Make our overflow check look more like gcc/clang's

Make our overflow checking look more like gcc and clang's, so that
we can substitute it out with the compiler instrinsics on platforms
that support it.  This means dropping the ability to pass `NULL` as
an out parameter.

As a result, the macros also get updated to reflect this as well.

1 files changed, 7 insertions, 11 deletions

diff --git a/src/tree.c b/src/tree.c
index 573e56447..9fd4e0a07 100644
--- a/src/tree.c
+++ b/src/tree.c
@@ -84,12 +84,11 @@ int git_tree_entry_icmp(const git_tree_entry *e1, const git_tree_entry *e2)
 static git_tree_entry *alloc_entry(const char *filename)
 {
 	git_tree_entry *entry = NULL;
-	size_t filename_len = strlen(filename),
-		tree_len = sizeof(git_tree_entry);
+	size_t filename_len = strlen(filename), tree_len;
 
-	if (GIT_ALLOC_OVERFLOW_ADD(tree_len, filename_len) ||
-		GIT_ALLOC_OVERFLOW_ADD(tree_len + filename_len, 1) ||
-		!(entry = git__malloc(tree_len + filename_len + 1)))
+	if (GIT_ADD_SIZET_OVERFLOW(&tree_len, sizeof(git_tree_entry), filename_len) ||
+		GIT_ADD_SIZET_OVERFLOW(&tree_len, tree_len, 1) ||
+		!(entry = git__malloc(tree_len)))
 		return NULL;
 
 	memset(entry, 0x0, sizeof(git_tree_entry));
@@ -207,16 +206,13 @@ void git_tree_entry_free(git_tree_entry *entry)
 
 int git_tree_entry_dup(git_tree_entry **dest, const git_tree_entry *source)
 {
-	size_t total_size = sizeof(git_tree_entry);
+	size_t total_size;
 	git_tree_entry *copy;
 
 	assert(source);
 
-	GITERR_CHECK_ALLOC_ADD(total_size, source->filename_len);
-	total_size += source->filename_len;
-
-	GITERR_CHECK_ALLOC_ADD(total_size, 1);
-	total_size++;
+	GITERR_CHECK_ALLOC_ADD(&total_size, sizeof(git_tree_entry), source->filename_len);
+	GITERR_CHECK_ALLOC_ADD(&total_size, total_size, 1);
 
 	copy = git__malloc(total_size);
 	GITERR_CHECK_ALLOC(copy);