2 files changed, 46 insertions, 0 deletions
diff --git a/src/common/utils.c b/src/common/utils.c
index dcf0a749a..73df3aae1 100644
--- a/src/common/utils.c
+++ b/src/common/utils.c
@@ -25,6 +25,7 @@
 #include "common/cbasetypes.h"
 #include "common/core.h"
 #include "common/mmo.h"
+#include "common/nullpo.h"
 #include "common/showmsg.h"
 #include "common/socket.h"
 #include "common/strlib.h"
@@ -352,6 +353,48 @@ unsigned int get_percentage(const unsigned int A, const unsigned int B)
 	return (unsigned int)floor(result);
 }
 
+/**
+ * Applies a percentual rate modifier.
+ *
+ * @param value The base value.
+ * @param rate  The rate modifier to apply.
+ * @param stdrate The rate modifier's divider (rate == stdrate => 100%).
+ * @return The modified value.
+ */
+int64 apply_percentrate64(int64 value, int rate, int stdrate)
+{
+	Assert_ret(stdrate > 0);
+	Assert_ret(rate >= 0);
+	if (rate == stdrate)
+		return value;
+	if (rate == 0)
+		return 0;
+	if (INT64_MAX / rate < value) {
+		// Give up some precision to prevent overflows
+		return value / stdrate * rate;
+	}
+	return value * rate / stdrate;
+}
+
+/**
+ * Applies a percentual rate modifier.
+ *
+ * @param value The base value.
+ * @param rate  The rate modifier to apply. Must be <= maxrate.
+ * @param maxrate The rate modifier's divider (maxrate = 100%).
+ * @return The modified value.
+ */
+int apply_percentrate(int value, int rate, int maxrate)
+{
+	Assert_ret(maxrate > 0);
+	Assert_ret(rate >= 0);
+	if (rate == maxrate)
+		return value;
+	if (rate == 0)
+		return 0;
+	return (int)(value * (int64)rate / maxrate);
+}
+
 //-----------------------------------------------------
 // custom timestamp formatting (from eApp)
 //-----------------------------------------------------
diff --git a/src/common/utils.h b/src/common/utils.h
index da2a29317..3f181ef12 100644
--- a/src/common/utils.h
+++ b/src/common/utils.h
@@ -42,6 +42,9 @@ bool exists(const char* filename);
 /// calculates the value of A / B, in percent (rounded down)
 unsigned int get_percentage(const unsigned int A, const unsigned int B);
 
+int64 apply_percentrate64(int64 value, int rate, int maxrate);
+int apply_percentrate(int value, int rate, int maxrate);
+
 const char* timestamp2string(char* str, size_t size, time_t timestamp, const char* format);
 
 //////////////////////////////////////////////////////////////////////////