Make difficulty trend correction asymmetric

src/cryptonote_config.h

@@ -301,7 +301,8 @@
 #define DIFFICULTY_TREND_OLDER_WINDOW                   15
 #define DIFFICULTY_TREND_SMOOTHING_NUM                   3
 #define DIFFICULTY_TREND_SMOOTHING_DEN                  10
-#define DIFFICULTY_TREND_MAX_ADJUST_PERCENT              5
+#define DIFFICULTY_TREND_MAX_UP_PERCENT                  3
+#define DIFFICULTY_TREND_MAX_DOWN_PERCENT               10
 
 //The limit is enough for the mandatory transaction content with 16 outputs (547 bytes),
 //a custom tag (1 byte) and up to 32 bytes of custom data for each recipient.

src/cryptonote_core/blockchain.cpp

@@ -191,11 +191,12 @@ namespace
     int64_t adjust_scaled = 10000 +
         (deviation * DIFFICULTY_TREND_SMOOTHING_NUM) / DIFFICULTY_TREND_SMOOTHING_DEN;
 
-    const int64_t max_adjust = DIFFICULTY_TREND_MAX_ADJUST_PERCENT * 100;
-    if (adjust_scaled > 10000 + max_adjust)
-      adjust_scaled = 10000 + max_adjust;
-    if (adjust_scaled < 10000 - max_adjust)
-      adjust_scaled = 10000 - max_adjust;
+    const int64_t max_adjust_up = DIFFICULTY_TREND_MAX_UP_PERCENT * 100;
+    const int64_t max_adjust_down = DIFFICULTY_TREND_MAX_DOWN_PERCENT * 100;
+    if (adjust_scaled > 10000 + max_adjust_up)
+      adjust_scaled = 10000 + max_adjust_up;
+    if (adjust_scaled < 10000 - max_adjust_down)
+      adjust_scaled = 10000 - max_adjust_down;
 
     cryptonote::difficulty_type adjusted = (calculated_difficulty * adjust_scaled) / 10000;
     if (adjusted < 1)