Merge branch 'tb/midx-write'

Code clean-up by splitting code responsible for writing midx files
into its own file.

* tb/midx-write:
  midx-write.c: use `--stdin-packs` when repacking
  midx-write.c: check count of packs to repack after grouping
  midx-write.c: factor out common want_included_pack() routine
  midx-write: move writing-related functions from midx.c

Makefile

@@ -1075,6 +1075,7 @@ LIB_OBJS += merge-ort-wrappers.o
 LIB_OBJS += merge-recursive.o
 LIB_OBJS += merge.o
 LIB_OBJS += midx.o
+LIB_OBJS += midx-write.o
 LIB_OBJS += name-hash.o
 LIB_OBJS += negotiator/default.o
 LIB_OBJS += negotiator/noop.o

midx.h

@@ -8,6 +8,25 @@ struct pack_entry;
 struct repository;
 struct bitmapped_pack;
 
+#define MIDX_SIGNATURE 0x4d494458 /* "MIDX" */
+#define MIDX_VERSION 1
+#define MIDX_BYTE_FILE_VERSION 4
+#define MIDX_BYTE_HASH_VERSION 5
+#define MIDX_BYTE_NUM_CHUNKS 6
+#define MIDX_BYTE_NUM_PACKS 8
+#define MIDX_HEADER_SIZE 12
+
+#define MIDX_CHUNK_ALIGNMENT 4
+#define MIDX_CHUNKID_PACKNAMES 0x504e414d /* "PNAM" */
+#define MIDX_CHUNKID_BITMAPPEDPACKS 0x42544d50 /* "BTMP" */
+#define MIDX_CHUNKID_OIDFANOUT 0x4f494446 /* "OIDF" */
+#define MIDX_CHUNKID_OIDLOOKUP 0x4f49444c /* "OIDL" */
+#define MIDX_CHUNKID_OBJECTOFFSETS 0x4f4f4646 /* "OOFF" */
+#define MIDX_CHUNKID_LARGEOFFSETS 0x4c4f4646 /* "LOFF" */
+#define MIDX_CHUNKID_REVINDEX 0x52494458 /* "RIDX" */
+#define MIDX_CHUNK_OFFSET_WIDTH (2 * sizeof(uint32_t))
+#define MIDX_LARGE_OFFSET_NEEDED 0x80000000
+
 #define GIT_TEST_MULTI_PACK_INDEX "GIT_TEST_MULTI_PACK_INDEX"
 #define GIT_TEST_MULTI_PACK_INDEX_WRITE_BITMAP \
 	"GIT_TEST_MULTI_PACK_INDEX_WRITE_BITMAP"