thodg/libgit2

diff --git a/src/common.h b/src/common.h
index 6dca36f..7170df9 100644
--- a/src/common.h
+++ b/src/common.h
@@ -208,6 +208,15 @@ GIT_INLINE(void) git__init_structure(void *structure, size_t len, unsigned int v
 #define GITERR_CHECK_ALLOC_ADD(out, one, two) \
 	if (GIT_ADD_SIZET_OVERFLOW(out, one, two)) { return -1; }
 
+#define GITERR_CHECK_ALLOC_ADD3(out, one, two, three) \
+	if (GIT_ADD_SIZET_OVERFLOW(out, one, two) || \
+		GIT_ADD_SIZET_OVERFLOW(out, *(out), three)) { return -1; }
+
+#define GITERR_CHECK_ALLOC_ADD4(out, one, two, three, four) \
+	if (GIT_ADD_SIZET_OVERFLOW(out, one, two) || \
+		GIT_ADD_SIZET_OVERFLOW(out, *(out), three) || \
+		GIT_ADD_SIZET_OVERFLOW(out, *(out), four)) { return -1; }
+
 /** Check for multiplicative overflow, failing if it would occur. */
 #define GITERR_CHECK_ALLOC_MULTIPLY(out, nelem, elsize) \
 	if (GIT_MULTIPLY_SIZET_OVERFLOW(out, nelem, elsize)) { return -1; }