pack: unpack using a loop

We currently make use of recursive function calls to unpack an object,
resolving the deltas as we come back down the chain. This means that we
have unbounded stack growth as we look up objects in a pack.

This is now done in two steps: first we figure out what the dependency
chain is by looking up the delta bases until we reach a non-delta
object, pushing the information we need onto a stack and then we pop
from that stack and apply the deltas until there are no more left.

This version of the code does not make use of the delta base cache so it
is slower than what's in the mainline. A later commit will reintroduce
it.

1 files changed, 9 insertions, 0 deletions

diff --git a/src/pack.h b/src/pack.h
index 58f81e2f0..a2ea3849f 100644
--- a/src/pack.h
+++ b/src/pack.h
@@ -17,6 +17,7 @@
 #include "mwindow.h"
 #include "odb.h"
 #include "oidmap.h"
+#include "array.h"
 
 #define GIT_PACK_FILE_MODE 0444
 
@@ -60,6 +61,14 @@ typedef struct git_pack_cache_entry {
 	git_rawobj raw;
 } git_pack_cache_entry;
 
+struct pack_chain_elem {
+	git_off_t offset;
+	size_t size;
+	git_otype type;
+};
+
+typedef git_array_t(struct pack_chain_elem) git_dependency_chain;
+
 #include "offmap.h"
 
 GIT__USE_OFFMAP;