git/hash-lookup.c

#define USE_THE_REPOSITORY_VARIABLE

#include "git-compat-util.h"
#include "hash.h"
#include "hash-lookup.h"
#include "read-cache-ll.h"

static uint32_t take2(const struct object_id *oid, size_t ofs)
{ … }

/*
 * Conventional binary search loop looks like this:
 *
 *      do {
 *              int mi = lo + (hi - lo) / 2;
 *              int cmp = "entry pointed at by mi" minus "target";
 *              if (!cmp)
 *                      return (mi is the wanted one)
 *              if (cmp > 0)
 *                      hi = mi; "mi is larger than target"
 *              else
 *                      lo = mi+1; "mi is smaller than target"
 *      } while (lo < hi);
 *
 * The invariants are:
 *
 * - When entering the loop, lo points at a slot that is never
 *   above the target (it could be at the target), hi points at a
 *   slot that is guaranteed to be above the target (it can never
 *   be at the target).
 *
 * - We find a point 'mi' between lo and hi (mi could be the same
 *   as lo, but never can be the same as hi), and check if it hits
 *   the target.  There are three cases:
 *
 *    - if it is a hit, we are happy.
 *
 *    - if it is strictly higher than the target, we update hi with
 *      it.
 *
 *    - if it is strictly lower than the target, we update lo to be
 *      one slot after it, because we allow lo to be at the target.
 *
 * When choosing 'mi', we do not have to take the "middle" but
 * anywhere in between lo and hi, as long as lo <= mi < hi is
 * satisfied.  When we somehow know that the distance between the
 * target and lo is much shorter than the target and hi, we could
 * pick mi that is much closer to lo than the midway.
 */
/*
 * The table should contain "nr" elements.
 * The oid of element i (between 0 and nr - 1) should be returned
 * by "fn(i, table)".
 */
int oid_pos(const struct object_id *oid, const void *table, size_t nr,
	    oid_access_fn fn)
{ … }

int bsearch_hash(const unsigned char *hash, const uint32_t *fanout_nbo,
		 const unsigned char *table, size_t stride, uint32_t *result)
{ … }