112
1113
1114
1115
1116
1117
1118
1119
1120
1121
1122
1123
1124
1125
1126
1127
1128
1129
1130
1131
1132
1133
1134
1135
1136
1137
1138
1139
1140
1141
1142
1143
1144
1145
1146
1147
1148
1149
1150
1151
1152
1153
1154
1155
1156
1157
1158
1159
1160
1161
1162
1163
1164
1165
1166
1167
1168
1169
1170
1171
1172
1173
1174
1175
1176
1177
1178
1179
1180
1181
1182
1183
1184
1185
1186
1187
1188
1189
1190
1191
1192
1193
1194
1195
1196
1197
1198
1199
1200
1201
1202
1203
1204
1205
1206
1207
1208
1209
1210
1211
1212
1213
1214
1215
1216
1217
1218
1219
1220
1221
1222
1223
1224
1225
1226
1227
1228
1229
1230
1231
1232
1233
1234
1235
1236
1237
1238
1239
1240
1241
1242
1243
1244
1245
1246
1247
1248
1249
1250
1251
1252
1253
1254
/* Copyright (c) 2003-2004, Roger Dingledine
 * Copyright (c) 2004-2006, Roger Dingledine, Nick Mathewson.
 * Copyright (c) 2007-2011, The Tor Project, Inc. */
/* See LICENSE for licensing information */

/**
 * \file container.c
 * \brief Implements a smartlist (a resizable array) along
 * with helper functions to use smartlists.  Also includes
 * hash table implementations of a string-to-void* map, and of
 * a digest-to-void* map.
 **/

#include "compat.h"
#include "util.h"
#include "log.h"
#include "container.h"
#include "crypto.h"

#include <stdlib.h>
#include <string.h>
#include <assert.h>

#include "ht.h"

/** All newly allocated smartlists have this capacity. */
#define SMARTLIST_DEFAULT_CAPACITY 16

/** Allocate and return an empty smartlist.
 */
smartlist_t *
smartlist_create(void)
{
  smartlist_t *sl = tor_malloc(sizeof(smartlist_t));
  sl->num_used = 0;
  sl->capacity = SMARTLIST_DEFAULT_CAPACITY;
  sl->list = tor_malloc(sizeof(void *) * sl->capacity);
  return sl;
}

/** Deallocate a smartlist.  Does not release storage associated with the
 * list's elements.
 */
void
smartlist_free(smartlist_t *sl)
{
  tor_assert(sl != NULL);
  tor_free(sl->list);
  tor_free(sl);
}

/** Remove all elements from the list.
 */
void
smartlist_clear(smartlist_t *sl)
{
  sl->num_used = 0;
}

/** Make sure that <b>sl</b> can hold at least <b>size</b> entries. */
static INLINE void
smartlist_ensure_capacity(smartlist_t *sl, int size)
{
  if (size > sl->capacity) {
    int higher = sl->capacity * 2;
    while (size > higher)
      higher *= 2;
    tor_assert(higher > 0); /* detect overflow */
    sl->capacity = higher;
    sl->list = tor_realloc(sl->list, sizeof(void*)*sl->capacity);
  }
}

/** Append element to the end of the list. */
void
smartlist_add(smartlist_t *sl, void *element)
{
  smartlist_ensure_capacity(sl, sl->num_used+1);
  sl->list[sl->num_used++] = element;
}

/** Append each element from S2 to the end of S1. */
void
smartlist_add_all(smartlist_t *s1, const smartlist_t *s2)
{
  int new_size = s1->num_used + s2->num_used;
  tor_assert(new_size >= s1->num_used); /* check for overflow. */
  smartlist_ensure_capacity(s1, new_size);
  memcpy(s1->list + s1->num_used, s2->list, s2->num_used*sizeof(void*));
  s1->num_used = new_size;
}

/** Remove all elements E from sl such that E==element.  Preserve
 * the order of any elements before E, but elements after E can be
 * rearranged.
 */
void
smartlist_remove(smartlist_t *sl, const void *element)
{
  int i;
  if (element == NULL)
    return;
  for (i=0; i < sl->num_used; i++)
    if (sl->list[i] == element) {
      sl->list[i] = sl->list[--sl->num_used]; /* swap with the end */
      i--; /* so we process the new i'th element */
    }
}

/** If <b>sl</b> is nonempty, remove and return the final element.  Otherwise,
 * return NULL. */
void *
smartlist_pop_last(smartlist_t *sl)
{
  tor_assert(sl);
  if (sl->num_used)
    return sl->list[--sl->num_used];
  else
    return NULL;
}

/** Reverse the order of the items in <b>sl</b>. */
void
smartlist_reverse(smartlist_t *sl)
{
  int i, j;
  void *tmp;
  tor_assert(sl);
  for (i = 0, j = sl->num_used-1; i < j; ++i, --j) {
    tmp = sl->list[i];
    sl->list[i] = sl->list[j];
    sl->list[j] = tmp;
  }
}

/** If there are any strings in sl equal to element, remove and free them.
 * Does not preserve order. */
void
smartlist_string_remove(smartlist_t *sl, const char *element)
{
  int i;
  tor_assert(sl);
  tor_assert(element);
  for (i = 0; i < sl->num_used; ++i) {
    if (!strcmp(element, sl->list[i])) {
      tor_free(sl->list[i]);
      sl->list[i] = sl->list[--sl->num_used]; /* swap with the end */
      i--; /* so we process the new i'th element */
    }
  }
}

/** Return true iff some element E of sl has E==element.
 */
int
smartlist_isin(const smartlist_t *sl, const void *element)
{
  int i;
  for (i=0; i < sl->num_used; i++)
    if (sl->list[i] == element)
      return 1;
  return 0;
}

/** Return true iff <b>sl</b> has some element E such that
 * !strcmp(E,<b>element</b>)
 */
int
smartlist_string_isin(const smartlist_t *sl, const char *element)
{
  int i;
  if (!sl) return 0;
  for (i=0; i < sl->num_used; i++)
    if (strcmp((const char*)sl->list[i],element)==0)
      return 1;
  return 0;
}

/** If <b>element</b> is equal to an element of <b>sl</b>, return that
 * element's index.  Otherwise, return -1. */
int
smartlist_string_pos(const smartlist_t *sl, const char *element)
{
  int i;
  if (!sl) return -1;
  for (i=0; i < sl->num_used; i++)
    if (strcmp((const char*)sl->list[i],element)==0)
      return i;
  return -1;
}

/** Return true iff <b>sl</b> has some element E such that
 * !strcasecmp(E,<b>element</b>)
 */
int
smartlist_string_isin_case(const smartlist_t *sl, const char *element)
{
  int i;
  if (!sl) return 0;
  for (i=0; i < sl->num_used; i++)
    if (strcasecmp((const char*)sl->list[i],element)==0)
      return 1;
  return 0;
}

/** Return true iff <b>sl</b> has some element E such that E is equal
 * to the decimal encoding of <b>num</b>.
 */
int
smartlist_string_num_isin(const smartlist_t *sl, int num)
{
  char buf[16];
  tor_snprintf(buf,sizeof(buf),"%d", num);
  return smartlist_string_isin(sl, buf);
}

/** Return true iff <b>sl</b> has some element E such that
 * tor_memeq(E,<b>element</b>,DIGEST_LEN)
 */
int
smartlist_digest_isin(const smartlist_t *sl, const char *element)
{
  int i;
  if (!sl) return 0;
  for (i=0; i < sl->num_used; i++)
    if (tor_memeq((const char*)sl->list[i],element,DIGEST_LEN))
      return 1;
  return 0;
}

/** Return true iff some element E of sl2 has smartlist_isin(sl1,E).
 */
int
smartlist_overlap(const smartlist_t *sl1, const smartlist_t *sl2)
{
  int i;
  for (i=0; i < sl2->num_used; i++)
    if (smartlist_isin(sl1, sl2->list[i]))
      return 1;
  return 0;
}

/** Remove every element E of sl1 such that !smartlist_isin(sl2,E).
 * Does not preserve the order of sl1.
 */
void
smartlist_intersect(smartlist_t *sl1, const smartlist_t *sl2)
{
  int i;
  for (i=0; i < sl1->num_used; i++)
    if (!smartlist_isin(sl2, sl1->list[i])) {
      sl1->list[i] = sl1->list[--sl1->num_used]; /* swap with the end */
      i--; /* so we process the new i'th element */
    }
}

/** Remove every element E of sl1 such that smartlist_isin(sl2,E).
 * Does not preserve the order of sl1.
 */
void
smartlist_subtract(smartlist_t *sl1, const smartlist_t *sl2)
{
  int i;
  for (i=0; i < sl2->num_used; i++)
    smartlist_remove(sl1, sl2->list[i]);
}

/** Remove the <b>idx</b>th element of sl; if idx is not the last
 * element, swap the last element of sl into the <b>idx</b>th space.
 * Return the old value of the <b>idx</b>th element.
 */
void
smartlist_del(smartlist_t *sl, int idx)
{
  tor_assert(sl);
  tor_assert(idx>=0);
  tor_assert(idx < sl->num_used);
  sl->list[idx] = sl->list[--sl->num_used];
}

/** Remove the <b>idx</b>th element of sl; if idx is not the last element,
 * moving all subsequent elements back one space. Return the old value
 * of the <b>idx</b>th element.
 */
void
smartlist_del_keeporder(smartlist_t *sl, int idx)
{
  tor_assert(sl);
  tor_assert(idx>=0);
  tor_assert(idx < sl->num_used);
  --sl->num_used;
  if (idx < sl->num_used)
    memmove(sl->list+idx, sl->list+idx+1, sizeof(void*)*(sl->num_used-idx));
}

/** Insert the value <b>val</b> as the new <b>idx</b>th element of
 * <b>sl</b>, moving all items previously at <b>idx</b> or later
 * forward one space.
 */
void
smartlist_insert(smartlist_t *sl, int idx, void *val)
{
  tor_assert(sl);
  tor_assert(idx>=0);
  tor_assert(idx <= sl->num_used);
  if (idx == sl->num_used) {
    smartlist_add(sl, val);
  } else {
    smartlist_ensure_capacity(sl, sl->num_used+1);
    /* Move other elements away */
    if (idx < sl->num_used)
      memmove(sl->list + idx + 1, sl->list + idx,
              sizeof(void*)*(sl->num_used-idx));
    sl->num_used++;
    sl->list[idx] = val;
  }
}

/**
 * Split a string <b>str</b> along all occurrences of <b>sep</b>,
 * adding the split strings, in order, to <b>sl</b>.
 *
 * If <b>flags</b>&amp;SPLIT_SKIP_SPACE is true, remove initial and
 * trailing space from each entry.
 * If <b>flags</b>&amp;SPLIT_IGNORE_BLANK is true, remove any entries
 * of length 0.
 * If <b>flags</b>&amp;SPLIT_STRIP_SPACE is true, strip spaces from each
 * split string.
 *
 * If max>0, divide the string into no more than <b>max</b> pieces. If
 * <b>sep</b> is NULL, split on any sequence of horizontal space.
 */
int
smartlist_split_string(smartlist_t *sl, const char *str, const char *sep,
                       int flags, int max)
{
  const char *cp, *end, *next;
  int n = 0;

  tor_assert(sl);
  tor_assert(str);

  cp = str;
  while (1) {
    if (flags&SPLIT_SKIP_SPACE) {
      while (TOR_ISSPACE(*cp)) ++cp;
    }

    if (max>0 && n == max-1) {
      end = strchr(cp,'\0');
    } else if (sep) {
      end = strstr(cp,sep);
      if (!end)
        end = strchr(cp,'\0');
    } else {
      for (end = cp; *end && *end != '\t' && *end != ' '; ++end)
        ;
    }

    tor_assert(end);

    if (!*end) {
      next = NULL;
    } else if (sep) {
      next = end+strlen(sep);
    } else {
      next = end+1;
      while (*next == '\t' || *next == ' ')
        ++next;
    }

    if (flags&SPLIT_SKIP_SPACE) {
      while (end > cp && TOR_ISSPACE(*(end-1)))
        --end;
    }
    if (end != cp || !(flags&SPLIT_IGNORE_BLANK)) {
      char *string = tor_strndup(cp, end-cp);
      if (flags&SPLIT_STRIP_SPACE)
        tor_strstrip(string, " ");
      smartlist_add(sl, string);
      ++n;
    }
    if (!next)
      break;
    cp = next;
  }

  return n;
}

/** Allocate and return a new string containing the concatenation of
 * the elements of <b>sl</b>, in order, separated by <b>join</b>.  If
 * <b>terminate</b> is true, also terminate the string with <b>join</b>.
 * If <b>len_out</b> is not NULL, set <b>len_out</b> to the length of
 * the returned string. Requires that every element of <b>sl</b> is
 * NUL-terminated string.
 */
char *
smartlist_join_strings(smartlist_t *sl, const char *join,
                       int terminate, size_t *len_out)
{
  return smartlist_join_strings2(sl,join,strlen(join),terminate,len_out);
}

/** As smartlist_join_strings, but instead of separating/terminated with a
 * NUL-terminated string <b>join</b>, uses the <b>join_len</b>-byte sequence
 * at <b>join</b>.  (Useful for generating a sequence of NUL-terminated
 * strings.)
 */
char *
smartlist_join_strings2(smartlist_t *sl, const char *join,
                        size_t join_len, int terminate, size_t *len_out)
{
  int i;
  size_t n = 0;
  char *r = NULL, *dst, *src;

  tor_assert(sl);
  tor_assert(join);

  if (terminate)
    n = join_len;

  for (i = 0; i < sl->num_used; ++i) {
    n += strlen(sl->list[i]);
    if (i+1 < sl->num_used) /* avoid double-counting the last one */
      n += join_len;
  }
  dst = r = tor_malloc(n+1);
  for (i = 0; i < sl->num_used; ) {
    for (src = sl->list[i]; *src; )
      *dst++ = *src++;
    if (++i < sl->num_used) {
      memcpy(dst, join, join_len);
      dst += join_len;
    }
  }
  if (terminate) {
    memcpy(dst, join, join_len);
    dst += join_len;
  }
  *dst = '\0';

  if (len_out)
    *len_out = dst-r;
  return r;
}

/** Sort the members of <b>sl</b> into an order defined by
 * the ordering function <b>compare</b>, which returns less then 0 if a
 * precedes b, greater than 0 if b precedes a, and 0 if a 'equals' b.
 */
void
smartlist_sort(smartlist_t *sl, int (*compare)(const void **a, const void **b))
{
  if (!sl->num_used)
    return;
  qsort(sl->list, sl->num_used, sizeof(void*),
        (int (*)(const void *,const void*))compare);
}

/** Given a sorted smartlist <b>sl</b> and the comparison function used to
 * sort it, remove all duplicate members.  If free_fn is provided, calls
 * free_fn on each duplicate.  Otherwise, just removes them.  Preserves order.
 */
void
smartlist_uniq(smartlist_t *sl,
               int (*compare)(const void **a, const void **b),
               void (*free_fn)(void *a))
{
  int i;
  for (i=1; i < sl->num_used; ++i) {
    if (compare((const void **)&(sl->list[i-1]),
                (const void **)&(sl->list[i])) == 0) {
      if (free_fn)
        free_fn(sl->list[i]);
      smartlist_del_keeporder(sl, i--);
    }
  }
}

/** Assuming the members of <b>sl</b> are in order, return a pointer to the
 * member that matches <b>key</b>.  Ordering and matching are defined by a
 * <b>compare</b> function that returns 0 on a match; less than 0 if key is
 * less than member, and greater than 0 if key is greater then member.
 */
void *
smartlist_bsearch(smartlist_t *sl, const void *key,
                  int (*compare)(const void *key, const void **member))
{
  int found, idx;
  idx = smartlist_bsearch_idx(sl, key, compare, &found);
  return found ? smartlist_get(sl, idx) : NULL;
}

/** Assuming the members of <b>sl</b> are in order, return the index of the
 * member that matches <b>key</b>.  If no member matches, return the index of
 * the first member greater than <b>key</b>, or smartlist_len(sl) if no member
 * is greater than <b>key</b>.  Set <b>found_out</b> to true on a match, to
 * false otherwise.  Ordering and matching are defined by a <b>compare</b>
 * function that returns 0 on a match; less than 0 if key is less than member,
 * and greater than 0 if key is greater then member.
 */
int
smartlist_bsearch_idx(const smartlist_t *sl, const void *key,
                      int (*compare)(const void *key, const void **member),
                      int *found_out)
{
  int hi = smartlist_len(sl) - 1, lo = 0, cmp, mid;

  while (lo <= hi) {
    mid = (lo + hi) / 2;
    cmp = compare(key, (const void**) &(sl->list[mid]));
    if (cmp>0) { /* key > sl[mid] */
      lo = mid+1;
    } else if (cmp<0) { /* key < sl[mid] */
      hi = mid-1;
    } else { /* key == sl[mid] */
      *found_out = 1;
      return mid;
    }
  }
  /* lo > hi. */
  {
    tor_assert(lo >= 0);
    if (lo < smartlist_len(sl)) {
      cmp = compare(key, (const void**) &(sl->list[lo]));
      tor_assert(cmp < 0);
    } else if (smartlist_len(sl)) {
      cmp = compare(key, (const void**) &(sl->list[smartlist_len(sl)-1]));
      tor_assert(cmp > 0);
    }
  }
  *found_out = 0;
  return lo;
}

/** Helper: compare two const char **s. */
static int
_compare_string_ptrs(const void **_a, const void **_b)
{
  return strcmp((const char*)*_a, (const char*)*_b);
}

/** Sort a smartlist <b>sl</b> containing strings into lexically ascending
 * order. */
void
smartlist_sort_strings(smartlist_t *sl)
{
  smartlist_sort(sl, _compare_string_ptrs);
}

/** Remove duplicate strings from a sorted list, and free them with tor_free().
 */
void
smartlist_uniq_strings(smartlist_t *sl)
{
  smartlist_uniq(sl, _compare_string_ptrs, _tor_free);
}

/* Heap-based priority queue implementation for O(lg N) insert and remove.
 * Recall that the heap property is that, for every index I, h[I] <
 * H[LEFT_CHILD[I]] and h[I] < H[RIGHT_CHILD[I]].
 */

/* For a 1-indexed array, we would use LEFT_CHILD[x] = 2*x and RIGHT_CHILD[x]
 * = 2*x + 1.  But this is C, so we have to adjust a little. */
//#define LEFT_CHILD(i)  ( ((i)+1)*2 - 1)
//#define RIGHT_CHILD(i) ( ((i)+1)*2 )
//#define PARENT(i)      ( ((i)+1)/2 - 1)
#define LEFT_CHILD(i)  ( 2*(i) + 1 )
#define RIGHT_CHILD(i) ( 2*(i) + 2 )
#define PARENT(i)      ( ((i)-1) / 2 )

/** Helper. <b>sl</b> may have at most one violation of the heap property:
 * the item at <b>idx</b> may be greater than one or both of its children.
 * Restore the heap property. */
static INLINE void
smartlist_heapify(smartlist_t *sl,
                  int (*compare)(const void *a, const void *b),
                  int idx)
{
  while (1) {
    int left_idx = LEFT_CHILD(idx);
    int best_idx;

    if (left_idx >= sl->num_used)
      return;
    if (compare(sl->list[idx],sl->list[left_idx]) < 0)
      best_idx = idx;
    else
      best_idx = left_idx;
    if (left_idx+1 < sl->num_used &&
        compare(sl->list[left_idx+1],sl->list[best_idx]) < 0)
      best_idx = left_idx + 1;

    if (best_idx == idx) {
      return;
    } else {
      void *tmp = sl->list[idx];
      sl->list[idx] = sl->list[best_idx];
      sl->list[best_idx] = tmp;

      idx = best_idx;
    }
  }
}

/** Insert <b>item</b> into the heap stored in <b>sl</b>, where order
 * is determined by <b>compare</b>. */
void
smartlist_pqueue_add(smartlist_t *sl,
                     int (*compare)(const void *a, const void *b),
                     void *item)
{
  int idx;
  smartlist_add(sl,item);

  for (idx = sl->num_used - 1; idx; ) {
    int parent = PARENT(idx);
    if (compare(sl->list[idx], sl->list[parent]) < 0) {
      void *tmp = sl->list[parent];
      sl->list[parent] = sl->list[idx];
      sl->list[idx] = tmp;
      idx = parent;
    } else {
      return;
    }
  }
}

/** Remove and return the top-priority item from the heap stored in <b>sl</b>,
 * where order is determined by <b>compare</b>.  <b>sl</b> must not be
 * empty. */
void *
smartlist_pqueue_pop(smartlist_t *sl,
                     int (*compare)(const void *a, const void *b))
{
  void *top;
  tor_assert(sl->num_used);

  top = sl->list[0];
  if (--sl->num_used) {
    sl->list[0] = sl->list[sl->num_used];
    smartlist_heapify(sl, compare, 0);
  }
  return top;
}

/** Assert that the heap property is correctly maintained by the heap stored
 * in <b>sl</b>, where order is determined by <b>compare</b>. */
void
smartlist_pqueue_assert_ok(smartlist_t *sl,
                           int (*compare)(const void *a, const void *b))
{
  int i;
  for (i = sl->num_used - 1; i > 0; --i) {
    tor_assert(compare(sl->list[PARENT(i)], sl->list[i]) <= 0);
  }
}

/** Helper: compare two DIGEST_LEN digests. */
static int
_compare_digests(const void **_a, const void **_b)
{
  return tor_memcmp((const char*)*_a, (const char*)*_b, DIGEST_LEN);
}

/** Sort the list of DIGEST_LEN-byte digests into ascending order. */
void
smartlist_sort_digests(smartlist_t *sl)
{
  smartlist_sort(sl, _compare_digests);
}

/** Remove duplicate digests from a sorted list, and free them with tor_free().
 */
void
smartlist_uniq_digests(smartlist_t *sl)
{
  smartlist_uniq(sl, _compare_digests, _tor_free);
}

/** Helper: Declare an entry type and a map type to implement a mapping using
 * ht.h.  The map type will be called <b>maptype</b>.  The key part of each
 * entry is declared using the C declaration <b>keydecl</b>.  All functions
 * and types associated with the map get prefixed with <b>prefix</b> */
#define DEFINE_MAP_STRUCTS(maptype, keydecl, prefix)      \
  typedef struct prefix ## entry_t {                      \
    HT_ENTRY(prefix ## entry_t) node;                     \
    void *val;                                            \
    keydecl;                                              \
  } prefix ## entry_t;                                    \
  struct maptype {                                        \
    HT_HEAD(prefix ## impl, prefix ## entry_t) head;      \
  }

DEFINE_MAP_STRUCTS(strmap_t, char *key, strmap_);
DEFINE_MAP_STRUCTS(digestmap_t, char key[DIGEST_LEN], digestmap_);

/** Helper: compare strmap_entry_t objects by key value. */
static INLINE int
strmap_entries_eq(const strmap_entry_t *a, const strmap_entry_t *b)
{
  return !strcmp(a->key, b->key);
}

/** Helper: return a hash value for a strmap_entry_t. */
static INLINE unsigned int
strmap_entry_hash(const strmap_entry_t *a)
{
  return ht_string_hash(a->key);
}

/** Helper: compare digestmap_entry_t objects by key value. */
static INLINE int
digestmap_entries_eq(const digestmap_entry_t *a, const digestmap_entry_t *b)
{
  return tor_memeq(a->key, b->key, DIGEST_LEN);
}

/** Helper: return a hash value for a digest_map_t. */
static INLINE unsigned int
digestmap_entry_hash(const digestmap_entry_t *a)
{
#if SIZEOF_INT != 8
  const uint32_t *p = (const uint32_t*)a->key;
  return p[0] ^ p[1] ^ p[2] ^ p[3] ^ p[4];
#else
  const uint64_t *p = (const uint64_t*)a->key;
  return p[0] ^ p[1];
#endif
}

HT_PROTOTYPE(strmap_impl, strmap_entry_t, node, strmap_entry_hash,
             strmap_entries_eq)
HT_GENERATE(strmap_impl, strmap_entry_t, node, strmap_entry_hash,
            strmap_entries_eq, 0.6, malloc, realloc, free)

HT_PROTOTYPE(digestmap_impl, digestmap_entry_t, node, digestmap_entry_hash,
             digestmap_entries_eq)
HT_GENERATE(digestmap_impl, digestmap_entry_t, node, digestmap_entry_hash,
            digestmap_entries_eq, 0.6, malloc, realloc, free)

/** Constructor to create a new empty map from strings to void*'s.
 */
strmap_t *
strmap_new(void)
{
  strmap_t *result;
  result = tor_malloc(sizeof(strmap_t));
  HT_INIT(strmap_impl, &result->head);
  return result;
}

/** Constructor to create a new empty map from digests to void*'s.
 */
digestmap_t *
digestmap_new(void)
{
  digestmap_t *result;
  result = tor_malloc(sizeof(digestmap_t));
  HT_INIT(digestmap_impl, &result->head);
  return result;
}

/** Set the current value for <b>key</b> to <b>val</b>.  Returns the previous
 * value for <b>key</b> if one was set, or NULL if one was not.
 *
 * This function makes a copy of <b>key</b> if necessary, but not of
 * <b>val</b>.
 */
void *
strmap_set(strmap_t *map, const char *key, void *val)
{
  strmap_entry_t *resolve;
  strmap_entry_t search;
  void *oldval;
  tor_assert(map);
  tor_assert(key);
  tor_assert(val);
  search.key = (char*)key;
  resolve = HT_FIND(strmap_impl, &map->head, &search);
  if (resolve) {
    oldval = resolve->val;
    resolve->val = val;
    return oldval;
  } else {
    resolve = tor_malloc_zero(sizeof(strmap_entry_t));
    resolve->key = tor_strdup(key);
    resolve->val = val;
    tor_assert(!HT_FIND(strmap_impl, &map->head, resolve));
    HT_INSERT(strmap_impl, &map->head, resolve);
    return NULL;
  }
}

#define OPTIMIZED_DIGESTMAP_SET

/** Like strmap_set() above but for digestmaps. */
void *
digestmap_set(digestmap_t *map, const char *key, void *val)
{
#ifndef OPTIMIZED_DIGESTMAP_SET
  digestmap_entry_t *resolve;
#endif
  digestmap_entry_t search;
  void *oldval;
  tor_assert(map);
  tor_assert(key);
  tor_assert(val);
  memcpy(&search.key, key, DIGEST_LEN);
#ifndef OPTIMIZED_DIGESTMAP_SET
  resolve = HT_FIND(digestmap_impl, &map->head, &search);
  if (resolve) {
    oldval = resolve->val;
    resolve->val = val;
    return oldval;
  } else {
    resolve = tor_malloc_zero(sizeof(digestmap_entry_t));
    memcpy(resolve->key, key, DIGEST_LEN);
    resolve->val = val;
    HT_INSERT(digestmap_impl, &map->head, resolve);
    return NULL;
  }
#else
  /* We spend up to 5% of our time in this function, so the code below is
   * meant to optimize the check/alloc/set cycle by avoiding the two trips to
   * the hash table that we do in the unoptimized code above.  (Each of
   * HT_INSERT and HT_FIND calls HT_SET_HASH and HT_FIND_P.)
   */
  _HT_FIND_OR_INSERT(digestmap_impl, node, digestmap_entry_hash, &(map->head),
         digestmap_entry_t, &search, ptr,
         {
            /* we found an entry. */
            oldval = (*ptr)->val;
            (*ptr)->val = val;
            return oldval;
         },
         {
           /* We didn't find the entry. */
           digestmap_entry_t *newent =
             tor_malloc_zero(sizeof(digestmap_entry_t));
           memcpy(newent->key, key, DIGEST_LEN);
           newent->val = val;
           _HT_FOI_INSERT(node, &(map->head), &search, newent, ptr);
           return NULL;
         });
#endif
}

/** Return the current value associated with <b>key</b>, or NULL if no
 * value is set.
 */
void *
strmap_get(const strmap_t *map, const char *key)
{
  strmap_entry_t *resolve;
  strmap_entry_t search;
  tor_assert(map);
  tor_assert(key);
  search.key = (char*)key;
  resolve = HT_FIND(strmap_impl, &map->head, &search);
  if (resolve) {
    return resolve->val;
  } else {
    return NULL;
  }
}

/** Like strmap_get() above but for digestmaps. */
void *
digestmap_get(const digestmap_t *map, const char *key)
{
  digestmap_entry_t *resolve;
  digestmap_entry_t search;
  tor_assert(map);
  tor_assert(key);
  memcpy(&search.key, key, DIGEST_LEN);
  resolve = HT_FIND(digestmap_impl, &map->head, &search);
  if (resolve) {
    return resolve->val;
  } else {
    return NULL;
  }
}

/** Remove the value currently associated with <b>key</b> from the map.
 * Return the value if one was set, or NULL if there was no entry for
 * <b>key</b>.
 *
 * Note: you must free any storage associated with the returned value.
 */
void *
strmap_remove(strmap_t *map, const char *key)
{
  strmap_entry_t *resolve;
  strmap_entry_t search;
  void *oldval;
  tor_assert(map);
  tor_assert(key);
  search.key = (char*)key;
  resolve = HT_REMOVE(strmap_impl, &map->head, &search);
  if (resolve) {
    oldval = resolve->val;
    tor_free(resolve->key);
    tor_free(resolve);
    return oldval;
  } else {
    return NULL;
  }
}

/** Like strmap_remove() above but for digestmaps. */
void *
digestmap_remove(digestmap_t *map, const char *key)
{
  digestmap_entry_t *resolve;
  digestmap_entry_t search;
  void *oldval;
  tor_assert(map);
  tor_assert(key);
  memcpy(&search.key, key, DIGEST_LEN);
  resolve = HT_REMOVE(digestmap_impl, &map->head, &search);
  if (resolve) {
    oldval = resolve->val;
    tor_free(resolve);
    return oldval;
  } else {
    return NULL;
  }
}

/** Same as strmap_set, but first converts <b>key</b> to lowercase. */
void *
strmap_set_lc(strmap_t *map, const char *key, void *val)
{
  /* We could be a little faster by using strcasecmp instead, and a separate
   * type, but I don't think it matters. */
  void *v;
  char *lc_key = tor_strdup(key);
  tor_strlower(lc_key);
  v = strmap_set(map,lc_key,val);
  tor_free(lc_key);
  return v;
}

/** Same as strmap_get, but first converts <b>key</b> to lowercase. */
void *
strmap_get_lc(const strmap_t *map, const char *key)
{
  void *v;
  char *lc_key = tor_strdup(key);
  tor_strlower(lc_key);
  v = strmap_get(map,lc_key);
  tor_free(lc_key);
  return v;
}

/** Same as strmap_remove, but first converts <b>key</b> to lowercase */
void *
strmap_remove_lc(strmap_t *map, const char *key)
{
  void *v;
  char *lc_key = tor_strdup(key);
  tor_strlower(lc_key);
  v = strmap_remove(map,lc_key);
  tor_free(lc_key);
  return v;
}

/** return an <b>iterator</b> pointer to the front of a map.
 *
 * Iterator example:
 *
 * \code
 * // uppercase values in "map", removing empty values.
 *
 * strmap_iter_t *iter;
 * const char *key;
 * void *val;
 * char *cp;
 *
 * for (iter = strmap_iter_init(map); !strmap_iter_done(iter); ) {
 *    strmap_iter_get(iter, &key, &val);
 *    cp = (char*)val;
 *    if (!*cp) {
 *       iter = strmap_iter_next_rmv(map,iter);
 *       free(val);
 *    } else {
 *       for (;*cp;cp++) *cp = TOR_TOUPPER(*cp);
 *       iter = strmap_iter_next(map,iter);
 *    }
 * }
 * \endcode
 *
 */
strmap_iter_t *
strmap_iter_init(strmap_t *map)
{
  tor_assert(map);
  return HT_START(strmap_impl, &map->head);
}

/** Start iterating through <b>map</b>.  See strmap_iter_init() for example. */
digestmap_iter_t *
digestmap_iter_init(digestmap_t *map)
{
  tor_assert(map);
  return HT_START(digestmap_impl, &map->head);
}

/** Advance the iterator <b>iter</b> for <b>map</b> a single step to the next
 * entry, and return its new value. */
strmap_iter_t *
strmap_iter_next(strmap_t *map, strmap_iter_t *iter)
{
  tor_assert(map);
  tor_assert(iter);
  return HT_NEXT(strmap_impl, &map->head, iter);
}

/** Advance the iterator <b>iter</b> for map a single step to the next entry,
 * and return its new value. */
digestmap_iter_t *
digestmap_iter_next(digestmap_t *map, digestmap_iter_t *iter)
{
  tor_assert(map);
  tor_assert(iter);
  return HT_NEXT(digestmap_impl, &map->head, iter);
}

/** Advance the iterator <b>iter</b> a single step to the next entry, removing
 * the current entry, and return its new value.
 */
strmap_iter_t *
strmap_iter_next_rmv(strmap_t *map, strmap_iter_t *iter)
{
  strmap_entry_t *rmv;
  tor_assert(map);
  tor_assert(iter);
  tor_assert(*iter);
  rmv = *iter;
  iter = HT_NEXT_RMV(strmap_impl, &map->head, iter);
  tor_free(rmv->key);
  tor_free(rmv);
  return iter;
}

/** Advance the iterator <b>iter</b> a single step to the next entry, removing
 * the current entry, and return its new value.
 */
digestmap_iter_t *
digestmap_iter_next_rmv(digestmap_t *map, digestmap_iter_t *iter)
{
  digestmap_entry_t *rmv;
  tor_assert(map);
  tor_assert(iter);
  tor_assert(*iter);
  rmv = *iter;
  iter = HT_NEXT_RMV(digestmap_impl, &map->head, iter);
  tor_free(rmv);
  return iter;
}

/** Set *<b>keyp</b> and *<b>valp</b> to the current entry pointed to by
 * iter. */
void
strmap_iter_get(strmap_iter_t *iter, const char **keyp, void **valp)
{
  tor_assert(iter);
  tor_assert(*iter);
  tor_assert(keyp);
  tor_assert(valp);
  *keyp = (*iter)->key;
  *valp = (*iter)->val;
}

/** Set *<b>keyp</b> and *<b>valp</b> to the current entry pointed to by
 * iter. */
void
digestmap_iter_get(digestmap_iter_t *iter, const char **keyp, void **valp)
{
  tor_assert(iter);
  tor_assert(*iter);
  tor_assert(keyp);
  tor_assert(valp);
  *keyp = (*iter)->key;
  *valp = (*iter)->val;
}

/** Return true iff <b>iter</b> has advanced past the last entry of
 * <b>map</b>. */
int
strmap_iter_done(strmap_iter_t *iter)
{
  return iter == NULL;
}

/** Return true iff <b>iter</b> has advanced past the last entry of
 * <b>map</b>. */
int
digestmap_iter_done(digestmap_iter_t *iter)
{
  return iter == NULL;
}

/** Remove all entries from <b>map</b>, and deallocate storage for those
 * entries.  If free_val is provided, it is invoked on every value in
 * <b>map</b>.
 */
void
strmap_free(strmap_t *map, void (*free_val)(void*))
{
  strmap_entry_t **ent, **next, *this;
  for (ent = HT_START(strmap_impl, &map->head); ent != NULL; ent = next) {
    this = *ent;
    next = HT_NEXT_RMV(strmap_impl, &map->head, ent);
    tor_free(this->key);
    if (free_val)
      free_val(this->val);
    tor_free(this);
  }
  tor_assert(HT_EMPTY(&map->head));
  HT_CLEAR(strmap_impl, &map->head);
  tor_free(map);
}

/** Remove all entries from <b>map</b>, and deallocate storage for those
 * entries.  If free_val is provided, it is invoked on every value in
 * <b>map</b>.
 */
void
digestmap_free(digestmap_t *map, void (*free_val)(void*))
{
  digestmap_entry_t **ent, **next, *this;
  for (ent = HT_START(digestmap_impl, &map->head); ent != NULL; ent = next) {
    this = *ent;
    next = HT_NEXT_RMV(digestmap_impl, &map->head, ent);
    if (free_val)
      free_val(this->val);
    tor_free(this);
  }
  tor_assert(HT_EMPTY(&map->head));
  HT_CLEAR(digestmap_impl, &map->head);
  tor_free(map);
}

/** Fail with an assertion error if anything has gone wrong with the internal
 * representation of <b>map</b>. */
void
strmap_assert_ok(const strmap_t *map)
{
  tor_assert(!_strmap_impl_HT_REP_IS_BAD(&map->head));
}
/** Fail with an assertion error if anything has gone wrong with the internal
 * representation of <b>map</b>. */
void
digestmap_assert_ok(const digestmap_t *map)
{
  tor_assert(!_digestmap_impl_HT_REP_IS_BAD(&map->head));
}

/** Return true iff <b>map</b> has no entries. */
int
strmap_isempty(const strmap_t *map)
{
  return HT_EMPTY(&map->head);
}

/** Return true iff <b>map</b> has no entries. */
int
digestmap_isempty(const digestmap_t *map)
{
  return HT_EMPTY(&map->head);
}

/** Return the number of items in <b>map</b>. */
int
strmap_size(const strmap_t *map)
{
  return HT_SIZE(&map->head);
}

/** Return the number of items in <b>map</b>. */
int
digestmap_size(const digestmap_t *map)
{
  return HT_SIZE(&map->head);
}

/** Declare a function called <b>funcname</b> that acts as a find_nth_FOO
 * function for an array of type <b>elt_t</b>*.
 *
 * NOTE: The implementation kind of sucks: It's O(n log n), whereas finding
 * the kth element of an n-element list can be done in O(n).  Then again, this
 * implementation is not in critical path, and it is obviously correct. */
#define IMPLEMENT_ORDER_FUNC(funcname, elt_t)                   \
  static int                                                    \
  _cmp_ ## elt_t(const void *_a, const void *_b)                \
  {                                                             \
    const elt_t *a = _a, *b = _b;                               \
    if (*a<*b)                                                  \
      return -1;                                                \
    else if (*a>*b)                                             \
      return 1;                                                 \
    else                                                        \
      return 0;                                                 \
  }                                                             \
  elt_t                                                         \
  funcname(elt_t *array, int n_elements, int nth)               \
  {                                                             \
    tor_assert(nth >= 0);                                       \
    tor_assert(nth < n_elements);                               \
    qsort(array, n_elements, sizeof(elt_t), _cmp_ ##elt_t);     \
    return array[nth];                                          \
  }

IMPLEMENT_ORDER_FUNC(find_nth_int, int)
IMPLEMENT_ORDER_FUNC(find_nth_time, time_t)
IMPLEMENT_ORDER_FUNC(find_nth_double, double)
IMPLEMENT_ORDER_FUNC(find_nth_uint32, uint32_t)
IMPLEMENT_ORDER_FUNC(find_nth_long, long)

/** Return a newly allocated digestset_t, optimized to hold a total of
 * <b>max_elements</b> digests with a reasonably low false positive weight. */
digestset_t *
digestset_new(int max_elements)
{
  /* The probability of false positives is about P=(1 - exp(-kn/m))^k, where k
   * is the number of hash functions per entry, m is the bits in the array,
   * and n is the number of elements inserted.  For us, k==4, n<=max_elements,
   * and m==n_bits= approximately max_elements*32.  This gives
   *   P<(1-exp(-4*n/(32*n)))^4 == (1-exp(1/-8))^4 == .00019
   *
   * It would be more optimal in space vs false positives to get this false
   * positive rate by going for k==13, and m==18.5n, but we also want to
   * conserve CPU, and k==13 is pretty big.
   */
  int n_bits = 1u << (tor_log2(max_elements)+5);
  digestset_t *r = tor_malloc(sizeof(digestset_t));
  r->mask = n_bits - 1;
  r->ba = bitarray_init_zero(n_bits);
  return r;
}

/** Free all storage held in <b>set</b>. */
void
digestset_free(digestset_t *set)
{
  bitarray_free(set->ba);
  tor_free(set);
}