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1 /* SparseSet implementation.
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2 Copyright (C) 2007-2018 Free Software Foundation, Inc.
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3 Contributed by Peter Bergner <bergner@vnet.ibm.com>
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4
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5 This file is part of GCC.
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6
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7 GCC is free software; you can redistribute it and/or modify it under
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8 the terms of the GNU General Public License as published by the Free
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9 Software Foundation; either version 3, or (at your option) any later
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10 version.
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11
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12 GCC is distributed in the hope that it will be useful, but WITHOUT ANY
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13 WARRANTY; without even the implied warranty of MERCHANTABILITY or
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14 FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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15 for more details.
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16
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17 You should have received a copy of the GNU General Public License
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18 along with GCC; see the file COPYING3. If not see
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19 <http://www.gnu.org/licenses/>. */
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20
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21 #ifndef GCC_SPARSESET_H
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22 #define GCC_SPARSESET_H
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23
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111
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24 /* Implementation of the Briggs and Torczon sparse set representation.
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25 The sparse set representation was first published in:
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26
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27 "An Efficient Representation for Sparse Sets",
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28 ACM LOPLAS, Vol. 2, Nos. 1-4, March-December 1993, Pages 59-69.
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29
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30 The sparse set representation is suitable for integer sets with a
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31 fixed-size universe. Two vectors are used to store the members of
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32 the set. If an element I is in the set, then sparse[I] is the
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33 index of I in the dense vector, and dense[sparse[I]] == I. The dense
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34 vector works like a stack. The size of the stack is the cardinality
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35 of the set.
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36
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37 The following operations can be performed in O(1) time:
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38
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39 * clear : sparseset_clear
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40 * cardinality : sparseset_cardinality
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41 * set_size : sparseset_size
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42 * member_p : sparseset_bit_p
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43 * add_member : sparseset_set_bit
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44 * remove_member : sparseset_clear_bit
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45 * choose_one : sparseset_pop
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46
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47 Additionally, the sparse set representation supports enumeration of
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48 the members in O(N) time, where n is the number of members in the set.
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49 The members of the set are stored cache-friendly in the dense vector.
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50 This makes it a competitive choice for iterating over relatively sparse
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51 sets requiring operations:
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52
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53 * forall : EXECUTE_IF_SET_IN_SPARSESET
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54 * set_copy : sparseset_copy
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55 * set_intersection : sparseset_and
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56 * set_union : sparseset_ior
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57 * set_difference : sparseset_and_compl
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58 * set_disjuction : (not implemented)
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59 * set_compare : sparseset_equal_p
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60
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61 NB: It is OK to use remove_member during EXECUTE_IF_SET_IN_SPARSESET.
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62 The iterator is updated for it.
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63
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64 Based on the efficiency of these operations, this representation of
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65 sparse sets will often be superior to alternatives such as simple
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66 bitmaps, linked-list bitmaps, array bitmaps, balanced binary trees,
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67 hash tables, linked lists, etc., if the set is sufficiently sparse.
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68 In the LOPLAS paper the cut-off point where sparse sets became faster
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69 than simple bitmaps (see sbitmap.h) when N / U < 64 (where U is the
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70 size of the universe of the set).
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71
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72 Because the set universe is fixed, the set cannot be resized. For
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73 sparse sets with initially unknown size, linked-list bitmaps are a
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74 better choice, see bitmap.h.
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75
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76 Sparse sets storage requirements are relatively large: O(U) with a
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77 larger constant than sbitmaps (if the storage requirement for an
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78 sbitmap with universe U is S, then the storage required for a sparse
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79 set for the same universe are 2*HOST_BITS_PER_WIDEST_FAST_INT * S).
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80 Accessing the sparse vector is not very cache-friendly, but iterating
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81 over the members in the set is cache-friendly because only the dense
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82 vector is used. */
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83
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84 /* Data Structure used for the SparseSet representation. */
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85
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86 #define SPARSESET_ELT_BITS ((unsigned) HOST_BITS_PER_WIDEST_FAST_INT)
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87 #define SPARSESET_ELT_TYPE unsigned HOST_WIDEST_FAST_INT
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88
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89 typedef struct sparseset_def
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90 {
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91 SPARSESET_ELT_TYPE *dense; /* Dense array. */
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92 SPARSESET_ELT_TYPE *sparse; /* Sparse array. */
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93 SPARSESET_ELT_TYPE members; /* Number of elements. */
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94 SPARSESET_ELT_TYPE size; /* Maximum number of elements. */
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95 SPARSESET_ELT_TYPE iter; /* Iterator index. */
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96 unsigned char iter_inc; /* Iteration increment amount. */
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97 bool iterating;
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98 SPARSESET_ELT_TYPE elms[2]; /* Combined dense and sparse arrays. */
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99 } *sparseset;
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100
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101 #define sparseset_free(MAP) free(MAP)
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102 extern sparseset sparseset_alloc (SPARSESET_ELT_TYPE n_elms);
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103 extern void sparseset_clear_bit (sparseset, SPARSESET_ELT_TYPE);
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104 extern void sparseset_copy (sparseset, sparseset);
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105 extern void sparseset_and (sparseset, sparseset, sparseset);
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106 extern void sparseset_and_compl (sparseset, sparseset, sparseset);
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107 extern void sparseset_ior (sparseset, sparseset, sparseset);
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108 extern bool sparseset_equal_p (sparseset, sparseset);
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109
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110 /* Operation: S = {}
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111 Clear the set of all elements. */
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112
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113 static inline void
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114 sparseset_clear (sparseset s)
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115 {
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116 s->members = 0;
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117 s->iterating = false;
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118 }
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119
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120 /* Return the number of elements currently in the set. */
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121
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122 static inline SPARSESET_ELT_TYPE
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123 sparseset_cardinality (sparseset s)
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124 {
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125 return s->members;
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126 }
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127
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128 /* Return the maximum number of elements this set can hold. */
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129
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130 static inline SPARSESET_ELT_TYPE
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131 sparseset_size (sparseset s)
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132 {
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133 return s->size;
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134 }
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135
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136 /* Return true if e is a member of the set S, otherwise return false. */
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137
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138 static inline bool
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139 sparseset_bit_p (sparseset s, SPARSESET_ELT_TYPE e)
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140 {
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141 SPARSESET_ELT_TYPE idx;
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142
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143 gcc_checking_assert (e < s->size);
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144
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145 idx = s->sparse[e];
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146
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147 return idx < s->members && s->dense[idx] == e;
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148 }
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149
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150 /* Low level insertion routine not meant for use outside of sparseset.[ch].
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151 Assumes E is valid and not already a member of the set S. */
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152
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153 static inline void
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154 sparseset_insert_bit (sparseset s, SPARSESET_ELT_TYPE e, SPARSESET_ELT_TYPE idx)
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155 {
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156 s->sparse[e] = idx;
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157 s->dense[idx] = e;
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158 }
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159
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160 /* Operation: S = S + {e}
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161 Insert E into the set S, if it isn't already a member. */
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162
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163 static inline void
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164 sparseset_set_bit (sparseset s, SPARSESET_ELT_TYPE e)
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165 {
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166 if (!sparseset_bit_p (s, e))
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167 sparseset_insert_bit (s, e, s->members++);
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168 }
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169
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170 /* Return and remove the last member added to the set S. */
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171
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172 static inline SPARSESET_ELT_TYPE
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173 sparseset_pop (sparseset s)
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174 {
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175 SPARSESET_ELT_TYPE mem = s->members;
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176
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177 gcc_checking_assert (mem != 0);
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178
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179 s->members = mem - 1;
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180 return s->dense[s->members];
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181 }
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182
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183 static inline void
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184 sparseset_iter_init (sparseset s)
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185 {
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186 s->iter = 0;
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187 s->iter_inc = 1;
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188 s->iterating = true;
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189 }
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190
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191 static inline bool
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192 sparseset_iter_p (sparseset s)
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193 {
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194 if (s->iterating && s->iter < s->members)
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195 return true;
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196 else
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197 return s->iterating = false;
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198 }
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199
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200 static inline SPARSESET_ELT_TYPE
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201 sparseset_iter_elm (sparseset s)
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202 {
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203 return s->dense[s->iter];
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204 }
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205
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206 static inline void
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207 sparseset_iter_next (sparseset s)
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208 {
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209 s->iter += s->iter_inc;
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210 s->iter_inc = 1;
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211 }
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212
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213 #define EXECUTE_IF_SET_IN_SPARSESET(SPARSESET, ITER) \
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214 for (sparseset_iter_init (SPARSESET); \
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215 sparseset_iter_p (SPARSESET) \
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216 && (((ITER) = sparseset_iter_elm (SPARSESET)) || 1); \
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217 sparseset_iter_next (SPARSESET))
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218
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219 #endif /* GCC_SPARSESET_H */
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