From 9ab8fb472f48f42f7e0eebc6f0f986c6c74970e9 Mon Sep 17 00:00:00 2001
From: Taylor Blau <me@ttaylorr.com>
Date: Thu, 15 Aug 2024 18:29:22 -0400
Subject: [PATCH] pack-bitmap.c: keep track of each layer's type bitmaps

Prepare for reading the type-level bitmaps from previous bitmap layers
by maintaining an array for each type, where each element in that type's
array corresponds to one layer's bitmap for that type.

These fields will be used in a later commit to instantiate the 'struct
ewah_or_iterator' for each type.

Signed-off-by: Taylor Blau <me@ttaylorr.com>
---
 pack-bitmap.c | 55 +++++++++++++++++++++++++++++++++++++++++++++++----
 1 file changed, 51 insertions(+), 4 deletions(-)

diff --git a/pack-bitmap.c b/pack-bitmap.c
index 570f6dbdad6546..348488e2d9e241 100644
--- a/pack-bitmap.c
+++ b/pack-bitmap.c
@@ -78,6 +78,24 @@ struct bitmap_index {
 	struct ewah_bitmap *blobs;
 	struct ewah_bitmap *tags;
 
+	/*
+	 * Type index arrays when this bitmap is associated with an
+	 * incremental multi-pack index chain.
+	 *
+	 * If n is the number of unique layers in the MIDX chain, then
+	 * commits_all[n-1] is this structs 'commits' field,
+	 * commits_all[n-2] is the commits field of this bitmap's
+	 * 'base', and so on.
+	 *
+	 * When either associated either with a non-incremental MIDX, or
+	 * a single packfile, these arrays each contain a single
+	 * element.
+	 */
+	struct ewah_bitmap **commits_all;
+	struct ewah_bitmap **trees_all;
+	struct ewah_bitmap **blobs_all;
+	struct ewah_bitmap **tags_all;
+
 	/* Map from object ID -> `stored_bitmap` for all the bitmapped commits */
 	kh_oid_map_t *bitmaps;
 
@@ -586,7 +604,29 @@ static int load_reverse_index(struct repository *r, struct bitmap_index *bitmap_
 	return load_pack_revindex(r, bitmap_git->pack);
 }
 
-static int load_bitmap(struct repository *r, struct bitmap_index *bitmap_git)
+static void load_all_type_bitmaps(struct bitmap_index *bitmap_git)
+{
+	struct bitmap_index *curr = bitmap_git;
+	size_t i = bitmap_git->base_nr - 1;
+
+	ALLOC_ARRAY(bitmap_git->commits_all, bitmap_git->base_nr);
+	ALLOC_ARRAY(bitmap_git->trees_all, bitmap_git->base_nr);
+	ALLOC_ARRAY(bitmap_git->blobs_all, bitmap_git->base_nr);
+	ALLOC_ARRAY(bitmap_git->tags_all, bitmap_git->base_nr);
+
+	while (curr) {
+		bitmap_git->commits_all[i] = curr->commits;
+		bitmap_git->trees_all[i] = curr->trees;
+		bitmap_git->blobs_all[i] = curr->blobs;
+		bitmap_git->tags_all[i] = curr->tags;
+
+		curr = curr->base;
+		i -= 1;
+	}
+}
+
+static int load_bitmap(struct repository *r, struct bitmap_index *bitmap_git,
+		       int recursing)
 {
 	assert(bitmap_git->map);
 
@@ -608,10 +648,13 @@ static int load_bitmap(struct repository *r, struct bitmap_index *bitmap_git)
 	if (bitmap_git->base) {
 		if (!bitmap_is_midx(bitmap_git))
 			BUG("non-MIDX bitmap has non-NULL base bitmap index");
-		if (load_bitmap(r, bitmap_git->base) < 0)
+		if (load_bitmap(r, bitmap_git->base, 1) < 0)
 			goto failed;
 	}
 
+	if (!recursing)
+		load_all_type_bitmaps(bitmap_git);
+
 	return 0;
 
 failed:
@@ -687,7 +730,7 @@ struct bitmap_index *prepare_bitmap_git(struct repository *r)
 {
 	struct bitmap_index *bitmap_git = xcalloc(1, sizeof(*bitmap_git));
 
-	if (!open_bitmap(r, bitmap_git) && !load_bitmap(r, bitmap_git))
+	if (!open_bitmap(r, bitmap_git) && !load_bitmap(r, bitmap_git, 0))
 		return bitmap_git;
 
 	free_bitmap_index(bitmap_git);
@@ -2042,7 +2085,7 @@ struct bitmap_index *prepare_bitmap_walk(struct rev_info *revs,
 	 * from disk. this is the point of no return; after this the rev_list
 	 * becomes invalidated and we must perform the revwalk through bitmaps
 	 */
-	if (load_bitmap(revs->repo, bitmap_git) < 0)
+	if (load_bitmap(revs->repo, bitmap_git, 0) < 0)
 		goto cleanup;
 
 	if (!use_boundary_traversal)
@@ -2961,6 +3004,10 @@ void free_bitmap_index(struct bitmap_index *b)
 	ewah_pool_free(b->trees);
 	ewah_pool_free(b->blobs);
 	ewah_pool_free(b->tags);
+	free(b->commits_all);
+	free(b->trees_all);
+	free(b->blobs_all);
+	free(b->tags_all);
 	if (b->bitmaps) {
 		struct stored_bitmap *sb;
 		kh_foreach_value(b->bitmaps, sb, {