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author | Junio C Hamano <gitster@pobox.com> | 2009-04-12 23:46:40 (GMT) |
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committer | Junio C Hamano <gitster@pobox.com> | 2009-04-12 23:46:40 (GMT) |
commit | 6e353a5e5de9da021c7c6c0bc2dc5f95a39900a1 (patch) | |
tree | ad981695b0376a42123220d98f3cc4cc74c2ca4b /sha1-lookup.c | |
parent | a54c4edc511608fdba513cc94812c31fd4b497f6 (diff) | |
parent | 13858e5770dd218e5318819d3273c916b46cf8e5 (diff) | |
download | git-6e353a5e5de9da021c7c6c0bc2dc5f95a39900a1.zip git-6e353a5e5de9da021c7c6c0bc2dc5f95a39900a1.tar.gz git-6e353a5e5de9da021c7c6c0bc2dc5f95a39900a1.tar.bz2 |
Merge branch 'cc/bisect-filter'
* cc/bisect-filter: (21 commits)
rev-list: add "int bisect_show_flags" in "struct rev_list_info"
rev-list: remove last static vars used in "show_commit"
list-objects: add "void *data" parameter to show functions
bisect--helper: string output variables together with "&&"
rev-list: pass "int flags" as last argument of "show_bisect_vars"
t6030: test bisecting with paths
bisect: use "bisect--helper" and remove "filter_skipped" function
bisect: implement "read_bisect_paths" to read paths in "$GIT_DIR/BISECT_NAMES"
bisect--helper: implement "git bisect--helper"
bisect: use the new generic "sha1_pos" function to lookup sha1
rev-list: call new "filter_skip" function
patch-ids: use the new generic "sha1_pos" function to lookup sha1
sha1-lookup: add new "sha1_pos" function to efficiently lookup sha1
rev-list: pass "revs" to "show_bisect_vars"
rev-list: make "show_bisect_vars" non static
rev-list: move code to show bisect vars into its own function
rev-list: move bisect related code into its own file
rev-list: make "bisect_list" variable local to "cmd_rev_list"
refs: add "for_each_ref_in" function to refactor "for_each_*_ref" functions
quote: add "sq_dequote_to_argv" to put unwrapped args in an argv array
...
Diffstat (limited to 'sha1-lookup.c')
-rw-r--r-- | sha1-lookup.c | 101 |
1 files changed, 101 insertions, 0 deletions
diff --git a/sha1-lookup.c b/sha1-lookup.c index da35747..055dd87 100644 --- a/sha1-lookup.c +++ b/sha1-lookup.c @@ -1,6 +1,107 @@ #include "cache.h" #include "sha1-lookup.h" +static uint32_t take2(const unsigned char *sha1) +{ + return ((sha1[0] << 8) | sha1[1]); +} + +/* + * Conventional binary search loop looks like this: + * + * do { + * int mi = (lo + hi) / 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 sha1 of element i (between 0 and nr - 1) should be returned + * by "fn(i, table)". + */ +int sha1_pos(const unsigned char *sha1, void *table, size_t nr, + sha1_access_fn fn) +{ + size_t hi = nr; + size_t lo = 0; + size_t mi = 0; + + if (!nr) + return -1; + + if (nr != 1) { + size_t lov, hiv, miv, ofs; + + for (ofs = 0; ofs < 18; ofs += 2) { + lov = take2(fn(0, table) + ofs); + hiv = take2(fn(nr - 1, table) + ofs); + miv = take2(sha1 + ofs); + if (miv < lov) + return -1; + if (hiv < miv) + return -1 - nr; + if (lov != hiv) { + /* + * At this point miv could be equal + * to hiv (but sha1 could still be higher); + * the invariant of (mi < hi) should be + * kept. + */ + mi = (nr - 1) * (miv - lov) / (hiv - lov); + if (lo <= mi && mi < hi) + break; + die("oops"); + } + } + if (18 <= ofs) + die("cannot happen -- lo and hi are identical"); + } + + do { + int cmp; + cmp = hashcmp(fn(mi, table), sha1); + if (!cmp) + return mi; + if (cmp > 0) + hi = mi; + else + lo = mi + 1; + mi = (hi + lo) / 2; + } while (lo < hi); + return -lo-1; +} + /* * Conventional binary search loop looks like this: * |