pack-bitmap-write.c: write pseudo-merge table

Now that the pack-bitmap writer machinery understands how to select and
store pseudo-merge commits, teach it how to write the new optional
pseudo-merge .bitmap extension.

No readers yet exist for this new extension to the .bitmap format. The
following commits will take any preparatory step(s) necessary before
then implementing the routines necessary to read this new table.

In the meantime, the new `write_pseudo_merges()` function implements
writing this new format as described by a previous commit in
Documentation/technical/bitmap-format.txt.

Writing this table is fairly straightforward and consists of a few
sub-components:

  - a pair of bitmaps for each pseudo-merge (one for the pseudo-merge
    "parents", and another for the objects reachable from those parents)

  - for each commit, the offset of either (a) the pseudo-merge it
    belongs to, or (b) an extended lookup table if it belongs to >1
    pseudo-merge groups

  - if there are any commits belonging to >1 pseudo-merge group, the
    extended lookup tables (which each consist of the number of
    pseudo-merge groups a commit appears in, and then that many 4-byte
    unsigned )

Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

pack-bitmap-write.c

@@ -18,6 +18,7 @@
 #include "tree.h"
 #include "tree-walk.h"
 #include "pseudo-merge.h"
+#include "oid-array.h"
 
 struct bitmapped_commit {
 	struct commit *commit;
@@ -771,6 +772,130 @@ static void write_selected_commits_v1(struct bitmap_writer *writer,
 	}
 }
 
+static void write_pseudo_merges(struct bitmap_writer *writer,
+				struct hashfile *f)
+{
+	struct oid_array commits = OID_ARRAY_INIT;
+	struct bitmap **commits_bitmap = NULL;
+	off_t *pseudo_merge_ofs = NULL;
+	off_t start, table_start, next_ext;
+
+	uint32_t base = bitmap_writer_nr_selected_commits(writer);
+	size_t i, j = 0;
+
+	CALLOC_ARRAY(commits_bitmap, writer->pseudo_merges_nr);
+	CALLOC_ARRAY(pseudo_merge_ofs, writer->pseudo_merges_nr);
+
+	for (i = 0; i < writer->pseudo_merges_nr; i++) {
+		struct bitmapped_commit *merge = &writer->selected[base + i];
+		struct commit_list *p;
+
+		if (!merge->pseudo_merge)
+			BUG("found non-pseudo merge commit at %"PRIuMAX, (uintmax_t)i);
+
+		commits_bitmap[i] = bitmap_new();
+
+		for (p = merge->commit->parents; p; p = p->next)
+			bitmap_set(commits_bitmap[i],
+				   find_object_pos(writer, &p->item->object.oid,
+						   NULL));
+	}
+
+	start = hashfile_total(f);
+
+	for (i = 0; i < writer->pseudo_merges_nr; i++) {
+		struct ewah_bitmap *commits_ewah = bitmap_to_ewah(commits_bitmap[i]);
+
+		pseudo_merge_ofs[i] = hashfile_total(f);
+
+		dump_bitmap(f, commits_ewah);
+		dump_bitmap(f, writer->selected[base+i].write_as);
+
+		ewah_free(commits_ewah);
+	}
+
+	next_ext = st_add(hashfile_total(f),
+			  st_mult(kh_size(writer->pseudo_merge_commits),
+				  sizeof(uint64_t)));
+
+	table_start = hashfile_total(f);
+
+	commits.alloc = kh_size(writer->pseudo_merge_commits);
+	CALLOC_ARRAY(commits.oid, commits.alloc);
+
+	for (i = kh_begin(writer->pseudo_merge_commits); i != kh_end(writer->pseudo_merge_commits); i++) {
+		if (!kh_exist(writer->pseudo_merge_commits, i))
+			continue;
+		oid_array_append(&commits, &kh_key(writer->pseudo_merge_commits, i));
+	}
+
+	oid_array_sort(&commits);
+
+	/* write lookup table (non-extended) */
+	for (i = 0; i < commits.nr; i++) {
+		int hash_pos;
+		struct pseudo_merge_commit_idx *c;
+
+		hash_pos = kh_get_oid_map(writer->pseudo_merge_commits,
+					  commits.oid[i]);
+		if (hash_pos == kh_end(writer->pseudo_merge_commits))
+			BUG("could not find pseudo-merge commit %s",
+			    oid_to_hex(&commits.oid[i]));
+
+		c = kh_value(writer->pseudo_merge_commits, hash_pos);
+
+		hashwrite_be32(f, find_object_pos(writer, &commits.oid[i],
+						  NULL));
+		if (c->nr == 1)
+			hashwrite_be64(f, pseudo_merge_ofs[c->pseudo_merge[0]]);
+		else if (c->nr > 1) {
+			if (next_ext & ((uint64_t)1<<63))
+				die(_("too many pseudo-merges"));
+			hashwrite_be64(f, next_ext | ((uint64_t)1<<63));
+			next_ext = st_add3(next_ext,
+					   sizeof(uint32_t),
+					   st_mult(c->nr, sizeof(uint64_t)));
+		} else
+			BUG("expected commit '%s' to have at least one "
+			    "pseudo-merge", oid_to_hex(&commits.oid[i]));
+	}
+
+	/* write lookup table (extended) */
+	for (i = 0; i < commits.nr; i++) {
+		int hash_pos;
+		struct pseudo_merge_commit_idx *c;
+
+		hash_pos = kh_get_oid_map(writer->pseudo_merge_commits,
+					  commits.oid[i]);
+		if (hash_pos == kh_end(writer->pseudo_merge_commits))
+			BUG("could not find pseudo-merge commit %s",
+			    oid_to_hex(&commits.oid[i]));
+
+		c = kh_value(writer->pseudo_merge_commits, hash_pos);
+		if (c->nr == 1)
+			continue;
+
+		hashwrite_be32(f, c->nr);
+		for (j = 0; j < c->nr; j++)
+			hashwrite_be64(f, pseudo_merge_ofs[c->pseudo_merge[j]]);
+	}
+
+	/* write positions for all pseudo merges */
+	for (i = 0; i < writer->pseudo_merges_nr; i++)
+		hashwrite_be64(f, pseudo_merge_ofs[i]);
+
+	hashwrite_be32(f, writer->pseudo_merges_nr);
+	hashwrite_be32(f, kh_size(writer->pseudo_merge_commits));
+	hashwrite_be64(f, table_start - start);
+	hashwrite_be64(f, hashfile_total(f) - start + sizeof(uint64_t));
+
+	for (i = 0; i < writer->pseudo_merges_nr; i++)
+		bitmap_free(commits_bitmap[i]);
+
+	free(pseudo_merge_ofs);
+	free(commits_bitmap);
+}
+
 static int table_cmp(const void *_va, const void *_vb, void *_data)
 {
 	struct bitmap_writer *writer = _data;
@@ -878,6 +1003,9 @@ void bitmap_writer_finish(struct bitmap_writer *writer,
 
 	int fd = odb_mkstemp(&tmp_file, "pack/tmp_bitmap_XXXXXX");
 
+	if (writer->pseudo_merges_nr)
+		options |= BITMAP_OPT_PSEUDO_MERGES;
+
 	f = hashfd(fd, tmp_file.buf);
 
 	memcpy(header.magic, BITMAP_IDX_SIGNATURE, sizeof(BITMAP_IDX_SIGNATURE));
@@ -907,6 +1035,9 @@ void bitmap_writer_finish(struct bitmap_writer *writer,
 
 	write_selected_commits_v1(writer, f, offsets);
 
+	if (options & BITMAP_OPT_PSEUDO_MERGES)
+		write_pseudo_merges(writer, f);
+
 	if (options & BITMAP_OPT_LOOKUP_TABLE)
 		write_lookup_table(writer, f, offsets);
 

pack-bitmap.h

@@ -37,6 +37,7 @@ enum pack_bitmap_opts {
 	BITMAP_OPT_FULL_DAG = 0x1,
 	BITMAP_OPT_HASH_CACHE = 0x4,
 	BITMAP_OPT_LOOKUP_TABLE = 0x10,
+	BITMAP_OPT_PSEUDO_MERGES = 0x20,
 };
 
 enum pack_bitmap_flags {