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
/* bt.c: BIT TABLES
 *
 * $Id: //info.ravenbrook.com/project/mps/master/code/bt.c#21 $
 * Copyright (c) 2001-2020 Ravenbrook Limited.  See end of file for license.
 *
 * READERSHIP
 *
 * .readership: Any MPS developer
 *
 * DESIGN
 *
 * .design: see <design/bt>
 *
 * .aver.critical: The function BTIsResRange (and anything it calls)
 * is on the critical path <design/critical-path> because it is
 * called by NailboardIsResRange, which is called for every object in
 * a nailboarded segment when the segment is scanned or reclaimed; see
 * <design/nailboard#.impl.isresrange>.
 */

#include "bt.h"
#include "config.h"
#include "check.h"
#include "mpm.h"

SRCID(bt, "$Id: //info.ravenbrook.com/project/mps/master/code/bt.c#21 $");


/* BTIndexAlignUp, BTIndexAlignDown -- Align bit-table indices
 *
 * Align bit-table indices up and down to word boundaries
 */

#define BTIndexAlignUp(index) (IndexAlignUp((index), MPS_WORD_WIDTH))
#define BTIndexAlignDown(index) (IndexAlignDown((index), MPS_WORD_WIDTH))


/* BTMask -- generate sub-word masks
 *
 * Create a mask with only specified bits set
 */

/* Return a word mask of bits set only from base and above */
#define BTMaskLow(base) (~(Word)0 << (base))

/* Return a word mask of bits set only below limit */
#define BTMaskHigh(limit) (~(Word)0 >> (MPS_WORD_WIDTH - (limit)))

/* Return a word mask of bits set only in requested range */
#define BTMask(base,limit) (BTMaskHigh((limit)) & BTMaskLow((base)))


/* BTWordIndex, BTBitIndex -- Decode BT indexes
 *
 * Return word and bit indexes from index
 */

#define BTWordIndex(index) ((index) >> MPS_WORD_SHIFT)
#define BTBitIndex(index) ((index) & (MPS_WORD_WIDTH - 1))


/* BTIsSmallRange -- test range size
 *
 * Predicate to determine whether a range is sufficiently small
 * that it's not worth trying to separate words and odd bits.
 * The choice of what counts as "sufficiently small" is made
 * for efficiency reasons. Empirical evidence indicates that
 * a good choice is ranges of size 6 or less.
 */

#define BTIsSmallRange(base,limit) ((base) + 6 >= (limit))


/* ACT_ON_RANGE -- macro to act on a base-limit range
 *
 * Three actions should be provided:
 *   - single_action(btIndex) - operates on a single bit
 *   - bits_action(wordIndex, base, limit) -- operates on part-words
 *   - word_action(wordIndex) -- Operates on full words in range
 * WORD_ACTIONs should not use break or continue.
 *
 * If the range is small enough it will be processed a single
 * bit at a time. Larger ranges are processed as words where
 * possible, and part-words for boundary bits.
 */

#define ACT_ON_RANGE(base,limit,single_action, \
                     bits_action,word_action) \
  BEGIN \
    if (BTIsSmallRange((base), (limit))) { \
      /* Small ranges are processed most efficiently bit-by-bit */ \
      Index actBit; \
      for (actBit = (base); actBit < (limit); ++actBit) { \
        single_action(actBit); \
      } \
    } else { \
      Index actInnerBase = BTIndexAlignUp((base)); \
      if (actInnerBase > (limit)) { /* no inner range */ \
        /* Must have base < limit otherwise caught by small range case */ \
        /* And see .aver.critical. */ \
        AVER_CRITICAL((base) < (limit)); \
        bits_action(BTWordIndex((base)), \
                    BTBitIndex((base)), \
                    BTBitIndex((limit))); \
      } else { \
        Index actInnerLimit = BTIndexAlignDown((limit)); \
        Index actWordIndex, actWordBase, actWordLimit; \
\
        actWordBase = BTWordIndex(actInnerBase); \
        actWordLimit = BTWordIndex(actInnerLimit); \
\
        if ((base) < actInnerBase) { \
          bits_action(actWordBase-1, \
                      BTBitIndex((base)), \
                      MPS_WORD_WIDTH); \
        } \
\
        for (actWordIndex = actWordBase; actWordIndex < actWordLimit; \
            ++actWordIndex) { \
          word_action(actWordIndex); \
        } \
\
        if ((limit) > actInnerLimit) { \
          bits_action(actWordLimit, 0, BTBitIndex((limit))); \
        } \
      } \
    } \
  END


/* ACT_ON_RANGE_HIGH -- macro to act on a base-limit range
 *
 * in reverse order. Usage as for ACT_ON_RANGE
 */

#define ACT_ON_RANGE_HIGH(base,limit,single_action, \
                          bits_action,word_action) \
  BEGIN \
    if (BTIsSmallRange((base), (limit))) { \
      /* Small ranges are processed most efficiently bit-by-bit */ \
      Index actBit; \
      for (actBit = (limit); actBit > (base); --actBit) { \
        single_action(actBit - 1); \
      } \
    } else { \
      Index actInnerBase = BTIndexAlignUp((base)); \
      if (actInnerBase > (limit)) { /* no inner range */ \
        AVER((base) < (limit)); /* caught by small range case */ \
        bits_action(BTWordIndex((base)), \
                    BTBitIndex((base)), \
                    BTBitIndex((limit))); \
      } else { \
        Index actInnerLimit = BTIndexAlignDown((limit)); \
        Index actWordIndex, actWordBase, actWordLimit; \
\
        actWordBase = BTWordIndex(actInnerBase); \
        actWordLimit = BTWordIndex(actInnerLimit); \
\
        if ((limit) > actInnerLimit) { \
          bits_action(actWordLimit, 0, BTBitIndex((limit))); \
        } \
\
        for (actWordIndex = actWordLimit; actWordIndex > actWordBase; \
            --actWordIndex) { \
          word_action(actWordIndex-1); \
        } \
\
        if ((base) < actInnerBase) { \
          bits_action(actWordBase-1, \
                      BTBitIndex((base)), \
                      MPS_WORD_WIDTH); \
        } \
      } \
    } \
  END



/* BTCreate -- allocate a BT from the control pool
 *
 * <design/bt#.if.create>
 */

Res BTCreate(BT *btReturn, Arena arena, Count length)
{
  Res res;
  BT bt;
  void *p;

  AVER(btReturn != NULL);
  AVERT(Arena, arena);
  AVER(length > 0);

  res = ControlAlloc(&p, arena, BTSize(length));
  if (res != ResOK)
    return res;
  bt = (BT)p;

  *btReturn = bt;
  return ResOK;
}


/* BTDestroy -- free a BT to the control pool.
 *
 * <design/bt#.if.destroy>
 */

void BTDestroy(BT bt, Arena arena, Count length)
{
  AVER(bt != NULL);
  AVERT(Arena, arena);
  AVER(length > 0);

  ControlFree(arena, bt, BTSize(length));
}


/* BTCheck -- check the validity of a bit table
 *
 * There's not much that can be checked at present.  This is
 * discussed in review.impl.c.bt.4.
 */

Bool BTCheck(BT bt)
{
  AVER(bt != NULL);
  AVER(AddrIsAligned((Addr)bt, sizeof(Word)));
  return TRUE;
}


/* BTSize -- return the size of a BT
 *
 * <design/bt#.fun.size>
 */

Size (BTSize)(Count n)
{
  /* check that the expression used in rounding up doesn't overflow */
  AVER(n+MPS_WORD_WIDTH-1 > n);

  return BTSize(n);
}


/* BTGet -- get a bit from a BT
 *
 * <design/bt#.fun.get>
 */

Bool (BTGet)(BT t, Index i)
{
  AVERT(BT, t);
  /* Can't check i */

  /* see macro in <code/mpm.h> */
  return BTGet(t, i);
}


/* BTSet -- set a bit in a BT
 *
 * <design/bt#.fun.set>
 */

void (BTSet)(BT t, Index i)
{
  AVERT(BT, t);
  /* Can't check i */

  /* see macro in <code/mpm.h> */
  BTSet(t, i);
}


/* BTRes -- reset a bit in a BT
 *
 * <design/bt#.fun.res>
 */

void (BTRes)(BT t, Index i)
{
  AVERT(BT, t);
  /* Can't check i */

  /* see macro in <code/mpm.h> */
  BTRes(t, i);
}


/* BTSetRange -- set a range of bits in a BT
 *
 * <design/bt#.fun.set-range>
 */

void BTSetRange(BT t, Index base, Index limit)
{
  AVERT(BT, t);
  AVER(base < limit);

#define SINGLE_SET_RANGE(i) \
  BTSet(t, (i))
#define BITS_SET_RANGE(i,base,limit) \
  t[(i)] |= BTMask((base),(limit))
#define WORD_SET_RANGE(i) \
  t[(i)] = ~(Word)(0)

  ACT_ON_RANGE(base, limit, SINGLE_SET_RANGE,
               BITS_SET_RANGE, WORD_SET_RANGE);
}


/* BTIsResRange -- test whether a range of bits is all reset
 *
 * <design/bt#.fun.is-reset-range>.
 */

Bool BTIsResRange(BT bt, Index base, Index limit)
{
  AVERT_CRITICAL(BT, bt);   /* See .aver.critical */
  AVER_CRITICAL(base < limit);
  /* Can't check range of base or limit */

#define SINGLE_IS_RES_RANGE(i) \
  if (BTGet(bt, (i))) return FALSE
#define BITS_IS_RES_RANGE(i,base,limit) \
  if ((bt[(i)] & BTMask((base),(limit))) != (Word)0) return FALSE
#define WORD_IS_RES_RANGE(i) \
  if (bt[(i)] != (Word)0) return FALSE

  ACT_ON_RANGE(base, limit, SINGLE_IS_RES_RANGE,
               BITS_IS_RES_RANGE, WORD_IS_RES_RANGE);
  return TRUE;
}


/* BTIsSetRange -- test whether a range of bits is all set
 *
 * <design/bt#.fun.is-set-range>.
 */

Bool BTIsSetRange(BT bt, Index base, Index limit)
{
  AVERT(BT, bt);
  AVER(base < limit);
  /* Can't check range of base or limit */

#define SINGLE_IS_SET_RANGE(i) \
  if (!BTGet(bt, (i))) return FALSE
#define BITS_IS_SET_RANGE(i,base,limit) \
  BEGIN \
    Word bactMask = BTMask((base),(limit)); \
    if ((bt[(i)] & bactMask) != bactMask) \
      return FALSE; \
  END
#define WORD_IS_SET_RANGE(i) \
  if (bt[(i)] != ~(Word)0) return FALSE

  ACT_ON_RANGE(base, limit, SINGLE_IS_SET_RANGE,
               BITS_IS_SET_RANGE, WORD_IS_SET_RANGE);
  return TRUE;
}


/* BTResRange -- reset a range of bits in a BT
 *
 * <design/bt#.fun.res-range>
 */

void BTResRange(BT t, Index base, Index limit)
{
  AVERT(BT, t);
  AVER(base < limit);

#define SINGLE_RES_RANGE(i) \
  BTRes(t, (i))
#define BITS_RES_RANGE(i,base,limit) \
  t[(i)] &= ~(BTMask((base),(limit)))
#define WORD_RES_RANGE(i) t[(i)] = (Word)(0)

  ACT_ON_RANGE(base, limit, SINGLE_RES_RANGE,
               BITS_RES_RANGE, WORD_RES_RANGE);
}


/* BTFindSet -- find the lowest set bit in a range in a bit table.
 *
 * Sets foundReturn to false if the range is entirely reset;
 * in this case indexReturn is unset. Sets foundReturn to true
 * otherwise.
 *
 * Implemented as a macro for efficiency reasons.
 * The macro internally uses the label btFindSetLabel.
 * If the macro must be used more than once within a function
 * this label must be redefined to avoid a nameclash. E.g.
 *    #define btFindSetLabel uniqueLabel
 *    BTFindSet(...)
 *    #undef btFindSetLabel
 */

#define BTFindSet(foundReturn,indexReturn,bt,base,limit)\
  BEGIN \
    Bool *bfsFoundReturn = (foundReturn); \
    Index *bfsIndexReturn = (indexReturn); \
    BT bfsBt = (bt); \
    ACT_ON_RANGE((base), (limit), SINGLE_FIND_SET,  \
                 BITS_FIND_SET, WORD_FIND_SET); \
    *bfsFoundReturn = FALSE; \
btFindSetLabel:; \
  END

#define SINGLE_FIND_SET(i)  \
  if (BTGet(bfsBt, (i))) { \
    *bfsIndexReturn = (i); \
    *bfsFoundReturn = TRUE; \
    goto btFindSetLabel; \
  }
#define BITS_FIND_SET(wi,base,limit)  \
  BEGIN \
    Index bactWi = (wi); \
    ACTION_FIND_SET(bactWi, bfsBt[bactWi], (base), (limit)); \
  END
#define WORD_FIND_SET(wi) \
  BEGIN \
    Index wactWi = (wi); \
    ACTION_FIND_SET(wactWi, bfsBt[wactWi], 0, MPS_WORD_WIDTH); \
  END
#define ACTION_FIND_SET(wi,word,base,limit) \
  ACTION_FIND_SET_BIT((wi),(word),(base),(limit),btFindSetLabel)


/* ACTION_FIND_SET_BIT -- Find first set bit in a range
 *
 * Helper macro to find the low bit in a range of a word.
 * Works by first shifting the base of the range to the low
 * bits of the word. Then loops performing a binary chop
 * over the data looking to see if a bit is set in the lower
 * half. If not, it must be in the upper half which is then
 * shifted down. The loop completes after using a chop unit
 * of a single single bit.
 */

#define ACTION_FIND_SET_BIT(wi,word,base,limit,label) \
  BEGIN \
    /* no need to mask the low bits which are shifted */ \
    Index actionIndex = (base); \
    Word actionWord = ((word) & BTMaskHigh((limit))) >> actionIndex; \
    Count actionMaskWidth = (MPS_WORD_WIDTH >> 1); \
    Word actionMask = ~(Word)0 >> (MPS_WORD_WIDTH-actionMaskWidth); \
    if (actionWord != (Word)0) { \
      while (actionMaskWidth != (Count)0) { \
        if ((actionWord & actionMask) == (Word)0) { \
          actionIndex += actionMaskWidth; \
          actionWord >>= actionMaskWidth; \
        } \
        actionMaskWidth >>= 1; \
        actionMask >>= actionMaskWidth; \
      } \
      *bfsIndexReturn = ((wi) << MPS_WORD_SHIFT) | actionIndex; \
      *bfsFoundReturn = TRUE; \
      goto label; \
    } \
  END


/* BTFindRes -- find the lowest reset bit in a range in a bit table.
 *
 * Usage as for BTFindSet
 *
 * Internally uses the label btFindResLabel
 * which must be redefined to avoid a nameclash if the macro is
 * used twice in a function scope.
 */

#define BTFindRes(foundReturn,indexReturn,bt,base,limit)\
  BEGIN \
    Bool *bfsFoundReturn = (foundReturn); \
    Index *bfsIndexReturn = (indexReturn); \
    BT bfsBt = (bt); \
    ACT_ON_RANGE((base), (limit), SINGLE_FIND_RES,  \
                 BITS_FIND_RES, WORD_FIND_RES); \
    *bfsFoundReturn = FALSE; \
btFindResLabel:; \
  END

#define SINGLE_FIND_RES(i)  \
  if (!BTGet(bfsBt, (i))) { \
    *bfsIndexReturn = (i); \
    *bfsFoundReturn = TRUE; \
    goto btFindResLabel; \
  }
#define BITS_FIND_RES(wi,base,limit)  \
  BEGIN \
    Index bactWi = (wi); \
    ACTION_FIND_RES(bactWi,bfsBt[bactWi], (base), (limit)); \
  END
#define WORD_FIND_RES(wi) \
  BEGIN \
    Index wactWi = (wi); \
    ACTION_FIND_RES(wactWi, bfsBt[wactWi], 0, MPS_WORD_WIDTH); \
  END
#define ACTION_FIND_RES(wi,word,base,limit) \
  ACTION_FIND_SET_BIT((wi),~(word),(base),(limit),btFindResLabel)


/* BTFindSetHigh -- find the highest set bit in a range in a bit table.
 *
 * Usage as for BTFindSet
 *
 * Internally uses the label btFindSetHighLabel
 * which must be redefined to avoid a nameclash if the macro is
 * used twice in a function scope.
 */

#define BTFindSetHigh(foundReturn,indexReturn,bt,base,limit)\
  BEGIN \
    Bool *bfsFoundReturn = (foundReturn); \
    Index *bfsIndexReturn = (indexReturn); \
    BT bfsBt = (bt); \
    ACT_ON_RANGE_HIGH((base), (limit), SINGLE_FIND_SET_HIGH, \
                      BITS_FIND_SET_HIGH, WORD_FIND_SET_HIGH); \
    *bfsFoundReturn = FALSE; \
btFindSetHighLabel:; \
  END

#define SINGLE_FIND_SET_HIGH(i)  \
  if (BTGet(bfsBt, (i))) { \
    *bfsIndexReturn = (i); \
    *bfsFoundReturn = TRUE; \
    goto btFindSetHighLabel; \
  }
#define BITS_FIND_SET_HIGH(wi,base,limit) \
  BEGIN \
    Index bactWi = (wi); \
    ACTION_FIND_SET_HIGH(bactWi, bfsBt[bactWi], (base), (limit)); \
  END
#define WORD_FIND_SET_HIGH(wi) \
  BEGIN \
    Index wactWi = (wi); \
    ACTION_FIND_SET_HIGH(wactWi, (bfsBt[wactWi]), 0, MPS_WORD_WIDTH); \
  END
#define ACTION_FIND_SET_HIGH(wi,word,base,limit) \
  ACTION_FIND_SET_BIT_HIGH((wi),(word),(base),(limit),btFindSetHighLabel)


/* ACTION_FIND_SET_BIT_HIGH -- Find highest set bit in a range
 *
 * Helper macro to find the high bit in a range of a word.
 * Essentially a mirror image of ACTION_FIND_SET
 */

#define ACTION_FIND_SET_BIT_HIGH(wi,word,base,limit,label) \
  BEGIN \
    /* no need to mask the high bits which are shifted */ \
    Index actionShift = MPS_WORD_WIDTH - (limit);  \
    Index actionIndex = MPS_WORD_WIDTH - 1 - actionShift; \
    Word actionWord = ((word) & BTMaskLow((base))) << actionShift; \
    Count actionMaskWidth = (MPS_WORD_WIDTH >> 1); \
    Word actionMask = ~(Word)0 << (MPS_WORD_WIDTH-actionMaskWidth); \
    if (actionWord != (Word)0) { \
      while (actionMaskWidth != (Count)0) { \
        if ((actionWord & actionMask) == (Word)0) { \
          actionIndex -= actionMaskWidth; \
          actionWord <<= actionMaskWidth; \
        } \
        actionMaskWidth >>= 1; \
        actionMask <<= actionMaskWidth; \
      } \
      *bfsIndexReturn = ((wi) << MPS_WORD_SHIFT) | actionIndex; \
      *bfsFoundReturn = TRUE; \
      goto label; \
    } \
  END


/* BTFindResHigh -- find the highest reset bit in a range
 *
 * Usage as for BTFindSet
 *
 * Internally uses the label btFindSetHighLabel
 * which must be redefined to avoid a nameclash if the macro is
 * used twice in a function scope.
 */

#define BTFindResHigh(foundReturn,indexReturn,bt,base,limit)\
  BEGIN \
    Bool *bfsFoundReturn = (foundReturn); \
    Index *bfsIndexReturn = (indexReturn); \
    BT bfsBt = (bt); \
    ACT_ON_RANGE_HIGH((base), (limit), SINGLE_FIND_RES_HIGH, \
                      BITS_FIND_RES_HIGH, WORD_FIND_RES_HIGH); \
    *bfsFoundReturn = FALSE; \
btFindResHighLabel:; \
  END

#define SINGLE_FIND_RES_HIGH(i)  \
  if (!BTGet(bfsBt, (i))) { \
    *bfsIndexReturn = (i); \
    *bfsFoundReturn = TRUE; \
    goto btFindResHighLabel; \
  }
#define BITS_FIND_RES_HIGH(wi,base,limit) \
  BEGIN \
    Index bactWi = (wi); \
    ACTION_FIND_RES_HIGH(bactWi, bfsBt[bactWi], (base), (limit)); \
  END
#define WORD_FIND_RES_HIGH(wi) \
  BEGIN \
    Index wactWi = (wi); \
    ACTION_FIND_RES_HIGH(wactWi, (bfsBt[wactWi]), 0, MPS_WORD_WIDTH); \
  END
#define ACTION_FIND_RES_HIGH(wi,word,base,limit) \
  ACTION_FIND_SET_BIT_HIGH((wi),~(word),(base),(limit),btFindResHighLabel)


/* BTFindResRange -- find a reset range of bits in a bit table
 *
 * Starts searching at the low end of the search range.
 *
 * <design/bt#.fun.find-res-range>.
 */

static Bool BTFindResRange(Index *baseReturn, Index *limitReturn,
                           BT bt,
                           Index searchBase, Index searchLimit,
                           Count minLength, Count maxLength)
{
  Bool foundRes;         /* true if a reset bit is found */
  Index resBase;         /* base of a candidate reset range */
  Index unseenBase;      /* base of testing so far */
  Index minLimit;        /* limit of minimal acceptable range */
  Index resLimit;        /* limit of search for a candidate range */

  AVER(baseReturn != NULL);
  AVER(limitReturn != NULL);
  AVERT(BT, bt);
  AVER(searchBase < searchLimit);
  AVER(minLength > 0);
  AVER(minLength <= maxLength);
  AVER(maxLength <= searchLimit - searchBase);

  foundRes = FALSE;     /* don't know first reset bit */
  minLimit = 0;         /* avoid spurious compiler warning */
  resBase = searchBase; /* haven't seen anything yet */
  unseenBase = searchBase;  /* haven't seen anything yet */
  resLimit = searchLimit - minLength + 1;

  while (resBase < resLimit) {
    Index setIndex;  /* index of last set bit found */
    Bool foundSet = FALSE; /* true if a set bit is found */

    /* Find the first reset bit if it's not already known */
    if (!foundRes) {
      BTFindRes(&foundRes, &resBase, bt, unseenBase, resLimit);
      if (!foundRes) {
        /* failure */
        return FALSE;
      }
      unseenBase = resBase + 1;
      minLimit = resBase + minLength;
    }

    /* Look to see if there is any set bit in the minimum range */
    BTFindSetHigh(&foundSet, &setIndex, bt, unseenBase, minLimit);
    if (!foundSet) {
      /* Found minimum range. Extend it. */
      Index setBase;   /* base of search for set bit */
      Index setLimit;  /* limit search for set bit */
      foundSet = FALSE;
      setBase = minLimit;
      setLimit = resBase + maxLength;
      if (setLimit > searchLimit)
        setLimit = searchLimit;
      if (setLimit > setBase)
        BTFindSet(&foundSet, &setIndex, bt, setBase, setLimit);
      if (!foundSet)
        setIndex = setLimit;

      AVER(setIndex - resBase >= minLength);
      AVER(setIndex - resBase <= maxLength);
      *baseReturn = resBase;
      *limitReturn = setIndex;
      return TRUE;

    } else {
      /* Range was too small. Try again */
      unseenBase = minLimit;
      resBase = setIndex + 1;
      if (resBase != minLimit) {
        /* Already found the start of next candidate range */
        minLimit = resBase + minLength;
        /* minLimit might just have gone out of bounds, but in that
         * case resBase >= resLimit and so the loop will exit. */
        AVER(minLimit <= searchLimit || resBase >= resLimit);
      } else {
        foundRes = FALSE;
      }
    }
  }

  /* failure */
  return FALSE;
}


/* BTFindResRangeHigh -- find a reset range of bits in a bit table
 *
 * Starts searching at the high end of the search range.
 *
 * <design/bt#.fun.find-res-range>.
 */

static Bool BTFindResRangeHigh(Index *baseReturn, Index *limitReturn,
                               BT bt,
                               Index searchBase, Index searchLimit,
                               Count minLength,
                               Count maxLength)
{
  Bool foundRes;         /* true if a reset bit is found */
  Index resLimit;        /* limit of a candidate reset range */
  Index resIndex;        /* index of highest reset bit found */
  Index unseenLimit;     /* limit of testing so far */
  Index minBase;         /* base of minimal acceptable range */
  Index resBase;         /* base of search for a candidate range */

  AVER(baseReturn != NULL);
  AVER(limitReturn != NULL);
  AVERT(BT, bt);
  AVER(searchBase < searchLimit);
  AVER(minLength > 0);
  AVER(minLength <= maxLength);
  AVER(maxLength <= searchLimit - searchBase);

  foundRes = FALSE;     /* don't know first reset bit */
  minBase = 0;          /* avoid spurious compiler warning */
  resLimit = searchLimit;    /* haven't seen anything yet */
  unseenLimit = searchLimit; /* haven't seen anything yet */
  resBase = searchBase + minLength -1;

  while (resLimit > resBase) {
    Index setIndex;  /* index of first set bit found */
    Bool foundSet = FALSE; /* true if a set bit is found */

    /* Find the first reset bit if it's not already known */
    if (!foundRes) {
      /* Look for the limit of a range */
      BTFindResHigh(&foundRes, &resIndex, bt, resBase, unseenLimit);
      if (!foundRes) {
        /* failure */
        return FALSE;
      }
      resLimit = resIndex + 1;
      unseenLimit = resIndex;
      minBase = resLimit - minLength;
    }

    /* Look to see if there is any set bit in the minimum range */
    BTFindSet(&foundSet, &setIndex, bt, minBase, unseenLimit);
    if (!foundSet) {
      /* Found minimum range. Extend it. */
      Index setBase;   /* base of search for set bit */
      Index setLimit;  /* limit search for set bit */
      Index baseIndex; /* base of reset range found */
      foundSet = FALSE;
      setLimit = minBase;
      if ((searchBase + maxLength) > resLimit)
        setBase = searchBase;
      else
        setBase  = resLimit - maxLength;
      if (setLimit > setBase)
        BTFindSetHigh(&foundSet, &setIndex, bt, setBase, setLimit);
      if (foundSet)
        baseIndex = setIndex+1;
      else
        baseIndex = setBase;

      AVER(resLimit - baseIndex >= minLength);
      AVER(resLimit - baseIndex <= maxLength);
      *baseReturn = baseIndex;
      *limitReturn = resLimit;
      return TRUE;

    } else {
      /* Range was too small. Try again */
      unseenLimit = minBase;
      resLimit = setIndex;
      if (resLimit != minBase) {
        /* Already found the start of next candidate range. This wraps
         * round if minLength > resLimit (all the variables are
         * unsigned so this behaviour is defined), but that means that
         * resLimit <= resBase and so the loop will exit. */
        AVER(resLimit >= minLength || resLimit <= resBase);
        minBase = resLimit - minLength;
      } else {
        foundRes = FALSE;
      }
    }
  }

  /* failure */
  return FALSE;
}


/* BTFindLongResRange -- find long range of reset bits in a bit table
 *
 * <design/bt#.fun.find-long-res-range>.
 */

Bool BTFindLongResRange(Index *baseReturn, Index *limitReturn,
                        BT bt,
                        Index searchBase, Index searchLimit,
                        Count length)
{
  /* All parameters are checked by BTFindResRange. */
  return BTFindResRange(baseReturn, limitReturn,
                        bt,
                        searchBase, searchLimit,
                        length, searchLimit - searchBase);
}


/* BTFindLongResRangeHigh -- find long range of reset bits in a bit table
 *
 * <design/bt#.fun.find-long-res-range-high>.
 */

Bool BTFindLongResRangeHigh(Index *baseReturn, Index *limitReturn,
                            BT bt,
                            Index searchBase, Index searchLimit,
                            Count length)
{
  /* All parameters are checked by BTFindResRangeHigh. */
  return BTFindResRangeHigh(baseReturn, limitReturn,
                            bt,
                            searchBase, searchLimit,
                            length, searchLimit - searchBase);
}


/* BTFindShortResRange -- find short range of reset bits in a bit table
 *
 * <design/bt#.fun.find-short-res-range>.
 */

Bool BTFindShortResRange(Index *baseReturn, Index *limitReturn,
                         BT bt,
                         Index searchBase, Index searchLimit,
                         Count length)
{
  /* All parameters are checked by BTFindResRange. */
  return BTFindResRange(baseReturn, limitReturn,
                        bt,
                        searchBase, searchLimit,
                        length, length);
}

/* BTFindShortResRangeHigh -- find short range of reset bits in a bit table
 *
 * Starts looking from the top of the search range.
 *
 * <design/bt#.fun.find-short-res-range-high>.
 */

Bool BTFindShortResRangeHigh(Index *baseReturn, Index *limitReturn,
                             BT bt,
                             Index searchBase, Index searchLimit,
                             Count length)
{
  /* All parameters are checked by BTFindResRangeHigh. */
  return BTFindResRangeHigh(baseReturn, limitReturn,
                            bt,
                            searchBase, searchLimit,
                            length, length);
}


/* BTRangesSame -- check that a range of bits in two BTs are the same.
 *
 * <design/bt#.if.ranges-same>
 */

Bool BTRangesSame(BT comparand, BT comparator, Index base, Index limit)
{
  AVERT(BT, comparand);
  AVERT(BT, comparator);
  AVER(base < limit);

#define SINGLE_RANGES_SAME(i) \
  if (BTGet(comparand, (i)) != BTGet(comparator, (i))) \
      return FALSE
#define BITS_RANGES_SAME(i,base,limit) \
  BEGIN \
    Index bactI = (i); \
    Word bactMask = BTMask((base),(limit)); \
    if ((comparand[bactI] & (bactMask)) != \
       (comparator[bactI] & (bactMask))) \
      return FALSE; \
  END
#define WORD_RANGES_SAME(i) \
  BEGIN \
    Index wactI = (i); \
    if ((comparand[wactI]) != (comparator[wactI])) \
      return FALSE; \
  END

  ACT_ON_RANGE(base, limit, SINGLE_RANGES_SAME,
               BITS_RANGES_SAME, WORD_RANGES_SAME);
  return TRUE;
}


/* BTCopyInvertRange -- copy a range of bits from one BT to another,
 * inverting them as you go.
 *
 * <design/bt#.if.copy-invert-range>
 */

void BTCopyInvertRange(BT fromBT, BT toBT, Index base, Index limit)
{
  AVERT(BT, fromBT);
  AVERT(BT, toBT);
  AVER(fromBT != toBT);
  AVER(base < limit);

#define SINGLE_COPY_INVERT_RANGE(i) \
  if (BTGet(fromBT, (i))) \
    BTRes(toBT, (i)); \
  else \
    BTSet(toBT, (i))
#define BITS_COPY_INVERT_RANGE(i,base,limit) \
  BEGIN \
    Index bactI = (i); \
    Word bactMask = BTMask((base),(limit)); \
    toBT[bactI] = \
      (toBT[bactI] & ~bactMask) | (~fromBT[bactI] & bactMask); \
  END
#define WORD_COPY_INVERT_RANGE(i) \
  BEGIN \
    Index wactI = (i); \
    toBT[wactI] = ~fromBT[wactI]; \
  END

  ACT_ON_RANGE(base, limit, SINGLE_COPY_INVERT_RANGE,
               BITS_COPY_INVERT_RANGE, WORD_COPY_INVERT_RANGE);
}


/* BTCopyRange -- copy a range of bits from one BT to another
 *
 * <design/bt#.if.copy-range>
 */

void BTCopyRange(BT fromBT, BT toBT, Index base, Index limit)
{
  AVERT(BT, fromBT);
  AVERT(BT, toBT);
  AVER(fromBT != toBT);
  AVER(base < limit);

#define SINGLE_COPY_RANGE(i) \
  if (BTGet(fromBT, (i))) \
    BTSet(toBT, (i)); \
  else \
    BTRes(toBT, (i))
#define BITS_COPY_RANGE(i,base,limit) \
  BEGIN \
    Index bactI = (i); \
    Word bactMask = BTMask((base),(limit)); \
    toBT[bactI] = \
      (toBT[bactI] & ~bactMask) | (fromBT[bactI] & bactMask); \
  END
#define WORD_COPY_RANGE(i) \
  BEGIN \
    Index wactI = (i); \
    toBT[wactI] = fromBT[wactI]; \
  END

  ACT_ON_RANGE(base, limit, SINGLE_COPY_RANGE,
               BITS_COPY_RANGE, WORD_COPY_RANGE);
}


/* BTCopyOffsetRange -- copy a range of bits from one BT to an
 * offset range in another BT
 *
 * .slow: Can't always use ACT_ON_RANGE because word alignment
 * may differ for each range. We could try to be smart about
 * detecting similar alignment - but we don't.
 *
 * <design/bt#.if.copy-offset-range>
 */

void BTCopyOffsetRange(BT fromBT, BT toBT,
                       Index fromBase, Index fromLimit,
                       Index toBase, Index toLimit)
{
  Index fromBit, toBit;

  AVERT(BT, fromBT);
  AVERT(BT, toBT);
  AVER(fromBT != toBT);
  AVER(fromBase < fromLimit);
  AVER(toBase < toLimit);
  AVER((fromLimit - fromBase) == (toLimit - toBase));

  for (ITER_PARALLEL(fromBit = fromBase, toBit = toBase);
       fromBit < fromLimit;
       ITER_PARALLEL(++fromBit, ++toBit))
  {
    if (BTGet(fromBT, fromBit))
      BTSet(toBT, toBit);
    else
      BTRes(toBT, toBit);
  }
}


/* BTCountResRange -- count number of reset bits in a range */

Count BTCountResRange(BT bt, Index base, Index limit)
{
  Count c = 0;
  Index bit;

  AVERT(BT, bt);
  AVER(base < limit);

  for (bit = base; bit < limit; ++bit)
    if (!BTGet(bt, bit))
      ++c;
  return c;
}


/* C. COPYRIGHT AND LICENSE
 *
 * Copyright (C) 2001-2020 Ravenbrook Limited <https://www.ravenbrook.com/>.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are
 * met:
 *
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 *
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the
 *    distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS
 * IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
 * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A
 * PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
 * HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */