Introduce Warm-up Phase for Dudect Measurement

Inspired by 'Reparaz et al.'s' 2016 paper, this change adds a
warm-up phase to the function that collects and processes
measurement batches, skipping the first batch to reduce timing
variance in queue operations like insert and remove. Unlike the
author's implementation, which uses dynamic percentile checks,
this approach uses a static boolean to mark the initial run,
suiting the fixed test loop. Experiments in simulation mode with
qtest.c and perf show a minor 1.5% reduction in standard deviation
(from 449ms to 442ms), suggesting a small improvement in execution
stability.

Reference: 'Reparaz et al.', "Dude, is my code constant time?", 2016,
https://eprint.iacr.org/2016/1123.pdf

Change-Id: I71692702401c130cd7cac1d424209308baecb87b

Author: HeatCrab

dudect/fixture.c

@@ -196,8 +196,20 @@ static bool doit(int mode)
     bool ret = measure(before_ticks, after_ticks, input_data, mode);
     differentiate(exec_times, before_ticks, after_ticks);
     prepare_percentiles(exec_times, percentiles);
-    update_statistics(exec_times, classes, percentiles);
-    ret &= report();
+
+    /* This warm-up step discards the first measurement batch by skipping
+     * its statistical analysis. A static boolean flag controls this by
+     * marking the initial execution, ensuring only the first call within
+     * a test run is excluded from the t-test computation.
+     */
+    static bool first_time = true;
+    if (first_time) {
+        first_time = false;
+        ret = true;
+    } else {
+        update_statistics(exec_times, classes, percentiles);
+        ret &= report();
+    }
 
     free(before_ticks);
     free(after_ticks);