219 lines
6.7 KiB
C
219 lines
6.7 KiB
C
/* SparseSet implementation.
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Copyright (C) 2007-2023 Free Software Foundation, Inc.
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Contributed by Peter Bergner <bergner@vnet.ibm.com>
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This file is part of GCC.
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GCC is free software; you can redistribute it and/or modify it under
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the terms of the GNU General Public License as published by the Free
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Software Foundation; either version 3, or (at your option) any later
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version.
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GCC is distributed in the hope that it will be useful, but WITHOUT ANY
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WARRANTY; without even the implied warranty of MERCHANTABILITY or
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FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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for more details.
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You should have received a copy of the GNU General Public License
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along with GCC; see the file COPYING3. If not see
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<http://www.gnu.org/licenses/>. */
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#ifndef GCC_SPARSESET_H
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#define GCC_SPARSESET_H
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/* Implementation of the Briggs and Torczon sparse set representation.
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The sparse set representation was first published in:
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"An Efficient Representation for Sparse Sets",
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ACM LOPLAS, Vol. 2, Nos. 1-4, March-December 1993, Pages 59-69.
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The sparse set representation is suitable for integer sets with a
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fixed-size universe. Two vectors are used to store the members of
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the set. If an element I is in the set, then sparse[I] is the
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index of I in the dense vector, and dense[sparse[I]] == I. The dense
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vector works like a stack. The size of the stack is the cardinality
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of the set.
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The following operations can be performed in O(1) time:
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* clear : sparseset_clear
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* cardinality : sparseset_cardinality
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* set_size : sparseset_size
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* member_p : sparseset_bit_p
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* add_member : sparseset_set_bit
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* remove_member : sparseset_clear_bit
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* choose_one : sparseset_pop
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Additionally, the sparse set representation supports enumeration of
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the members in O(N) time, where n is the number of members in the set.
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The members of the set are stored cache-friendly in the dense vector.
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This makes it a competitive choice for iterating over relatively sparse
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sets requiring operations:
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* forall : EXECUTE_IF_SET_IN_SPARSESET
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* set_copy : sparseset_copy
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* set_intersection : sparseset_and
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* set_union : sparseset_ior
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* set_difference : sparseset_and_compl
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* set_disjuction : (not implemented)
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* set_compare : sparseset_equal_p
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NB: It is OK to use remove_member during EXECUTE_IF_SET_IN_SPARSESET.
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The iterator is updated for it.
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Based on the efficiency of these operations, this representation of
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sparse sets will often be superior to alternatives such as simple
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bitmaps, linked-list bitmaps, array bitmaps, balanced binary trees,
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hash tables, linked lists, etc., if the set is sufficiently sparse.
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In the LOPLAS paper the cut-off point where sparse sets became faster
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than simple bitmaps (see sbitmap.h) when N / U < 64 (where U is the
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size of the universe of the set).
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Because the set universe is fixed, the set cannot be resized. For
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sparse sets with initially unknown size, linked-list bitmaps are a
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better choice, see bitmap.h.
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Sparse sets storage requirements are relatively large: O(U) with a
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larger constant than sbitmaps (if the storage requirement for an
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sbitmap with universe U is S, then the storage required for a sparse
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set for the same universe are 2 * sizeof (SPARSESET_ELT_TYPE) * 8 * S).
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Accessing the sparse vector is not very cache-friendly, but iterating
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over the members in the set is cache-friendly because only the dense
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vector is used. */
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/* Data Structure used for the SparseSet representation. */
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#define SPARSESET_ELT_TYPE unsigned int
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typedef struct sparseset_def
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{
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SPARSESET_ELT_TYPE *dense; /* Dense array. */
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SPARSESET_ELT_TYPE *sparse; /* Sparse array. */
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SPARSESET_ELT_TYPE members; /* Number of elements. */
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SPARSESET_ELT_TYPE size; /* Maximum number of elements. */
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SPARSESET_ELT_TYPE iter; /* Iterator index. */
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unsigned char iter_inc; /* Iteration increment amount. */
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bool iterating;
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SPARSESET_ELT_TYPE elms[2]; /* Combined dense and sparse arrays. */
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} *sparseset;
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#define sparseset_free(MAP) free(MAP)
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extern sparseset sparseset_alloc (SPARSESET_ELT_TYPE n_elms);
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extern void sparseset_clear_bit (sparseset, SPARSESET_ELT_TYPE);
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extern void sparseset_copy (sparseset, sparseset);
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extern void sparseset_and (sparseset, sparseset, sparseset);
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extern void sparseset_and_compl (sparseset, sparseset, sparseset);
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extern void sparseset_ior (sparseset, sparseset, sparseset);
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extern bool sparseset_equal_p (sparseset, sparseset);
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/* Operation: S = {}
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Clear the set of all elements. */
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inline void
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sparseset_clear (sparseset s)
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{
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s->members = 0;
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s->iterating = false;
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}
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/* Return the number of elements currently in the set. */
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inline SPARSESET_ELT_TYPE
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sparseset_cardinality (sparseset s)
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{
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return s->members;
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}
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/* Return the maximum number of elements this set can hold. */
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inline SPARSESET_ELT_TYPE
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sparseset_size (sparseset s)
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{
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return s->size;
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}
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/* Return true if e is a member of the set S, otherwise return false. */
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inline bool
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sparseset_bit_p (sparseset s, SPARSESET_ELT_TYPE e)
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{
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SPARSESET_ELT_TYPE idx;
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gcc_checking_assert (e < s->size);
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idx = s->sparse[e];
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return idx < s->members && s->dense[idx] == e;
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}
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/* Low level insertion routine not meant for use outside of sparseset.[ch].
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Assumes E is valid and not already a member of the set S. */
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inline void
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sparseset_insert_bit (sparseset s, SPARSESET_ELT_TYPE e, SPARSESET_ELT_TYPE idx)
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{
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s->sparse[e] = idx;
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s->dense[idx] = e;
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}
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/* Operation: S = S + {e}
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Insert E into the set S, if it isn't already a member. */
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inline void
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sparseset_set_bit (sparseset s, SPARSESET_ELT_TYPE e)
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{
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if (!sparseset_bit_p (s, e))
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sparseset_insert_bit (s, e, s->members++);
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}
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/* Return and remove the last member added to the set S. */
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inline SPARSESET_ELT_TYPE
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sparseset_pop (sparseset s)
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{
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SPARSESET_ELT_TYPE mem = s->members;
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gcc_checking_assert (mem != 0);
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s->members = mem - 1;
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return s->dense[s->members];
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}
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inline void
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sparseset_iter_init (sparseset s)
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{
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s->iter = 0;
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s->iter_inc = 1;
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s->iterating = true;
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}
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inline bool
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sparseset_iter_p (sparseset s)
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{
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if (s->iterating && s->iter < s->members)
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return true;
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else
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return s->iterating = false;
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}
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inline SPARSESET_ELT_TYPE
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sparseset_iter_elm (sparseset s)
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{
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return s->dense[s->iter];
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}
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inline void
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sparseset_iter_next (sparseset s)
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{
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s->iter += s->iter_inc;
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s->iter_inc = 1;
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}
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#define EXECUTE_IF_SET_IN_SPARSESET(SPARSESET, ITER) \
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for (sparseset_iter_init (SPARSESET); \
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sparseset_iter_p (SPARSESET) \
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&& (((ITER) = sparseset_iter_elm (SPARSESET)) || 1); \
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sparseset_iter_next (SPARSESET))
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#endif /* GCC_SPARSESET_H */
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