we build a repo which have 3 objects : 1 commit 1 blob 1 tree.

Then, we pack them into packfile and create corresponding IDX and bitmap.

We run a git-pack-objects command to observe the behaviour of indexing with bitmap.

[all matched, all reused]

• 3 objects
• 1 pack (1 idx)
• 1 bitmap
• 0 loose objects

// wants 为 t(111), haves 为 0, 他们存储 压缩前的数据格式

(gdb) print/t bitmap_git.result.word_alloc 
$25 = 1

(gdb) print/t bitmap_git.result.words[0]
$24 = 111

// 打印他们的rlw 值

(gdb) x /g  bitmap_git.commits.rlw
0x100904ae0:    0000000000000000000000000000001000000000000000000000000000000000
(gdb) x /g  bitmap_git.trees.rlw 
0x100904be0:    0000000000000000000000000000001000000000000000000000000000000000
(gdb) x /g  bitmap_git.blobs.rlw 
0x100904ce0:    0000000000000000000000000000001000000000000000000000000000000000
(gdb) x /g  bitmap_git.tags.rlw 
0x100904de0:    0000000000000000000000000000000000000000000000000000000000000000

全部的对象都在reuse bimap中， result中已经不存在任何want objects

(gdb) print bitmap_git->result.words[0]
$8 = 0
(gdb) print bitmap_git->result.word_alloc 
$9 = 1

#0  show_objects_for_type (bitmap_git=0x100904370, object_type=OBJ_COMMIT, 
    show_reach=0x1000bdcc0 <add_object_entry_from_bitmap>) at pack-bitmap.c:1395
#1  0x000000010027403d in traverse_bitmap_commit_list (bitmap_git=0x100904370, revs=0x7ffeefbfda20, 
    show_reachable=0x1000bdcc0 <add_object_entry_from_bitmap>) at pack-bitmap.c:2011

所以这里 traverse_bitmap_commit_list 遍历不到任何值， 遍历result， 遍历个寂寞

nr_remaining = nr_result = 3: 待打包的对象数 : 代表要打包的对象的数量， result的命名不准确，因为result中可能已经 没有值了（比如当前的测试数据下， 所有的对象都在reuse中），所以确切的说应该叫nr_to_pack.

nr_result 有两个地方累加， 一个是 create_object_entry API中， 另一个是reuse计算后的对象，

to_pack: Objects we are going to pack are collected in the to_pack structure. 在 create_object_entry API中， 会将对象添加到 to_pack中。 在本case下， 因为所有的要打包的 对象都在reuse中，所以不会走到create_object_entry API中。故to_pack中没有任何对象。

write_order 为空, 因为to_pack中没有值， to_pack的值 是通过traverse过程中的show_* API写入

➜  pack git:(master) git verify-pack --verbose pack-bbd2e3d4ca6e892f66c32418a00dd15a96f4c037.idx 
5bdcd2a157df7615f2cf9dbb4bee06a6ca9398ac commit 249 135 12
b4de3947675361a7770d29b8982c407b0ec6b2a0 blob   3 12 147
03ded7f5353cffe560d27afb1107e71e1faa8f73 tree   33 44 159
non delta: 3 objects
pack-bbd2e3d4ca6e892f66c32418a00dd15a96f4c037.pack: ok

// 调试命令

sudo gdb --args git  pack-objects --revs --use-bitmap-index --stdout

// wants 为 t(111), haves 为 0, 他们存储 压缩前的数据格式

(gdb) print/t bitmap_git.result.word_alloc $25 = 1

(gdb) print/t bitmap_git.result.words[0] $24 = 111

// 打印他们的rlw 值 (gdb) x /g bitmap_git.commits.rlw 0x100904ae0: 0000000000000000000000000000001000000000000000000000000000000000 (gdb) x /g bitmap_git.trees.rlw 0x100904be0: 0000000000000000000000000000001000000000000000000000000000000000 (gdb) x /g bitmap_git.blobs.rlw 0x100904ce0: 0000000000000000000000000000001000000000000000000000000000000000 (gdb) x /g bitmap_git.tags.rlw 0x100904de0: 0000000000000000000000000000000000000000000000000000000000000000

全部的对象都在reuse bimap中， result中已经不存在任何want objects

(gdb) print bitmap_git->result.words[0] $8 = 0 (gdb) print bitmap_git->result.word_alloc $9 = 1

#0 show_objects_for_type (bitmap_git=0x100904370, object_type=OBJ_COMMIT, show_reach=0x1000bdcc0 <add_object_entry_from_bitmap>) at pack-bitmap.c:1395 #1 0x000000010027403d in traverse_bitmap_commit_list (bitmap_git=0x100904370, revs=0x7ffeefbfda20, show_reachable=0x1000bdcc0 <add_object_entry_from_bitmap>) at pack-bitmap.c:2011

所以这里 traverse_bitmap_commit_list 遍历不到任何值， 遍历result， 遍历个寂寞

nr_remaining = nr_result = 3: 待打包的对象数 : 代表要打包的对象的数量， result的命名不准确，因为result中可能已经 没有值了（比如当前的测试数据下， 所有的对象都在reuse中），所以确切的说应该叫nr_to_pack.

nr_result 有两个地方累加， 一个是 create_object_entry API中， 另一个是reuse计算后的对象，

to_pack: Objects we are going to pack are collected in the to_pack structure. 在 create_object_entry API中， 会将对象添加到 to_pack中。 在本case下， 因为所有的要打包的 对象都在reuse中，所以不会走到create_object_entry API中。故to_pack中没有任何对象。

write_order 为空, 因为to_pack中没有值， to_pack的值 是通过traverse过程中的show_* API写入的