From: Tobias Jakobi <tjakobi@math.uni-bielefeld.de>
Date: Wed, 1 Feb 2017 20:48:50 +0000 (+0100)
Subject: Use proper 64-bit integer arithmetic for Hz calculation
X-Git-Url: https://iankelling.org/git/?a=commitdiff_plain;h=04261c1142b015c6995a1a635e5e8aa70bf873ca;p=evhz

Use proper 64-bit integer arithmetic for Hz calculation

The current code uses double floats, which makes no sense since
time differences are always integer and never fractional.

Also fix up the averaging code a bit.

This fixes some spurious wrong Hz values reported for
my Logitech Rumblepad 2.

Signed-off-by: Tobias Jakobi <tjakobi@math.uni-bielefeld.de>
---

diff --git a/evhz.c b/evhz.c
index e515ce5..4fd770d 100644
--- a/evhz.c
+++ b/evhz.c
@@ -27,7 +27,7 @@ typedef struct event_s {
     int hz[HZ_LIST];
     int count;
     int avghz;
-    double prev_time;
+    unsigned long long prev_time;
     char name[128];
 } event_t;
 
@@ -115,25 +115,32 @@ int main(int argc, char *argv[]) {
             }
 
             if(event.type == EV_REL || event.type == EV_ABS) {
-                double time;
-                int hz;
+                unsigned long long time, timediff;
+                unsigned hz = 0;
 
-                time = event.time.tv_sec * 1000 + event.time.tv_usec / 1000;
-                hz = 1000 / (time - events[i].prev_time);
+                time = (unsigned long long)event.time.tv_sec * 1000ULL;
+                time += (unsigned long long)event.time.tv_usec / 1000ULL;
+
+                timediff = time - events[i].prev_time;
+
+                if(timediff != 0)
+                    hz = 1000ULL / timediff;
 
                 if(hz > 0) {
-                    int j;
+                    unsigned j, maxavg;
 
                     events[i].count++;
                     events[i].hz[events[i].count & (HZ_LIST - 1)] = hz;
 
                     events[i].avghz = 0;
 
-                    for(j = 0; j < HZ_LIST; j++) {
+                    maxavg = (events[i].count > HZ_LIST) ? HZ_LIST : events[i].count;
+
+                    for(j = 0; j < maxavg; j++) {
                         events[i].avghz += events[i].hz[j];
                     }
 
-                    events[i].avghz /= (events[i].count > HZ_LIST) ? HZ_LIST : events[i].count;
+                    events[i].avghz /= maxavg;
 
                     if(verbose) printf("%s: Latest % 5iHz, Average % 5iHz\n", events[i].name, hz, events[i].avghz);
                 }