--- /dev/null
+/*
+ * Copyright (C) the libgit2 contributors. All rights reserved.
+ *
+ * This file is part of libgit2, distributed under the GNU GPL v2 with
+ * a Linking Exception. For full terms see the included COPYING file.
+ */
+
+#ifndef INCLUDE_commit_graph_h__
+#define INCLUDE_commit_graph_h__
+
+#include "common.h"
+
+#include "git2/types.h"
+#include "git2/sys/commit_graph.h"
+
+#include "map.h"
+#include "vector.h"
+#include "oid.h"
+#include "hash.h"
+
+/**
+ * A commit-graph file.
+ *
+ * This file contains metadata about commits, particularly the generation
+ * number for each one. This can help speed up graph operations without
+ * requiring a full graph traversal.
+ *
+ * Support for this feature was added in git 2.19.
+ */
+typedef struct git_commit_graph_file {
+ git_map graph_map;
+
+ /* The OID Fanout table. */
+ const uint32_t *oid_fanout;
+ /* The total number of commits in the graph. */
+ uint32_t num_commits;
+
+ /* The OID Lookup table. */
+ unsigned char *oid_lookup;
+
+ /*
+ * The Commit Data table. Each entry contains the OID of the commit followed
+ * by two 8-byte fields in network byte order:
+ * - The indices of the first two parents (32 bits each).
+ * - The generation number (first 30 bits) and commit time in seconds since
+ * UNIX epoch (34 bits).
+ */
+ const unsigned char *commit_data;
+
+ /*
+ * The Extra Edge List table. Each 4-byte entry is a network byte order index
+ * of one of the i-th (i > 0) parents of commits in the `commit_data` table,
+ * when the commit has more than 2 parents.
+ */
+ const unsigned char *extra_edge_list;
+ /* The number of entries in the Extra Edge List table. Each entry is 4 bytes wide. */
+ size_t num_extra_edge_list;
+
+ /* The trailer of the file. Contains the SHA1-checksum of the whole file. */
+ unsigned char checksum[GIT_HASH_SHA1_SIZE];
+} git_commit_graph_file;
+
+/**
+ * An entry in the commit-graph file. Provides a subset of the information that
+ * can be obtained from the commit header.
+ */
+typedef struct git_commit_graph_entry {
+ /* The generation number of the commit within the graph */
+ size_t generation;
+
+ /* Time in seconds from UNIX epoch. */
+ git_time_t commit_time;
+
+ /* The number of parents of the commit. */
+ size_t parent_count;
+
+ /*
+ * The indices of the parent commits within the Commit Data table. The value
+ * of `GIT_COMMIT_GRAPH_MISSING_PARENT` indicates that no parent is in that
+ * position.
+ */
+ size_t parent_indices[2];
+
+ /* The index within the Extra Edge List of any parent after the first two. */
+ size_t extra_parents_index;
+
+ /* The SHA-1 hash of the root tree of the commit. */
+ git_oid tree_oid;
+
+ /* The SHA-1 hash of the requested commit. */
+ git_oid sha1;
+} git_commit_graph_entry;
+
+/* A wrapper for git_commit_graph_file to enable lazy loading in the ODB. */
+struct git_commit_graph {
+ /* The path to the commit-graph file. Something like ".git/objects/info/commit-graph". */
+ git_str filename;
+
+ /* The underlying commit-graph file. */
+ git_commit_graph_file *file;
+
+ /* Whether the commit-graph file was already checked for validity. */
+ bool checked;
+};
+
+/** Create a new commit-graph, optionally opening the underlying file. */
+int git_commit_graph_new(git_commit_graph **cgraph_out, const char *objects_dir, bool open_file);
+
+/** Open and validate a commit-graph file. */
+int git_commit_graph_file_open(git_commit_graph_file **file_out, const char *path);
+
+/*
+ * Attempt to get the git_commit_graph's commit-graph file. This object is
+ * still owned by the git_commit_graph. If the repository does not contain a commit graph,
+ * it will return GIT_ENOTFOUND.
+ *
+ * This function is not thread-safe.
+ */
+int git_commit_graph_get_file(git_commit_graph_file **file_out, git_commit_graph *cgraph);
+
+/* Marks the commit-graph file as needing a refresh. */
+void git_commit_graph_refresh(git_commit_graph *cgraph);
+
+/*
+ * A writer for `commit-graph` files.
+ */
+struct git_commit_graph_writer {
+ /*
+ * The path of the `objects/info` directory where the `commit-graph` will be
+ * stored.
+ */
+ git_str objects_info_dir;
+
+ /* The list of packed commits. */
+ git_vector commits;
+};
+
+int git_commit_graph__writer_dump(
+ git_str *cgraph,
+ git_commit_graph_writer *w,
+ git_commit_graph_writer_options *opts);
+
+/*
+ * Returns whether the git_commit_graph_file needs to be reloaded since the
+ * contents of the commit-graph file have changed on disk.
+ */
+bool git_commit_graph_file_needs_refresh(
+ const git_commit_graph_file *file, const char *path);
+
+int git_commit_graph_entry_find(
+ git_commit_graph_entry *e,
+ const git_commit_graph_file *file,
+ const git_oid *short_oid,
+ size_t len);
+int git_commit_graph_entry_parent(
+ git_commit_graph_entry *parent,
+ const git_commit_graph_file *file,
+ const git_commit_graph_entry *entry,
+ size_t n);
+int git_commit_graph_file_close(git_commit_graph_file *cgraph);
+void git_commit_graph_file_free(git_commit_graph_file *cgraph);
+
+/* This is exposed for use in the fuzzers. */
+int git_commit_graph_file_parse(
+ git_commit_graph_file *file,
+ const unsigned char *data,
+ size_t size);
+
+#endif
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