From 9ca4a354eede406a4eee5bfbfcf1283a8e6dce90 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Nils=20O=2E=20Sel=C3=A5sdal?= <noselasd@fiane.dyndns.org>
Date: Thu, 10 Oct 2013 01:06:49 +0200
Subject: [PATCH] Fix calculating available tickets. Help prevent overflow when
 there's long periods between calls

---
 src/rate_limit.c | 17 ++++++++++-------
 1 file changed, 10 insertions(+), 7 deletions(-)

diff --git a/src/rate_limit.c b/src/rate_limit.c
index 3ed94bf..fec4c79 100644
--- a/src/rate_limit.c
+++ b/src/rate_limit.c
@@ -1,6 +1,6 @@
 #include "ucore/rate_limit.h"
 
-#define SCALE_FACTOR 1000
+#define SCALE_FACTOR 100
 
 
 void uc_ratelimit_init(struct RateLimit *r, long tickets, long period, long current_ts)
@@ -28,22 +28,25 @@ int uc_ratelimit_allow(struct RateLimit *r, long current_ts)
     //Find elapsed time
     diff_period = current_ts - r->last_ts;
 
-    //If time went backwards, we halt the time for this round
-    if (diff_period < 0) 
+    if (diff_period > r->period + 1) {
+        //help prevent overflow when calculating available_tickets below
+        diff_period = r->period + 1;
+    } else if (diff_period < 0) {
+        //If time went backwards, we halt the time for this round
         diff_period = 0;
+    }
 
     //Calculate the number of tickets that became available since 
-    //the last time. (+ ScALE_FACTOR/2 is to round up at halfway points for
-    //integer arithmetics)
+    //the last time. 
     r->available_tickets += diff_period  * 
-                            ((r->scaled_tickets + SCALE_FACTOR/2) / r->period);
+                            (r->scaled_tickets / r->period);
 
     //throttle handing out tickets
     //
     if (r->available_tickets > r->scaled_tickets) 
         r->available_tickets = r->scaled_tickets;
 
-    //If we have at least onen ticket, we can allow 
+    //If we have at least one ticket, we can allow 
     if (r->available_tickets >=  1 * SCALE_FACTOR) {
         r->available_tickets -= 1 * SCALE_FACTOR;
         allowed = 1;