git

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#define USE_THE_REPOSITORY_VARIABLE
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#include "git-compat-util.h"
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#include "hash.h"
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#include "hash-lookup.h"
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#include "read-cache-ll.h"
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static uint32_t take2(const struct object_id *oid, size_t ofs)
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{
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	return ((oid->hash[ofs] << 8) | oid->hash[ofs + 1]);
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}
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/*
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 * Conventional binary search loop looks like this:
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 *
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 *      do {
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 *              int mi = lo + (hi - lo) / 2;
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 *              int cmp = "entry pointed at by mi" minus "target";
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 *              if (!cmp)
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 *                      return (mi is the wanted one)
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 *              if (cmp > 0)
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 *                      hi = mi; "mi is larger than target"
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 *              else
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 *                      lo = mi+1; "mi is smaller than target"
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 *      } while (lo < hi);
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 *
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 * The invariants are:
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 *
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 * - When entering the loop, lo points at a slot that is never
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 *   above the target (it could be at the target), hi points at a
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 *   slot that is guaranteed to be above the target (it can never
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 *   be at the target).
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 *
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 * - We find a point 'mi' between lo and hi (mi could be the same
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 *   as lo, but never can be the same as hi), and check if it hits
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 *   the target.  There are three cases:
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 *
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 *    - if it is a hit, we are happy.
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 *
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 *    - if it is strictly higher than the target, we update hi with
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 *      it.
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 *
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 *    - if it is strictly lower than the target, we update lo to be
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 *      one slot after it, because we allow lo to be at the target.
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 *
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 * When choosing 'mi', we do not have to take the "middle" but
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 * anywhere in between lo and hi, as long as lo <= mi < hi is
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 * satisfied.  When we somehow know that the distance between the
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 * target and lo is much shorter than the target and hi, we could
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 * pick mi that is much closer to lo than the midway.
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 */
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/*
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 * The table should contain "nr" elements.
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 * The oid of element i (between 0 and nr - 1) should be returned
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 * by "fn(i, table)".
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 */
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int oid_pos(const struct object_id *oid, const void *table, size_t nr,
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	    oid_access_fn fn)
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{
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	size_t hi = nr;
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	size_t lo = 0;
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	size_t mi = 0;
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	if (!nr)
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		return -1;
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	if (nr != 1) {
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		size_t lov, hiv, miv, ofs;
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		for (ofs = 0; ofs < the_hash_algo->rawsz - 2; ofs += 2) {
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			lov = take2(fn(0, table), ofs);
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			hiv = take2(fn(nr - 1, table), ofs);
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			miv = take2(oid, ofs);
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			if (miv < lov)
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				return -1;
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			if (hiv < miv)
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				return index_pos_to_insert_pos(nr);
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			if (lov != hiv) {
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				/*
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				 * At this point miv could be equal
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				 * to hiv (but hash could still be higher);
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				 * the invariant of (mi < hi) should be
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				 * kept.
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				 */
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				mi = (nr - 1) * (miv - lov) / (hiv - lov);
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				if (lo <= mi && mi < hi)
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					break;
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				BUG("assertion failed in binary search");
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			}
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		}
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	}
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	do {
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		int cmp;
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		cmp = oidcmp(fn(mi, table), oid);
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		if (!cmp)
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			return mi;
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		if (cmp > 0)
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			hi = mi;
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		else
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			lo = mi + 1;
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		mi = lo + (hi - lo) / 2;
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	} while (lo < hi);
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	return index_pos_to_insert_pos(lo);
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}
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int bsearch_hash(const unsigned char *hash, const uint32_t *fanout_nbo,
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		 const unsigned char *table, size_t stride, uint32_t *result)
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{
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	uint32_t hi, lo;
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	hi = ntohl(fanout_nbo[*hash]);
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	lo = ((*hash == 0x0) ? 0 : ntohl(fanout_nbo[*hash - 1]));
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	while (lo < hi) {
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		unsigned mi = lo + (hi - lo) / 2;
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		int cmp = hashcmp(table + mi * stride, hash,
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				  the_repository->hash_algo);
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		if (!cmp) {
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			if (result)
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				*result = mi;
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			return 1;
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		}
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		if (cmp > 0)
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			hi = mi;
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		else
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			lo = mi + 1;
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	}
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	if (result)
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		*result = lo;
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	return 0;
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}
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