Optimize calculation of max_t and max_tau

Previously, 'max_t' and 'max_tau' were computed before verifying if the
measurement was sufficient. This change moves their calculation to a
later stage, reducing unnecessary computations when the measurement is
insufficient.

Change-Id: Ifa3afbe308e5a1c40c87ec1b4d9b3362c4c20f04

Author: BennyWang1007

Diff for: dudect/fixture.c

@@ -139,9 +139,7 @@ static t_context_t *max_test()
 static bool report(void)
 {
     t_context_t *t = max_test();
-    double max_t = fabs(t_compute(t));
     double number_traces_max_t = t->n[0] + t->n[1];
-    double max_tau = max_t / sqrt(number_traces_max_t);
 
     printf("\033[A\033[2K");
     printf("measure: %7.2lf M, ", (number_traces_max_t / 1e6));
@@ -151,6 +149,9 @@ static bool report(void)
         return false;
     }
 
+    double max_t = fabs(t_compute(t));
+    double max_tau = max_t / sqrt(number_traces_max_t);
+
     /* max_t: the t statistic value
      * max_tau: a t value normalized by sqrt(number of measurements).
      *          this way we can compare max_tau taken with different