Refactor patch-id filtering out of git-cherry and git-format-patch.

This implements the patch-id computation and recording library,
patch-ids.c, and rewrites the get_patch_ids() function used in
cherry and format-patch to use it, so that they do not pollute
the object namespace.  Earlier code threw non-objects into the
in-core object database, and hoped for not getting bitten by
SHA-1 collisions.  While it may be practically Ok, it still was
an ugly hack.

Signed-off-by: Junio C Hamano <junkio@cox.net>

1 files changed, 192 insertions, 0 deletions

diff --git a/patch-ids.c b/patch-ids.c
new file mode 100644
index 0000000000..a288fac992
--- /dev/null
+++ b/patch-ids.c
@@ -0,0 +1,192 @@
+#include "cache.h"
+#include "diff.h"
+#include "commit.h"
+#include "patch-ids.h"
+
+static int commit_patch_id(struct commit *commit, struct diff_options *options,
+		    unsigned char *sha1)
+{
+	if (commit->parents)
+		diff_tree_sha1(commit->parents->item->object.sha1,
+		               commit->object.sha1, "", options);
+	else
+		diff_root_tree_sha1(commit->object.sha1, "", options);
+	diffcore_std(options);
+	return diff_flush_patch_id(options, sha1);
+}
+
+static uint32_t take2(const unsigned char *id)
+{
+	return ((id[0] << 8) | id[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.
+ */
+static int patch_pos(struct patch_id **table, int nr, const unsigned char *id)
+{
+	int hi = nr;
+	int lo = 0;
+	int mi = 0;
+
+	if (!nr)
+		return -1;
+
+	if (nr != 1) {
+		unsigned lov, hiv, miv, ofs;
+
+		for (ofs = 0; ofs < 18; ofs += 2) {
+			lov = take2(table[0]->patch_id + ofs);
+			hiv = take2(table[nr-1]->patch_id + ofs);
+			miv = take2(id + 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 id 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(table[mi]->patch_id, id);
+		if (!cmp)
+			return mi;
+		if (cmp > 0)
+			hi = mi;
+		else
+			lo = mi + 1;
+		mi = (hi + lo) / 2;
+	} while (lo < hi);
+	return -lo-1;
+}
+
+#define BUCKET_SIZE 190 /* 190 * 21 = 3990, with slop close enough to 4K */
+struct patch_id_bucket {
+	struct patch_id_bucket *next;
+	int nr;
+	struct patch_id bucket[BUCKET_SIZE];
+};
+
+int init_patch_ids(struct patch_ids *ids)
+{
+	memset(ids, 0, sizeof(*ids));
+	diff_setup(&ids->diffopts);
+	ids->diffopts.recursive = 1;
+	if (diff_setup_done(&ids->diffopts) < 0)
+		return error("diff_setup_done failed");
+	return 0;
+}
+
+int free_patch_ids(struct patch_ids *ids)
+{
+	struct patch_id_bucket *next, *patches;
+
+	free(ids->table);
+	for (patches = ids->patches; patches; patches = next) {
+		next = patches->next;
+		free(patches);
+	}
+	return 0;
+}
+
+static struct patch_id *add_commit(struct commit *commit,
+				   struct patch_ids *ids,
+				   int no_add)
+{
+	struct patch_id_bucket *bucket;
+	struct patch_id *ent;
+	unsigned char sha1[20];
+	int pos;
+
+	if (commit_patch_id(commit, &ids->diffopts, sha1))
+		return NULL;
+	pos = patch_pos(ids->table, ids->nr, sha1);
+	if (0 <= pos)
+		return ids->table[pos];
+	if (no_add)
+		return NULL;
+
+	pos = -1 - pos;
+
+	bucket = ids->patches;
+	if (!bucket || (BUCKET_SIZE <= bucket->nr)) {
+		bucket = xcalloc(1, sizeof(*bucket));
+		bucket->next = ids->patches;
+		ids->patches = bucket;
+	}
+	ent = &bucket->bucket[bucket->nr++];
+	hashcpy(ent->patch_id, sha1);
+
+	if (ids->alloc <= ids->nr) {
+		ids->alloc = alloc_nr(ids->nr);
+		ids->table = xrealloc(ids->table, sizeof(ent) * ids->alloc);
+	}
+	if (pos < ids->nr)
+		memmove(ids->table + pos + 1, ids->table + pos,
+			sizeof(ent) * (ids->nr - pos));
+	ids->nr++;
+	ids->table[pos] = ent;
+	return ids->table[pos];
+}
+
+struct patch_id *has_commit_patch_id(struct commit *commit,
+				     struct patch_ids *ids)
+{
+	return add_commit(commit, ids, 1);
+}
+
+struct patch_id *add_commit_patch_id(struct commit *commit,
+				     struct patch_ids *ids)
+{
+	return add_commit(commit, ids, 0);
+}