Add a macro DIFF_QUEUE_CLEAR.

Refactor the diff_queue_struct code, this macro help
to reset the structure.

Signed-off-by: Bo Yang <struggleyb.nku@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff.c

@@ -2540,6 +2540,7 @@ static void run_checkdiff(struct diff_filepair *p, struct diff_options *o)
 void diff_setup(struct diff_options *options)
 {
 	memset(options, 0, sizeof(*options));
+	memset(&diff_queued_diff, 0, sizeof(diff_queued_diff));
 
 	options->file = stdout;
 
@@ -3457,8 +3458,7 @@ int diff_flush_patch_id(struct diff_options *options, unsigned char *sha1)
 		diff_free_filepair(q->queue[i]);
 
 	free(q->queue);
-	q->queue = NULL;
-	q->nr = q->alloc = 0;
+	DIFF_QUEUE_CLEAR(q);
 
 	return result;
 }
@@ -3586,8 +3586,7 @@ void diff_flush(struct diff_options *options)
 		diff_free_filepair(q->queue[i]);
 free_queue:
 	free(q->queue);
-	q->queue = NULL;
-	q->nr = q->alloc = 0;
+	DIFF_QUEUE_CLEAR(q);
 	if (options->close_file)
 		fclose(options->file);
 
@@ -3609,8 +3608,7 @@ static void diffcore_apply_filter(const char *filter)
 	int i;
 	struct diff_queue_struct *q = &diff_queued_diff;
 	struct diff_queue_struct outq;
-	outq.queue = NULL;
-	outq.nr = outq.alloc = 0;
+	DIFF_QUEUE_CLEAR(&outq);
 
 	if (!filter)
 		return;
@@ -3678,8 +3676,7 @@ static void diffcore_skip_stat_unmatch(struct diff_options *diffopt)
 	int i;
 	struct diff_queue_struct *q = &diff_queued_diff;
 	struct diff_queue_struct outq;
-	outq.queue = NULL;
-	outq.nr = outq.alloc = 0;
+	DIFF_QUEUE_CLEAR(&outq);
 
 	for (i = 0; i < q->nr; i++) {
 		struct diff_filepair *p = q->queue[i];

diffcore-break.c

@@ -162,8 +162,7 @@ void diffcore_break(int break_score)
 	if (!merge_score)
 		merge_score = DEFAULT_MERGE_SCORE;
 
-	outq.nr = outq.alloc = 0;
-	outq.queue = NULL;
+	DIFF_QUEUE_CLEAR(&outq);
 
 	for (i = 0; i < q->nr; i++) {
 		struct diff_filepair *p = q->queue[i];
@@ -256,8 +255,7 @@ void diffcore_merge_broken(void)
 	struct diff_queue_struct outq;
 	int i, j;
 
-	outq.nr = outq.alloc = 0;
-	outq.queue = NULL;
+	DIFF_QUEUE_CLEAR(&outq);
 
 	for (i = 0; i < q->nr; i++) {
 		struct diff_filepair *p = q->queue[i];

diffcore-pickaxe.c

@@ -55,8 +55,7 @@ void diffcore_pickaxe(const char *needle, int opts)
 	int i, has_changes;
 	regex_t regex, *regexp = NULL;
 	struct diff_queue_struct outq;
-	outq.queue = NULL;
-	outq.nr = outq.alloc = 0;
+	DIFF_QUEUE_CLEAR(&outq);
 
 	if (opts & DIFF_PICKAXE_REGEX) {
 		int err;

diffcore-rename.c

@@ -569,8 +569,7 @@ void diffcore_rename(struct diff_options *options)
 	/* At this point, we have found some renames and copies and they
 	 * are recorded in rename_dst.  The original list is still in *q.
 	 */
-	outq.queue = NULL;
-	outq.nr = outq.alloc = 0;
+	DIFF_QUEUE_CLEAR(&outq);
 	for (i = 0; i < q->nr; i++) {
 		struct diff_filepair *p = q->queue[i];
 		struct diff_filepair *pair_to_free = NULL;

diffcore.h

@@ -92,6 +92,11 @@ struct diff_queue_struct {
 	int alloc;
 	int nr;
 };
+#define DIFF_QUEUE_CLEAR(q) \
+	do { \
+		(q)->queue = NULL; \
+		(q)->nr = (q)->alloc = 0; \
+	} while(0);
 
 extern struct diff_queue_struct diff_queued_diff;
 extern struct diff_filepair *diff_queue(struct diff_queue_struct *,