Use time_t instead of long and double for storing uptime

Fixes #275.

This results in fewer casts and less subtraction than the previous
method, and should still be portable. Only division and subtraction and
difftime are performed on the value, so it will not overflow. And the
TCP timestamp itself is a 32-bit value, so it can't refer to a time
farther in the past than the 32-bit epoch. One explicit cast (to long
long) is used in order to ensure the format string can handle any
conceivable value according to the compiler and avoid a warning message.

osscan2.cc

@@ -2551,7 +2551,7 @@ void HostOsScan::makeTSeqFP(HostOsScanStats *hss) {
      5) Same with ~100/sec
   */
   if (hss->si.ts_seqclass == TS_SEQ_UNKNOWN && hss->si.responses >= 2) {
-    double lastboot = 0.0;
+    time_t uptime = 0;
     avg_ts_hz = 0.0;
     for (i = 0; i < hss->si.responses - 1; i++) {
       double dhz;
@@ -2563,31 +2563,33 @@ void HostOsScan::makeTSeqFP(HostOsScanStats *hss) {
 
     if (avg_ts_hz > 0 && avg_ts_hz < 5.66) { /* relatively wide range because sampling time so short and frequency so slow */
       hss->si.ts_seqclass = TS_SEQ_2HZ;
-      lastboot = (double) hss->seq_send_times[0].tv_sec - (hss->si.timestamps[0] / 2);
+      uptime = hss->si.timestamps[0] / 2;
-      hss->si.lastboot = hss->seq_send_times[0].tv_sec - (hss->si.timestamps[0] / 2);
     }
     else if (avg_ts_hz > 70 && avg_ts_hz < 150) {
       hss->si.ts_seqclass = TS_SEQ_100HZ;
-      lastboot = (double) hss->seq_send_times[0].tv_sec - (hss->si.timestamps[0] / 100);
+      uptime = hss->si.timestamps[0] / 100;
     }
     else if (avg_ts_hz > 724 && avg_ts_hz < 1448) {
       hss->si.ts_seqclass = TS_SEQ_1000HZ;
-      lastboot = (double) hss->seq_send_times[0].tv_sec - (hss->si.timestamps[0] / 1000);
+      uptime = hss->si.timestamps[0] / 1000;
     }
     else if (avg_ts_hz > 0) {
       hss->si.ts_seqclass = TS_SEQ_OTHER_NUM;
-      lastboot = (double) hss->seq_send_times[0].tv_sec - (hss->si.timestamps[0] / (unsigned int)(0.5 + avg_ts_hz));
+      uptime = hss->si.timestamps[0] / (unsigned int)(0.5 + avg_ts_hz);
     }
 
-    if (lastboot != 0.0 && (hss->seq_send_times[0].tv_sec - lastboot > 63072000)) {
+    if (uptime > 63072000) {
       /* Up 2 years?  Perhaps, but they're probably lying. */
       if (o.debugging) {
-        log_write(LOG_STDOUT, "Ignoring claimed %s uptime of %lu days\n",
+        /* long long is probably excessive for number of days, but sick of
-        hss->target->targetipstr(), (hss->seq_send_times[0].tv_sec - hss->si.lastboot) / 86400);
+         * truncation warnings and finding the right format string for time_t
+         */
+        log_write(LOG_STDOUT, "Ignoring claimed %s uptime of %lld days\n",
+        hss->target->targetipstr(), (long long) (uptime / 86400));
       }
-      lastboot = 0;
+      uptime = 0;
     }
-    hss->si.lastboot = (long) lastboot;
+    hss->si.lastboot = hss->seq_send_times[0].tv_sec - uptime;
   }
 
   switch (hss->si.ts_seqclass) {

osscan2.h

@@ -200,7 +200,7 @@ struct seq_info {
   u32 timestamps[NUM_SEQ_SAMPLES];
   int index;
   u16 ipids[NUM_SEQ_SAMPLES];
-  long lastboot; /* 0 means unknown */
+  time_t lastboot; /* 0 means unknown */
 };
 
 /* Different kinds of Ipids. */

output.cc

@@ -1989,17 +1989,17 @@ void printosscanoutput(Target *currenths) {
   if (currenths->seq.lastboot) {
     char tmbuf[128];
     struct timeval tv;
-    time_t lastboot;
+    double uptime;
-    lastboot = (time_t) currenths->seq.lastboot;
+    strncpy(tmbuf, ctime(&currenths->seq.lastboot), sizeof(tmbuf));
-    strncpy(tmbuf, ctime(&lastboot), sizeof(tmbuf));
     chomp(tmbuf);
     gettimeofday(&tv, NULL);
+    uptime = difftime(tv.tv_sec, currenths->seq.lastboot);
     if (o.verbose)
       log_write(LOG_PLAIN, "Uptime guess: %.3f days (since %s)\n",
-                (double) (tv.tv_sec - currenths->seq.lastboot) / 86400,
+                uptime / 86400,
                 tmbuf);
     xml_open_start_tag("uptime");
-    xml_attribute("seconds", "%li", tv.tv_sec - currenths->seq.lastboot);
+    xml_attribute("seconds", "%.0f", uptime);
     xml_attribute("lastboot", "%s", tmbuf);
     xml_close_empty_tag();
     xml_newline();