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   1 #ifndef ITERATOR_H
   2 #define ITERATOR_H
   3
   4 /*
   5  * Generic constants related to iterators.
   6  */
   7
   8 /*
   9  * The attempt to advance the iterator was successful; the iterator
  10  * reflects the new current entry.
  11  */
  12 #define ITER_OK 0
  13
  14 /*
  15  * The iterator is exhausted and has been freed.
  16  */
  17 #define ITER_DONE -1
  18
  19 /*
  20  * The iterator experienced an error. The iteration has been aborted
  21  * and the iterator has been freed.
  22  */
  23 #define ITER_ERROR -2
  24
  25 /*
  26  * Return values for selector functions for merge iterators. The
  27  * numerical values of these constants are important and must be
  28  * compatible with ITER_DONE and ITER_ERROR.
  29  */
  30 enum iterator_selection {
  31         /* End the iteration without an error: */
  32         ITER_SELECT_DONE = ITER_DONE,
  33
  34         /* Report an error and abort the iteration: */
  35         ITER_SELECT_ERROR = ITER_ERROR,
  36
  37         /*
  38          * The next group of constants are masks that are useful
  39          * mainly internally.
  40          */
  41
  42         /* The LSB selects whether iter0/iter1 is the "current" iterator: */
  43         ITER_CURRENT_SELECTION_MASK = 0x01,
  44
  45         /* iter0 is the "current" iterator this round: */
  46         ITER_CURRENT_SELECTION_0 = 0x00,
  47
  48         /* iter1 is the "current" iterator this round: */
  49         ITER_CURRENT_SELECTION_1 = 0x01,
  50
  51         /* Yield the value from the current iterator? */
  52         ITER_YIELD_CURRENT = 0x02,
  53
  54         /* Discard the value from the secondary iterator? */
  55         ITER_SKIP_SECONDARY = 0x04,
  56
  57         /*
  58          * The constants that a selector function should usually
  59          * return.
  60          */
  61
  62         /* Yield the value from iter0: */
  63         ITER_SELECT_0 = ITER_CURRENT_SELECTION_0 | ITER_YIELD_CURRENT,
  64
  65         /* Yield the value from iter0 and discard the one from iter1: */
  66         ITER_SELECT_0_SKIP_1 = ITER_SELECT_0 | ITER_SKIP_SECONDARY,
  67
  68         /* Discard the value from iter0 without yielding anything this round: */
  69         ITER_SKIP_0 = ITER_CURRENT_SELECTION_1 | ITER_SKIP_SECONDARY,
  70
  71         /* Yield the value from iter1: */
  72         ITER_SELECT_1 = ITER_CURRENT_SELECTION_1 | ITER_YIELD_CURRENT,
  73
  74         /* Yield the value from iter1 and discard the one from iter0: */
  75         ITER_SELECT_1_SKIP_0 = ITER_SELECT_1 | ITER_SKIP_SECONDARY,
  76
  77         /* Discard the value from iter1 without yielding anything this round: */
  78         ITER_SKIP_1 = ITER_CURRENT_SELECTION_0 | ITER_SKIP_SECONDARY
  79 };
  80
  81 #endif /* ITERATOR_H */