PostgreSQL Source Code git master
integerset.c File Reference
#include "postgres.h"
#include "lib/integerset.h"
#include "utils/memutils.h"
Include dependency graph for integerset.c:

Go to the source code of this file.

Data Structures

struct  intset_node
 
struct  intset_internal_node
 
struct  leaf_item
 
struct  intset_leaf_node
 
struct  IntegerSet
 
struct  simple8b_mode
 

Macros

#define SIMPLE8B_MAX_VALUES_PER_CODEWORD   240
 
#define MAX_INTERNAL_ITEMS   64
 
#define MAX_LEAF_ITEMS   64
 
#define MAX_TREE_LEVELS   11
 
#define MAX_VALUES_PER_LEAF_ITEM   (1 + SIMPLE8B_MAX_VALUES_PER_CODEWORD)
 
#define MAX_BUFFERED_VALUES   (MAX_VALUES_PER_LEAF_ITEM * 2)
 
#define EMPTY_CODEWORD   UINT64CONST(0x0FFFFFFFFFFFFFFF)
 

Typedefs

typedef struct intset_node intset_node
 
typedef struct intset_leaf_node intset_leaf_node
 
typedef struct intset_internal_node intset_internal_node
 

Functions

static void intset_update_upper (IntegerSet *intset, int level, intset_node *child, uint64 child_key)
 
static void intset_flush_buffered_values (IntegerSet *intset)
 
static int intset_binsrch_uint64 (uint64 item, uint64 *arr, int arr_elems, bool nextkey)
 
static int intset_binsrch_leaf (uint64 item, leaf_item *arr, int arr_elems, bool nextkey)
 
static uint64 simple8b_encode (const uint64 *ints, int *num_encoded, uint64 base)
 
static int simple8b_decode (uint64 codeword, uint64 *decoded, uint64 base)
 
static bool simple8b_contains (uint64 codeword, uint64 key, uint64 base)
 
IntegerSetintset_create (void)
 
static intset_internal_nodeintset_new_internal_node (IntegerSet *intset)
 
static intset_leaf_nodeintset_new_leaf_node (IntegerSet *intset)
 
uint64 intset_num_entries (IntegerSet *intset)
 
uint64 intset_memory_usage (IntegerSet *intset)
 
void intset_add_member (IntegerSet *intset, uint64 x)
 
bool intset_is_member (IntegerSet *intset, uint64 x)
 
void intset_begin_iterate (IntegerSet *intset)
 
bool intset_iterate_next (IntegerSet *intset, uint64 *next)
 

Variables

static const struct simple8b_mode simple8b_modes [17]
 

Macro Definition Documentation

◆ EMPTY_CODEWORD

#define EMPTY_CODEWORD   UINT64CONST(0x0FFFFFFFFFFFFFFF)

Definition at line 856 of file integerset.c.

◆ MAX_BUFFERED_VALUES

#define MAX_BUFFERED_VALUES   (MAX_VALUES_PER_LEAF_ITEM * 2)

Definition at line 186 of file integerset.c.

◆ MAX_INTERNAL_ITEMS

#define MAX_INTERNAL_ITEMS   64

Definition at line 94 of file integerset.c.

◆ MAX_LEAF_ITEMS

#define MAX_LEAF_ITEMS   64

Definition at line 95 of file integerset.c.

◆ MAX_TREE_LEVELS

#define MAX_TREE_LEVELS   11

Definition at line 109 of file integerset.c.

◆ MAX_VALUES_PER_LEAF_ITEM

#define MAX_VALUES_PER_LEAF_ITEM   (1 + SIMPLE8B_MAX_VALUES_PER_CODEWORD)

Definition at line 166 of file integerset.c.

◆ SIMPLE8B_MAX_VALUES_PER_CODEWORD

#define SIMPLE8B_MAX_VALUES_PER_CODEWORD   240

Definition at line 83 of file integerset.c.

Typedef Documentation

◆ intset_internal_node

Definition at line 135 of file integerset.c.

◆ intset_leaf_node

Definition at line 134 of file integerset.c.

◆ intset_node

typedef struct intset_node intset_node

Definition at line 133 of file integerset.c.

Function Documentation

◆ intset_add_member()

void intset_add_member ( IntegerSet intset,
uint64  x 
)

Definition at line 369 of file integerset.c.

370{
371 if (intset->iter_active)
372 elog(ERROR, "cannot add new values to integer set while iteration is in progress");
373
374 if (x <= intset->highest_value && intset->num_entries > 0)
375 elog(ERROR, "cannot add value to integer set out of order");
376
377 if (intset->num_buffered_values >= MAX_BUFFERED_VALUES)
378 {
379 /* Time to flush our buffer */
381 Assert(intset->num_buffered_values < MAX_BUFFERED_VALUES);
382 }
383
384 /* Add it to the buffer of newly-added values */
385 intset->buffered_values[intset->num_buffered_values] = x;
386 intset->num_buffered_values++;
387 intset->num_entries++;
388 intset->highest_value = x;
389}
Datum intset(PG_FUNCTION_ARGS)
Definition: _int_op.c:179
#define Assert(condition)
Definition: c.h:815
#define ERROR
Definition: elog.h:39
#define elog(elevel,...)
Definition: elog.h:225
#define MAX_BUFFERED_VALUES
Definition: integerset.c:186
static void intset_flush_buffered_values(IntegerSet *intset)
Definition: integerset.c:395
int x
Definition: isn.c:70

References Assert, elog, ERROR, intset(), intset_flush_buffered_values(), MAX_BUFFERED_VALUES, and x.

Referenced by gistvacuumpage(), test_huge_distances(), test_pattern(), test_single_value(), and test_single_value_and_filler().

◆ intset_begin_iterate()

void intset_begin_iterate ( IntegerSet intset)

Definition at line 623 of file integerset.c.

624{
625 /* Note that we allow an iteration to be abandoned midway */
626 intset->iter_active = true;
627 intset->iter_node = intset->leftmost_leaf;
628 intset->iter_itemno = 0;
629 intset->iter_valueno = 0;
630 intset->iter_num_values = 0;
631 intset->iter_values = intset->iter_values_buf;
632}

References intset().

Referenced by gistvacuum_delete_empty_pages(), test_empty(), test_huge_distances(), test_pattern(), test_single_value(), and test_single_value_and_filler().

◆ intset_binsrch_leaf()

static int intset_binsrch_leaf ( uint64  item,
leaf_item arr,
int  arr_elems,
bool  nextkey 
)
static

Definition at line 746 of file integerset.c.

747{
748 int low,
749 high,
750 mid;
751
752 low = 0;
753 high = arr_elems;
754 while (high > low)
755 {
756 mid = low + (high - low) / 2;
757
758 if (nextkey)
759 {
760 if (item >= arr[mid].first)
761 low = mid + 1;
762 else
763 high = mid;
764 }
765 else
766 {
767 if (item > arr[mid].first)
768 low = mid + 1;
769 else
770 high = mid;
771 }
772 }
773
774 return low;
775}

Referenced by intset_is_member().

◆ intset_binsrch_uint64()

static int intset_binsrch_uint64 ( uint64  item,
uint64 arr,
int  arr_elems,
bool  nextkey 
)
static

Definition at line 713 of file integerset.c.

714{
715 int low,
716 high,
717 mid;
718
719 low = 0;
720 high = arr_elems;
721 while (high > low)
722 {
723 mid = low + (high - low) / 2;
724
725 if (nextkey)
726 {
727 if (item >= arr[mid])
728 low = mid + 1;
729 else
730 high = mid;
731 }
732 else
733 {
734 if (item > arr[mid])
735 low = mid + 1;
736 else
737 high = mid;
738 }
739 }
740
741 return low;
742}

Referenced by intset_is_member().

◆ intset_create()

IntegerSet * intset_create ( void  )

Definition at line 283 of file integerset.c.

284{
286
287 intset = (IntegerSet *) palloc(sizeof(IntegerSet));
288 intset->context = CurrentMemoryContext;
289 intset->mem_used = GetMemoryChunkSpace(intset);
290
291 intset->num_entries = 0;
292 intset->highest_value = 0;
293
294 intset->num_levels = 0;
295 intset->root = NULL;
296 memset(intset->rightmost_nodes, 0, sizeof(intset->rightmost_nodes));
297 intset->leftmost_leaf = NULL;
298
299 intset->num_buffered_values = 0;
300
301 intset->iter_active = false;
302 intset->iter_node = NULL;
303 intset->iter_itemno = 0;
304 intset->iter_valueno = 0;
305 intset->iter_num_values = 0;
306 intset->iter_values = NULL;
307
308 return intset;
309}
Size GetMemoryChunkSpace(void *pointer)
Definition: mcxt.c:721
void * palloc(Size size)
Definition: mcxt.c:1317
MemoryContext CurrentMemoryContext
Definition: mcxt.c:143

References CurrentMemoryContext, GetMemoryChunkSpace(), intset(), and palloc().

Referenced by gistvacuumscan(), test_empty(), test_huge_distances(), test_pattern(), test_single_value(), and test_single_value_and_filler().

◆ intset_flush_buffered_values()

static void intset_flush_buffered_values ( IntegerSet intset)
static

Definition at line 395 of file integerset.c.

396{
397 uint64 *values = intset->buffered_values;
398 uint64 num_values = intset->num_buffered_values;
399 int num_packed = 0;
400 intset_leaf_node *leaf;
401
402 leaf = (intset_leaf_node *) intset->rightmost_nodes[0];
403
404 /*
405 * If the tree is completely empty, create the first leaf page, which is
406 * also the root.
407 */
408 if (leaf == NULL)
409 {
410 /*
411 * This is the very first item in the set.
412 *
413 * Allocate root node. It's also a leaf.
414 */
416
417 intset->root = (intset_node *) leaf;
418 intset->leftmost_leaf = leaf;
419 intset->rightmost_nodes[0] = (intset_node *) leaf;
420 intset->num_levels = 1;
421 }
422
423 /*
424 * If there are less than MAX_VALUES_PER_LEAF_ITEM values in the buffer,
425 * stop. In most cases, we cannot encode that many values in a single
426 * value, but this way, the encoder doesn't have to worry about running
427 * out of input.
428 */
429 while (num_values - num_packed >= MAX_VALUES_PER_LEAF_ITEM)
430 {
431 leaf_item item;
432 int num_encoded;
433
434 /*
435 * Construct the next leaf item, packing as many buffered values as
436 * possible.
437 */
438 item.first = values[num_packed];
439 item.codeword = simple8b_encode(&values[num_packed + 1],
440 &num_encoded,
441 item.first);
442
443 /*
444 * Add the item to the node, allocating a new node if the old one is
445 * full.
446 */
447 if (leaf->num_items >= MAX_LEAF_ITEMS)
448 {
449 /* Allocate new leaf and link it to the tree */
450 intset_leaf_node *old_leaf = leaf;
451
453 old_leaf->next = leaf;
454 intset->rightmost_nodes[0] = (intset_node *) leaf;
455 intset_update_upper(intset, 1, (intset_node *) leaf, item.first);
456 }
457 leaf->items[leaf->num_items++] = item;
458
459 num_packed += 1 + num_encoded;
460 }
461
462 /*
463 * Move any remaining buffered values to the beginning of the array.
464 */
465 if (num_packed < intset->num_buffered_values)
466 {
467 memmove(&intset->buffered_values[0],
468 &intset->buffered_values[num_packed],
469 (intset->num_buffered_values - num_packed) * sizeof(uint64));
470 }
471 intset->num_buffered_values -= num_packed;
472}
static Datum values[MAXATTR]
Definition: bootstrap.c:151
uint64_t uint64
Definition: c.h:489
#define MAX_VALUES_PER_LEAF_ITEM
Definition: integerset.c:166
static void intset_update_upper(IntegerSet *intset, int level, intset_node *child, uint64 child_key)
Definition: integerset.c:480
static uint64 simple8b_encode(const uint64 *ints, int *num_encoded, uint64 base)
Definition: integerset.c:872
#define MAX_LEAF_ITEMS
Definition: integerset.c:95
static intset_leaf_node * intset_new_leaf_node(IntegerSet *intset)
Definition: integerset.c:330
if(TABLE==NULL||TABLE_index==NULL)
Definition: isn.c:76
leaf_item items[MAX_LEAF_ITEMS]
Definition: integerset.c:176
intset_leaf_node * next
Definition: integerset.c:174
uint64 codeword
Definition: integerset.c:163
uint64 first
Definition: integerset.c:162

References leaf_item::codeword, leaf_item::first, if(), intset(), intset_new_leaf_node(), intset_update_upper(), intset_leaf_node::items, MAX_LEAF_ITEMS, MAX_VALUES_PER_LEAF_ITEM, intset_leaf_node::next, intset_leaf_node::num_items, simple8b_encode(), and values.

Referenced by intset_add_member().

◆ intset_is_member()

bool intset_is_member ( IntegerSet intset,
uint64  x 
)

Definition at line 553 of file integerset.c.

554{
555 intset_node *node;
556 intset_leaf_node *leaf;
557 int level;
558 int itemno;
559 leaf_item *item;
560
561 /*
562 * The value might be in the buffer of newly-added values.
563 */
564 if (intset->num_buffered_values > 0 && x >= intset->buffered_values[0])
565 {
566 itemno = intset_binsrch_uint64(x,
567 intset->buffered_values,
568 intset->num_buffered_values,
569 false);
570 if (itemno >= intset->num_buffered_values)
571 return false;
572 else
573 return (intset->buffered_values[itemno] == x);
574 }
575
576 /*
577 * Start from the root, and walk down the B-tree to find the right leaf
578 * node.
579 */
580 if (!intset->root)
581 return false;
582 node = intset->root;
583 for (level = intset->num_levels - 1; level > 0; level--)
584 {
586
587 Assert(node->level == level);
588
589 itemno = intset_binsrch_uint64(x, n->values, n->num_items, true);
590 if (itemno == 0)
591 return false;
592 node = n->downlinks[itemno - 1];
593 }
594 Assert(node->level == 0);
595 leaf = (intset_leaf_node *) node;
596
597 /*
598 * Binary search to find the right item on the leaf page
599 */
600 itemno = intset_binsrch_leaf(x, leaf->items, leaf->num_items, true);
601 if (itemno == 0)
602 return false;
603 item = &leaf->items[itemno - 1];
604
605 /* Is this a match to the first value on the item? */
606 if (item->first == x)
607 return true;
608 Assert(x > item->first);
609
610 /* Is it in the packed codeword? */
611 if (simple8b_contains(item->codeword, x, item->first))
612 return true;
613
614 return false;
615}
static int intset_binsrch_uint64(uint64 item, uint64 *arr, int arr_elems, bool nextkey)
Definition: integerset.c:713
static int intset_binsrch_leaf(uint64 item, leaf_item *arr, int arr_elems, bool nextkey)
Definition: integerset.c:746
static bool simple8b_contains(uint64 codeword, uint64 key, uint64 base)
Definition: integerset.c:1003
intset_node * downlinks[MAX_INTERNAL_ITEMS]
Definition: integerset.c:156
uint64 values[MAX_INTERNAL_ITEMS]
Definition: integerset.c:155
uint16 level
Definition: integerset.c:140

References Assert, leaf_item::codeword, intset_internal_node::downlinks, leaf_item::first, intset(), intset_binsrch_leaf(), intset_binsrch_uint64(), intset_leaf_node::items, intset_node::level, intset_internal_node::num_items, intset_leaf_node::num_items, simple8b_contains(), intset_internal_node::values, and x.

Referenced by check_with_filler(), gistvacuum_delete_empty_pages(), test_empty(), test_huge_distances(), test_pattern(), and test_single_value().

◆ intset_iterate_next()

bool intset_iterate_next ( IntegerSet intset,
uint64 next 
)

Definition at line 642 of file integerset.c.

643{
644 Assert(intset->iter_active);
645 for (;;)
646 {
647 /* Return next iter_values[] entry if any */
648 if (intset->iter_valueno < intset->iter_num_values)
649 {
650 *next = intset->iter_values[intset->iter_valueno++];
651 return true;
652 }
653
654 /* Decode next item in current leaf node, if any */
655 if (intset->iter_node &&
656 intset->iter_itemno < intset->iter_node->num_items)
657 {
658 leaf_item *item;
659 int num_decoded;
660
661 item = &intset->iter_node->items[intset->iter_itemno++];
662
663 intset->iter_values_buf[0] = item->first;
664 num_decoded = simple8b_decode(item->codeword,
665 &intset->iter_values_buf[1],
666 item->first);
667 intset->iter_num_values = num_decoded + 1;
668 intset->iter_valueno = 0;
669 continue;
670 }
671
672 /* No more items on this leaf, step to next node */
673 if (intset->iter_node)
674 {
675 intset->iter_node = intset->iter_node->next;
676 intset->iter_itemno = 0;
677 continue;
678 }
679
680 /*
681 * We have reached the end of the B-tree. But we might still have
682 * some integers in the buffer of newly-added values.
683 */
684 if (intset->iter_values == (const uint64 *) intset->iter_values_buf)
685 {
686 intset->iter_values = intset->buffered_values;
687 intset->iter_num_values = intset->num_buffered_values;
688 intset->iter_valueno = 0;
689 continue;
690 }
691
692 break;
693 }
694
695 /* No more results. */
696 intset->iter_active = false;
697 *next = 0; /* prevent uninitialized-variable warnings */
698 return false;
699}
static int32 next
Definition: blutils.c:221
static int simple8b_decode(uint64 codeword, uint64 *decoded, uint64 base)
Definition: integerset.c:974

References Assert, leaf_item::codeword, leaf_item::first, intset(), next, and simple8b_decode().

Referenced by gistvacuum_delete_empty_pages(), test_empty(), test_huge_distances(), test_pattern(), test_single_value(), and test_single_value_and_filler().

◆ intset_memory_usage()

uint64 intset_memory_usage ( IntegerSet intset)

Definition at line 358 of file integerset.c.

359{
360 return intset->mem_used;
361}

References intset().

Referenced by test_pattern(), and test_single_value_and_filler().

◆ intset_new_internal_node()

static intset_internal_node * intset_new_internal_node ( IntegerSet intset)
static

Definition at line 315 of file integerset.c.

316{
318
320 sizeof(intset_internal_node));
321 intset->mem_used += GetMemoryChunkSpace(n);
322
323 n->level = 0; /* caller must set */
324 n->num_items = 0;
325
326 return n;
327}
void * MemoryContextAlloc(MemoryContext context, Size size)
Definition: mcxt.c:1181

References GetMemoryChunkSpace(), intset(), intset_internal_node::level, MemoryContextAlloc(), and intset_internal_node::num_items.

Referenced by intset_update_upper().

◆ intset_new_leaf_node()

static intset_leaf_node * intset_new_leaf_node ( IntegerSet intset)
static

Definition at line 330 of file integerset.c.

331{
333
335 sizeof(intset_leaf_node));
336 intset->mem_used += GetMemoryChunkSpace(n);
337
338 n->level = 0;
339 n->num_items = 0;
340 n->next = NULL;
341
342 return n;
343}

References GetMemoryChunkSpace(), intset(), intset_leaf_node::level, MemoryContextAlloc(), intset_leaf_node::next, and intset_leaf_node::num_items.

Referenced by intset_flush_buffered_values().

◆ intset_num_entries()

uint64 intset_num_entries ( IntegerSet intset)

Definition at line 349 of file integerset.c.

350{
351 return intset->num_entries;
352}

References intset().

Referenced by gistvacuum_delete_empty_pages(), test_pattern(), test_single_value(), and test_single_value_and_filler().

◆ intset_update_upper()

static void intset_update_upper ( IntegerSet intset,
int  level,
intset_node child,
uint64  child_key 
)
static

Definition at line 480 of file integerset.c.

482{
483 intset_internal_node *parent;
484
485 Assert(level > 0);
486
487 /*
488 * Create a new root node, if necessary.
489 */
490 if (level >= intset->num_levels)
491 {
492 intset_node *oldroot = intset->root;
493 uint64 downlink_key;
494
495 /* MAX_TREE_LEVELS should be more than enough, this shouldn't happen */
496 if (intset->num_levels == MAX_TREE_LEVELS)
497 elog(ERROR, "could not expand integer set, maximum number of levels reached");
498 intset->num_levels++;
499
500 /*
501 * Get the first value on the old root page, to be used as the
502 * downlink.
503 */
504 if (intset->root->level == 0)
505 downlink_key = ((intset_leaf_node *) oldroot)->items[0].first;
506 else
507 downlink_key = ((intset_internal_node *) oldroot)->values[0];
508
510 parent->level = level;
511 parent->values[0] = downlink_key;
512 parent->downlinks[0] = oldroot;
513 parent->num_items = 1;
514
515 intset->root = (intset_node *) parent;
516 intset->rightmost_nodes[level] = (intset_node *) parent;
517 }
518
519 /*
520 * Place the downlink on the parent page.
521 */
522 parent = (intset_internal_node *) intset->rightmost_nodes[level];
523
525 {
526 parent->values[parent->num_items] = child_key;
527 parent->downlinks[parent->num_items] = child;
528 parent->num_items++;
529 }
530 else
531 {
532 /*
533 * Doesn't fit. Allocate new parent, with the downlink as the first
534 * item on it, and recursively insert the downlink to the new parent
535 * to the grandparent.
536 */
538 parent->level = level;
539 parent->values[0] = child_key;
540 parent->downlinks[0] = child;
541 parent->num_items = 1;
542
543 intset->rightmost_nodes[level] = (intset_node *) parent;
544
545 intset_update_upper(intset, level + 1, (intset_node *) parent, child_key);
546 }
547}
#define MAX_INTERNAL_ITEMS
Definition: integerset.c:94
#define MAX_TREE_LEVELS
Definition: integerset.c:109
static intset_internal_node * intset_new_internal_node(IntegerSet *intset)
Definition: integerset.c:315

References Assert, intset_internal_node::downlinks, elog, ERROR, if(), intset(), intset_new_internal_node(), intset_update_upper(), intset_internal_node::level, MAX_INTERNAL_ITEMS, MAX_TREE_LEVELS, intset_internal_node::num_items, and intset_internal_node::values.

Referenced by intset_flush_buffered_values(), and intset_update_upper().

◆ simple8b_contains()

static bool simple8b_contains ( uint64  codeword,
uint64  key,
uint64  base 
)
static

Definition at line 1003 of file integerset.c.

1004{
1005 int selector = (codeword >> 60);
1006 int nints = simple8b_modes[selector].num_ints;
1007 int bits = simple8b_modes[selector].bits_per_int;
1008
1009 if (codeword == EMPTY_CODEWORD)
1010 return false;
1011
1012 if (bits == 0)
1013 {
1014 /* Special handling for 0-bit cases. */
1015 return (key - base) <= nints;
1016 }
1017 else
1018 {
1019 uint64 mask = (UINT64CONST(1) << bits) - 1;
1020 uint64 curr_value;
1021
1022 curr_value = base;
1023 for (int i = 0; i < nints; i++)
1024 {
1025 uint64 diff = codeword & mask;
1026
1027 curr_value += 1 + diff;
1028
1029 if (curr_value >= key)
1030 {
1031 if (curr_value == key)
1032 return true;
1033 else
1034 return false;
1035 }
1036
1037 codeword >>= bits;
1038 }
1039 }
1040 return false;
1041}
#define UINT64CONST(x)
Definition: c.h:503
#define EMPTY_CODEWORD
Definition: integerset.c:856
static const struct simple8b_mode simple8b_modes[17]
int i
Definition: isn.c:72
uint8 bits_per_int
Definition: integerset.c:822
uint8 num_ints
Definition: integerset.c:823

References simple8b_mode::bits_per_int, EMPTY_CODEWORD, i, sort-test::key, simple8b_mode::num_ints, simple8b_modes, and UINT64CONST.

Referenced by intset_is_member().

◆ simple8b_decode()

static int simple8b_decode ( uint64  codeword,
uint64 decoded,
uint64  base 
)
static

Definition at line 974 of file integerset.c.

975{
976 int selector = (codeword >> 60);
977 int nints = simple8b_modes[selector].num_ints;
978 int bits = simple8b_modes[selector].bits_per_int;
979 uint64 mask = (UINT64CONST(1) << bits) - 1;
980 uint64 curr_value;
981
982 if (codeword == EMPTY_CODEWORD)
983 return 0;
984
985 curr_value = base;
986 for (int i = 0; i < nints; i++)
987 {
988 uint64 diff = codeword & mask;
989
990 curr_value += 1 + diff;
991 decoded[i] = curr_value;
992 codeword >>= bits;
993 }
994 return nints;
995}

References simple8b_mode::bits_per_int, EMPTY_CODEWORD, i, simple8b_mode::num_ints, simple8b_modes, and UINT64CONST.

Referenced by intset_iterate_next().

◆ simple8b_encode()

static uint64 simple8b_encode ( const uint64 ints,
int *  num_encoded,
uint64  base 
)
static

Definition at line 872 of file integerset.c.

873{
874 int selector;
875 int nints;
876 int bits;
877 uint64 diff;
878 uint64 last_val;
879 uint64 codeword;
880 int i;
881
882 Assert(ints[0] > base);
883
884 /*
885 * Select the "mode" to use for this codeword.
886 *
887 * In each iteration, check if the next value can be represented in the
888 * current mode we're considering. If it's too large, then step up the
889 * mode to a wider one, and repeat. If it fits, move on to the next
890 * integer. Repeat until the codeword is full, given the current mode.
891 *
892 * Note that we don't have any way to represent unused slots in the
893 * codeword, so we require each codeword to be "full". It is always
894 * possible to produce a full codeword unless the very first delta is too
895 * large to be encoded. For example, if the first delta is small but the
896 * second is too large to be encoded, we'll end up using the last "mode",
897 * which has nints == 1.
898 */
899 selector = 0;
900 nints = simple8b_modes[0].num_ints;
902 diff = ints[0] - base - 1;
903 last_val = ints[0];
904 i = 0; /* number of deltas we have accepted */
905 for (;;)
906 {
907 if (diff >= (UINT64CONST(1) << bits))
908 {
909 /* too large, step up to next mode */
910 selector++;
911 nints = simple8b_modes[selector].num_ints;
912 bits = simple8b_modes[selector].bits_per_int;
913 /* we might already have accepted enough deltas for this mode */
914 if (i >= nints)
915 break;
916 }
917 else
918 {
919 /* accept this delta; then done if codeword is full */
920 i++;
921 if (i >= nints)
922 break;
923 /* examine next delta */
924 Assert(ints[i] > last_val);
925 diff = ints[i] - last_val - 1;
926 last_val = ints[i];
927 }
928 }
929
930 if (nints == 0)
931 {
932 /*
933 * The first delta is too large to be encoded with Simple-8b.
934 *
935 * If there is at least one not-too-large integer in the input, we
936 * will encode it using mode 15 (or a more compact mode). Hence, we
937 * can only get here if the *first* delta is >= 2^60.
938 */
939 Assert(i == 0);
940 *num_encoded = 0;
941 return EMPTY_CODEWORD;
942 }
943
944 /*
945 * Encode the integers using the selected mode. Note that we shift them
946 * into the codeword in reverse order, so that they will come out in the
947 * correct order in the decoder.
948 */
949 codeword = 0;
950 if (bits > 0)
951 {
952 for (i = nints - 1; i > 0; i--)
953 {
954 diff = ints[i] - ints[i - 1] - 1;
955 codeword |= diff;
956 codeword <<= bits;
957 }
958 diff = ints[0] - base - 1;
959 codeword |= diff;
960 }
961
962 /* add selector to the codeword, and return */
963 codeword |= (uint64) selector << 60;
964
965 *num_encoded = nints;
966 return codeword;
967}

References Assert, simple8b_mode::bits_per_int, EMPTY_CODEWORD, i, simple8b_mode::num_ints, simple8b_modes, and UINT64CONST.

Referenced by intset_flush_buffered_values().

Variable Documentation

◆ simple8b_modes

const struct simple8b_mode simple8b_modes[17]
static
Initial value:
=
{
{0, 240},
{0, 120},
{1, 60},
{2, 30},
{3, 20},
{4, 15},
{5, 12},
{6, 10},
{7, 8},
{8, 7},
{10, 6},
{12, 5},
{15, 4},
{20, 3},
{30, 2},
{60, 1},
{0, 0}
}

Referenced by simple8b_contains(), simple8b_decode(), and simple8b_encode().