Fix dist_min_usec documentation and naming.

src/core/or/circuitpadding.c

@@ -380,17 +380,17 @@ circpad_choose_state_length(circpad_machine_state_t *mi)
  */
 static circpad_delay_t
 circpad_distribution_sample_iat_delay(const circpad_state_t *state,
-                                      circpad_delay_t min_delay)
+                                      circpad_delay_t delay_shift)
 {
   double val = circpad_distribution_sample(state->iat_dist);
   /* These comparisons are safe, because the output is in the range
    * [0, 2**32), and double has a precision of 53 bits. */
   val = MAX(0, val);
-  val = MIN(val, state->dist_max_usec);
+  val = MIN(val, state->dist_max_sample_usec);
 
   /* This addition is exact: val is at most 2**32-1, min_delay
    * is at most 2**32-1, and doubles have a precision of 53 bits. */
-  val += min_delay;
+  val += delay_shift;
 
   /* Clamp the distribution at infinite delay val */
   return (circpad_delay_t)MIN(tor_llround(val), CIRCPAD_DELAY_INFINITE);
@@ -420,9 +420,10 @@ circpad_machine_sample_delay(circpad_machine_state_t *mi)
 
   if (state->iat_dist.type != CIRCPAD_DIST_NONE) {
     /* Sample from a fixed IAT distribution and return */
-    circpad_delay_t min_iat_delay = state->use_rtt_estimate ?
-      mi->rtt_estimate_usec + state->dist_min_usec : state->dist_min_usec;
-    return circpad_distribution_sample_iat_delay(state, min_iat_delay);
+    circpad_delay_t iat_delay_shift = state->use_rtt_estimate ?
+      mi->rtt_estimate_usec + state->dist_added_shift_usec :
+      state->dist_added_shift_usec;
+    return circpad_distribution_sample_iat_delay(state, iat_delay_shift);
   } else if (state->token_removal != CIRCPAD_TOKEN_REMOVAL_NONE) {
     /* We have a mutable histogram. Do basic sanity check and apply: */
     if (BUG(!mi->histogram) ||

src/core/or/circuitpadding.h

@@ -309,13 +309,16 @@ typedef struct circpad_state_t {
    * results of sampling from this distribution (range_sec is used as a max).
    */
   circpad_distribution_t iat_dist;
-  /*  If a delay probability distribution is used, this represents the minimum
-   *  delay we can sample from the distribution. */
-  circpad_delay_t dist_min_usec;
   /*  If a delay probability distribution is used, this is used as the max
-   *  delay we can sample from the distribution.
-   */
-  circpad_delay_t dist_max_usec;
+   *  value we can sample from the distribution. However, RTT measurements and
+   *  dist_added_shift gets applied on top of this value to derive the final
+   *  padding delay. */
+  circpad_delay_t dist_max_sample_usec;
+  /*  If a delay probability distribution is used and this is set, we will add
+   *  this value on top of the value sampled from the IAT distribution to
+   *  derive the final padding delay (We also add the RTT measurement if it's
+   *  enabled.). */
+  circpad_delay_t dist_added_shift_usec;
 
   /**
    * The length dist is a parameterized way of encoding how long this

src/test/test_circuitpadding.c

@@ -2098,48 +2098,48 @@ helper_circpad_circ_distribution_machine_setup(int min, int max)
   zero_st->iat_dist.type = CIRCPAD_DIST_UNIFORM;
   zero_st->iat_dist.param1 = min;
   zero_st->iat_dist.param2 = max;
-  zero_st->dist_min_usec = min;
-  zero_st->dist_max_usec = max;
+  zero_st->dist_added_shift_usec = min;
+  zero_st->dist_max_sample_usec = max;
 
   circpad_state_t *first_st = &circ_client_machine.states[1];
   first_st->next_state[CIRCPAD_EVENT_NONPADDING_RECV] = 2;
   first_st->iat_dist.type = CIRCPAD_DIST_LOGISTIC;
   first_st->iat_dist.param1 = min;
   first_st->iat_dist.param2 = max;
-  first_st->dist_min_usec = min;
-  first_st->dist_max_usec = max;
+  first_st->dist_added_shift_usec = min;
+  first_st->dist_max_sample_usec = max;
 
   circpad_state_t *second_st = &circ_client_machine.states[2];
   second_st->next_state[CIRCPAD_EVENT_NONPADDING_RECV] = 3;
   second_st->iat_dist.type = CIRCPAD_DIST_LOG_LOGISTIC;
   second_st->iat_dist.param1 = min;
   second_st->iat_dist.param2 = max;
-  second_st->dist_min_usec = min;
-  second_st->dist_max_usec = max;
+  second_st->dist_added_shift_usec = min;
+  second_st->dist_max_sample_usec = max;
 
   circpad_state_t *third_st = &circ_client_machine.states[3];
   third_st->next_state[CIRCPAD_EVENT_NONPADDING_RECV] = 4;
   third_st->iat_dist.type = CIRCPAD_DIST_GEOMETRIC;
   third_st->iat_dist.param1 = min;
   third_st->iat_dist.param2 = max;
-  third_st->dist_min_usec = min;
-  third_st->dist_max_usec = max;
+  third_st->dist_added_shift_usec = min;
+  third_st->dist_max_sample_usec = max;
 
   circpad_state_t *fourth_st = &circ_client_machine.states[4];
   fourth_st->next_state[CIRCPAD_EVENT_NONPADDING_RECV] = 5;
   fourth_st->iat_dist.type = CIRCPAD_DIST_WEIBULL;
   fourth_st->iat_dist.param1 = min;
   fourth_st->iat_dist.param2 = max;
-  fourth_st->dist_min_usec = min;
-  fourth_st->dist_max_usec = max;
+  fourth_st->dist_added_shift_usec = min;
+  fourth_st->dist_max_sample_usec = max;
 
   circpad_state_t *fifth_st = &circ_client_machine.states[5];
   fifth_st->next_state[CIRCPAD_EVENT_NONPADDING_RECV] = 6;
   fifth_st->iat_dist.type = CIRCPAD_DIST_PARETO;
   fifth_st->iat_dist.param1 = min;
   fifth_st->iat_dist.param2 = max;
-  fifth_st->dist_min_usec = min;
-  fifth_st->dist_max_usec = max;
+  fifth_st->dist_added_shift_usec = min;
+  fifth_st->dist_max_sample_usec = max;
 }
 
 /** Simple test that the padding delays sampled from a uniform distribution