merge(third_party/git): Merge squashed git subtree at v2.23.0

Merge commit '1b593e1ea4' as 'third_party/git'

third_party/git/commit-slab-decl.h

@@ -0,0 +1,43 @@
+#ifndef COMMIT_SLAB_HDR_H
+#define COMMIT_SLAB_HDR_H
+
+/* allocate ~512kB at once, allowing for malloc overhead */
+#ifndef COMMIT_SLAB_SIZE
+#define COMMIT_SLAB_SIZE (512*1024-32)
+#endif
+
+#define declare_commit_slab(slabname, elemtype) 			\
+									\
+struct slabname {							\
+	unsigned slab_size;						\
+	unsigned stride;						\
+	unsigned slab_count;						\
+	elemtype **slab;						\
+}
+
+/*
+ * Statically initialize a commit slab named "var". Note that this
+ * evaluates "stride" multiple times! Example:
+ *
+ *   struct indegree indegrees = COMMIT_SLAB_INIT(1, indegrees);
+ *
+ */
+#define COMMIT_SLAB_INIT(stride, var) { \
+	COMMIT_SLAB_SIZE / sizeof(**((var).slab)) / (stride), \
+	(stride), 0, NULL \
+}
+
+#define declare_commit_slab_prototypes(slabname, elemtype)		\
+									\
+void init_ ##slabname## _with_stride(struct slabname *s, unsigned stride); \
+void init_ ##slabname(struct slabname *s);				\
+void clear_ ##slabname(struct slabname *s);				\
+elemtype *slabname## _at_peek(struct slabname *s, const struct commit *c, int add_if_missing); \
+elemtype *slabname## _at(struct slabname *s, const struct commit *c);	\
+elemtype *slabname## _peek(struct slabname *s, const struct commit *c)
+
+#define define_shared_commit_slab(slabname, elemtype) \
+	declare_commit_slab(slabname, elemtype); \
+	declare_commit_slab_prototypes(slabname, elemtype)
+
+#endif /* COMMIT_SLAB_HDR_H */