2 files changed, 20 insertions, 50 deletions
diff --git a/source/ui-stats.c b/source/ui-stats.c
index 9c79e74..6b05c80 100644
--- a/source/ui-stats.c
+++ b/source/ui-stats.c
@@ -35,19 +35,11 @@ static void trunc_week(struct tm *tm)
 	gmtime_r(&t, tm);
 }
 
-static void dec_week(struct tm *tm)
+static void step_week(struct tm *tm, int n)
 {
 	time_t t = timegm(tm);
 
-	t -= SECONDS_PER_WEEK;
-	gmtime_r(&t, tm);
-}
-
-static void inc_week(struct tm *tm)
-{
-	time_t t = timegm(tm);
-
-	t += SECONDS_PER_WEEK;
+	t += n * SECONDS_PER_WEEK;
 	gmtime_r(&t, tm);
 }
 
@@ -68,21 +60,15 @@ static void trunc_month(struct tm *tm)
 	tm->tm_mday = 1;
 }
 
-static void dec_month(struct tm *tm)
+static void step_month(struct tm *tm, int n)
 {
-	tm->tm_mon--;
+	tm->tm_mon += n;
 	if (tm->tm_mon < 0) {
 		tm->tm_year--;
-		tm->tm_mon = 11;
-	}
-}
-
-static void inc_month(struct tm *tm)
-{
-	tm->tm_mon++;
-	if (tm->tm_mon > 11) {
+		tm->tm_mon += 12;
+	} else if (tm->tm_mon > 11) {
 		tm->tm_year++;
-		tm->tm_mon = 0;
+		tm->tm_mon -= 12;
 	}
 }
 
@@ -98,22 +84,12 @@ static char *pretty_month(struct tm *tm)
 static void trunc_quarter(struct tm *tm)
 {
 	trunc_month(tm);
-	while (tm->tm_mon % 3 != 0)
-		dec_month(tm);
-}
-
-static void dec_quarter(struct tm *tm)
-{
-	dec_month(tm);
-	dec_month(tm);
-	dec_month(tm);
+	tm->tm_mon -= tm->tm_mon % 3;
 }
 
-static void inc_quarter(struct tm *tm)
+static void step_quarter(struct tm *tm, int n)
 {
-	inc_month(tm);
-	inc_month(tm);
-	inc_month(tm);
+	step_month(tm, 3 * n);
 }
 
 static char *pretty_quarter(struct tm *tm)
@@ -127,14 +103,9 @@ static void trunc_year(struct tm *tm)
 	tm->tm_mon = 0;
 }
 
-static void dec_year(struct tm *tm)
-{
-	tm->tm_year--;
-}
-
-static void inc_year(struct tm *tm)
+static void step_year(struct tm *tm, int n)
 {
-	tm->tm_year++;
+	tm->tm_year += n;
 }
 
 static char *pretty_year(struct tm *tm)
@@ -145,10 +116,10 @@ static char *pretty_year(struct tm *tm)
 // The order runs from the finest window to the coarsest, because a repository
 // caps the page by storing an index into this table as its max-stats.
 static const struct cgit_period periods[] = {
-	{'w', "week", 4, trunc_week, dec_week, inc_week, pretty_week},
-	{'m', "month", 4, trunc_month, dec_month, inc_month, pretty_month},
-	{'q', "quarter", 4, trunc_quarter, dec_quarter, inc_quarter, pretty_quarter},
-	{'y', "year", 4, trunc_year, dec_year, inc_year, pretty_year},
+	{'w', "week", 4, trunc_week, step_week, pretty_week},
+	{'m', "month", 4, trunc_month, step_month, pretty_month},
+	{'q', "quarter", 4, trunc_quarter, step_quarter, pretty_quarter},
+	{'y', "year", 4, trunc_year, step_year, pretty_year},
 };
 
 static void window_start(const struct cgit_period *period, struct tm *tm)
@@ -167,7 +138,7 @@ static void window_start(const struct cgit_period *period, struct tm *tm)
 	tm->tm_min = 0;
 	tm->tm_sec = 0;
 	for (i = 1; i < period->count; i++)
-		period->dec(tm);
+		period->step(tm, -1);
 }
 
 static void add_commit(struct string_list *authors, struct commitinfo *info,
@@ -283,7 +254,7 @@ static struct string_list build_period_labels(const struct cgit_period *period)
 	window_start(period, &tm);
 	for (i = 0; i < period->count; i++) {
 		string_list_append(&labels, period->pretty(&tm));
-		period->inc(&tm);
+		period->step(&tm, 1);
 	}
 	return labels;
 }
diff --git a/source/ui-stats.h b/source/ui-stats.h
index 325e082..1cd0b9d 100644
--- a/source/ui-stats.h
+++ b/source/ui-stats.h
@@ -20,9 +20,8 @@ struct cgit_period {
 	// Move a tm back to the first day of the period it falls in.
 	void (*trunc)(struct tm *tm);
 
-	// Step a truncated tm one whole period back or forward.
-	void (*dec)(struct tm *tm);
-	void (*inc)(struct tm *tm);
+	// Step a truncated tm n whole periods, back when n is negative.
+	void (*step)(struct tm *tm, int n);
 
 	// Label the period a tm falls in. The buffer is reused, so a caller
 	// that keeps a label copies it.