pack-revindex.h

   1 #ifndef PACK_REVINDEX_H
   2 #define PACK_REVINDEX_H
   3
   4 /**
   5  * A revindex allows converting efficiently between three properties
   6  * of an object within a pack:
   7  *
   8  * - index position: the numeric position within the list of sorted object ids
   9  *   found in the .idx file
  10  *
  11  * - pack position: the numeric position within the list of objects in their
  12  *   order within the actual .pack file (i.e., 0 is the first object in the
  13  *   .pack, 1 is the second, and so on)
  14  *
  15  * - offset: the byte offset within the .pack file at which the object contents
  16  *   can be found
  17  */
  18
  19
  20 #define RIDX_SIGNATURE 0x52494458 /* "RIDX" */
  21 #define RIDX_VERSION 1
  22
  23 #define GIT_TEST_WRITE_REV_INDEX "GIT_TEST_WRITE_REV_INDEX"
  24 #define GIT_TEST_REV_INDEX_DIE_IN_MEMORY "GIT_TEST_REV_INDEX_DIE_IN_MEMORY"
  25
  26 struct packed_git;
  27
  28 /*
  29  * load_pack_revindex populates the revindex's internal data-structures for the
  30  * given pack, returning zero on success and a negative value otherwise.
  31  *
  32  * If a '.rev' file is present it is mmap'd, and pointers are assigned into it
  33  * (instead of using the in-memory variant).
  34  */
  35 int load_pack_revindex(struct packed_git *p);
  36
  37 /*
  38  * offset_to_pack_pos converts an object offset to a pack position. This
  39  * function returns zero on success, and a negative number otherwise. The
  40  * parameter 'pos' is usable only on success.
  41  *
  42  * If the reverse index has not yet been loaded, this function loads it lazily,
  43  * and returns an negative number if an error was encountered.
  44  *
  45  * This function runs in time O(log N) with the number of objects in the pack.
  46  */
  47 int offset_to_pack_pos(struct packed_git *p, off_t ofs, uint32_t *pos);
  48
  49 /*
  50  * pack_pos_to_index converts the given pack-relative position 'pos' by
  51  * returning an index-relative position.
  52  *
  53  * If the reverse index has not yet been loaded, or the position is out of
  54  * bounds, this function aborts.
  55  *
  56  * This function runs in constant time.
  57  */
  58 uint32_t pack_pos_to_index(struct packed_git *p, uint32_t pos);
  59
  60 /*
  61  * pack_pos_to_offset converts the given pack-relative position 'pos' into a
  62  * pack offset. For a pack with 'N' objects, asking for position 'N' will return
  63  * the total size (in bytes) of the pack.
  64  *
  65  * If the reverse index has not yet been loaded, or the position is out of
  66  * bounds, this function aborts.
  67  *
  68  * This function runs in constant time under both in-memory and on-disk reverse
  69  * indexes, but an additional step is taken to consult the corresponding .idx
  70  * file when using the on-disk format.
  71  */
  72 off_t pack_pos_to_offset(struct packed_git *p, uint32_t pos);
  73
  74 #endif