[PATCH 4/6] builtin/pack-objects.c: learn pack.writeBitmapLookupTable

["Taylor Blau via GitGitGadget" <gitgitgadget@gmail.com>]

From: Taylor Blau <ttaylorr@github.com>

Teach git to provide a way for users to enable/disable bitmap lookup
table extension by providing a config option named 'writeBitmapLookupTable'.

Signed-off-by: Taylor Blau <ttaylorr@github.com>
Signed-off-by: Abhradeep Chakraborty <chakrabortyabhradeep79@gmail.com>
---
 Documentation/config/pack.txt | 7 +++++++
 builtin/pack-objects.c        | 8 ++++++++
 2 files changed, 15 insertions(+)

diff --git a/Documentation/config/pack.txt b/Documentation/config/pack.txt
index ad7f73a1ead..e12008d2415 100644
--- a/Documentation/config/pack.txt
+++ b/Documentation/config/pack.txt
@@ -164,6 +164,13 @@ When writing a multi-pack reachability bitmap, no new namehashes are
 computed; instead, any namehashes stored in an existing bitmap are
 permuted into their appropriate location when writing a new bitmap.
 
+pack.writeBitmapLookupTable::
+	When true, git will include a "lookup table" section in the
+	bitmap index (if one is written). This table is used to defer
+	loading individual bitmaps as late as possible. This can be
+	beneficial in repositories which have relatively large bitmap
+	indexes. Defaults to false.
+
 pack.writeReverseIndex::
 	When true, git will write a corresponding .rev file (see:
 	link:../technical/pack-format.html[Documentation/technical/pack-format.txt])
diff --git a/builtin/pack-objects.c b/builtin/pack-objects.c
index cc5f41086da..3ba20301980 100644
--- a/builtin/pack-objects.c
+++ b/builtin/pack-objects.c
@@ -3148,6 +3148,14 @@ static int git_pack_config(const char *k, const char *v, void *cb)
 		else
 			write_bitmap_options &= ~BITMAP_OPT_HASH_CACHE;
 	}
+
+	if (!strcmp(k, "pack.writebitmaplookuptable")) {
+		if (git_config_bool(k, v))
+			write_bitmap_options |= BITMAP_OPT_LOOKUP_TABLE;
+		else
+			write_bitmap_options &= ~BITMAP_OPT_LOOKUP_TABLE;
+	}
+
 	if (!strcmp(k, "pack.usebitmaps")) {
 		use_bitmap_index_default = git_config_bool(k, v);
 		return 0;
-- 
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