Fix comments from Sebastian + Nick's code review.

Check for overflow in one place, and be consistent about type usage.

src/or/circuitbuild.c

@@ -955,7 +955,7 @@ circuit_build_times_network_check_live(circuit_build_times_t *cbt)
     }
 
     return 0;
-  } else if (cbt->liveness.suspended_timeout) {
+  } else if (cbt->liveness.suspended_timeout > 0) {
     log_notice(LD_CIRC,
               "Network activity has resumed. "
               "Resuming circuit timeout calculations.");
@@ -1004,7 +1004,12 @@ circuit_build_times_network_check_changed(circuit_build_times_t *cbt)
   /* Check to see if this has happened before. If so, double the timeout
    * to give people on abysmally bad network connections a shot at access */
   if (cbt->timeout_ms >= circuit_build_times_get_initial_timeout()) {
-    cbt->timeout_ms *= 2;
+    if (cbt->timeout_ms > INT32_MAX/2) {
+      log_warn(LD_CIRC, "Insanely large circuit build timeout value: %lf",
+               cbt->timeout_ms);
+    } else {
+      cbt->timeout_ms *= 2;
+    }
   } else {
     cbt->timeout_ms = circuit_build_times_get_initial_timeout();
   }
@@ -1100,7 +1105,7 @@ circuit_build_times_filter_timeouts(circuit_build_times_t *cbt)
   }
 
   timeout_rate = circuit_build_times_timeout_rate(cbt);
-  max_timeout = tor_lround(circuit_build_times_calculate_timeout(cbt,
+  max_timeout = (build_time_t)tor_lround(circuit_build_times_calculate_timeout(cbt,
                     circuit_build_times_max_synthetic_quantile()));
 
   for (i = 0; i < CBT_NCIRCUITS_TO_OBSERVE; i++) {

src/or/or.h

@@ -3113,7 +3113,7 @@ typedef struct {
   int after_firsthop_idx;
   /** Timeout gathering is suspended if non-zero. The old timeout value
     * is stored here in that case. */
-  build_time_t suspended_timeout;
+  double suspended_timeout;
 } network_liveness_t;
 
 /** Structure for circuit build times history */
@@ -3137,7 +3137,8 @@ typedef struct {
   double alpha;
   /** Have we computed a timeout? */
   int have_computed_timeout;
-  /** The exact value for that timeout in milliseconds */
+  /** The exact value for that timeout in milliseconds. Stored as a double
+   * to maintain precision from calculations to and from quantile value. */
   double timeout_ms;
 } circuit_build_times_t;