thodg/libgit2/src/util.h

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• Hash : a7c60cfc
  Author :
  Date : 2009-01-03T02:41:26
  

  Add basic support to read pack-*.idx v1 and v2 files The index data is mapped into memory and then scanned using a binary search algorithm to locate the matching entry for the supplied git_oid. The standard fanout hash trick is applied to reduce the search space by 8 iterations. Since the v1 and v2 file formats differ in their search function, due to the different layouts used for the object records, we use two different search implementations and a virtual function pointer to jump to the correct version of code for the current pack index. The single function jump per-pack should be faster then computing a branch point inside the inner loop of a common binary search. To improve concurrency during read operations the pack lock is only held while verifying the index is actually open, or while opening the index for the first time. This permits multiple concurrent readers to scan through the same index. If an invalid index file is opened we close it and mark the git_pack's invalid bit to true. The git_pack structure is kept around in its parent git_packlist, but the invalid bit will cause all future readers to skip over the pack entirely. Pruning the invalid entries is relatively unimportant because they shouldn't be very common, a $GIT_DIRECTORY/objects/pack directory tends to only have valid pack files. Signed-off-by: Shawn O. Pearce <spearce@spearce.org>

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• src/util.h

• #ifndef INCLUDE_util_h__
  #define INCLUDE_util_h__
  
  #define ARRAY_SIZE(x) (sizeof(x)/sizeof(x[0]))
  
  extern void *git__malloc(size_t);
  extern void *git__calloc(size_t, size_t);
  extern char *git__strdup(const char *);
  
  #ifndef GIT__NO_HIDE_MALLOC
  # define GIT__FORBID_MALLOC do_not_use_malloc_directly
  
  # ifdef malloc
  #  undef malloc
  # endif
  # define malloc(a)          GIT__FORBID_MALLOC
  
  # ifdef calloc
  #  undef calloc
  # endif
  # define calloc(a,b)        GIT__FORBID_MALLOC
  
  # ifdef strdup
  #  undef strdup
  # endif
  # define strdup(a)          GIT__FORBID_MALLOC
  #endif
  
  extern int git__fmt(char *, size_t, const char *, ...)
  	GIT_FORMAT_PRINTF(3, 4);
  extern int git__prefixcmp(const char *str, const char *prefix);
  extern int git__suffixcmp(const char *str, const char *suffix);
  
  /** @return true if p fits into the range of a size_t */
  GIT_INLINE(int) git__is_sizet(off_t p)
  {
  	size_t r = (size_t)p;
  	return p == r;
  }
  
  /*
   * Realloc the buffer pointed at by variable 'x' so that it can hold
   * at least 'nr' entries; the number of entries currently allocated
   * is 'alloc', using the standard growing factor alloc_nr() macro.
   *
   * DO NOT USE any expression with side-effect for 'x' or 'alloc'.
   */
  #define alloc_nr(x) (((x)+16)*3/2)
  #define ALLOC_GROW(x, nr, alloc) \
  	do { \
  		if ((nr) > alloc) { \
  			if (alloc_nr(alloc) < (nr)) \
  				alloc = (nr); \
  			else \
  				alloc = alloc_nr(alloc); \
  			x = xrealloc((x), alloc * sizeof(*(x))); \
  		} \
  	} while(0)
  
  #endif /* INCLUDE_util_h__ */
  

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