Add some more type checking.

NOTE: This commit breaks the build, because there was a mistake in an
earlier change of exactly the sort that this is meant to detect!  I'm
leaving it broken for illustration.

3 files changed, 37 insertions, 17 deletions

diff --git a/src/core/or/circuitpadding.c b/src/core/or/circuitpadding.c
index a5d5d24551..4080614338 100644
--- a/src/core/or/circuitpadding.c
+++ b/src/core/or/circuitpadding.c
@@ -541,7 +541,7 @@ circpad_distribution_sample(circpad_distribution_t dist)
       {
         // param2 is upper bound, param1 is lower
         const struct uniform my_uniform = {
-          .base = DIST_BASE(&uniform_ops),
+          .base = UNIFORM(my_uniform),
           .a = dist.param1,
           .b = dist.param2,
         };
@@ -551,7 +551,7 @@ circpad_distribution_sample(circpad_distribution_t dist)
       {
       /* param1 is Mu, param2 is sigma. */
         const struct logistic my_logistic = {
-          .base = DIST_BASE(&uniform_ops),
+          .base = LOGISTIC(my_uniform),
           .mu = dist.param1,
           .sigma = dist.param2,
         };
@@ -561,7 +561,7 @@ circpad_distribution_sample(circpad_distribution_t dist)
       {
         /* param1 is Alpha, param2 is 1.0/Beta */
         const struct log_logistic my_log_logistic = {
-          .base = DIST_BASE(&log_logistic_ops),
+          .base = LOG_LOGISTIC(my_log_logistic),
           .alpha = dist.param1,
           .beta = dist.param2,
         };
@@ -571,7 +571,7 @@ circpad_distribution_sample(circpad_distribution_t dist)
       {
         /* param1 is 'p' (success probability) */
         const struct geometric my_geometric = {
-          .base = DIST_BASE(&geometric_ops),
+          .base = GEOMETRIC(my_geometric),
           .p = dist.param1,
         };
         return dist_sample(&my_geometric.base);
@@ -580,7 +580,7 @@ circpad_distribution_sample(circpad_distribution_t dist)
       {
         /* param1 is k, param2 is Lambda */
         const struct weibull my_weibull = {
-          .base = DIST_BASE(&weibull_ops),
+          .base = WEIBULL(my_weibull),
           .k = dist.param1,
           .lambda = dist.param2,
         };
@@ -590,7 +590,7 @@ circpad_distribution_sample(circpad_distribution_t dist)
       {
         /* param1 is sigma, param2 is xi, no more params for mu so we use 0 */
         const struct genpareto my_genpareto = {
-          .base = DIST_BASE(&weibull_ops),
+          .base = GENPARETO(my_weibull),
           .mu = 0,
           .sigma = dist.param1,
           .xi = dist.param2,
diff --git a/src/lib/math/prob_distr.h b/src/lib/math/prob_distr.h
index 981fc2017d..66acb796fd 100644
--- a/src/lib/math/prob_distr.h
+++ b/src/lib/math/prob_distr.h
@@ -20,6 +20,8 @@ struct dist {
 };
 
 #define DIST_BASE(OPS)  { .ops = (OPS) }
+#define DIST_BASE_TYPED(OPS, OBJ, TYPE)                         \
+  DIST_BASE((OPS) + 0*sizeof(&(OBJ) - (const TYPE *)&(OBJ)))
 
 const char *dist_name(const struct dist *);
 double dist_sample(const struct dist *);
@@ -46,6 +48,9 @@ struct geometric {
 
 extern const struct dist_ops geometric_ops;
 
+#define GEOMETRIC(OBJ)                                      \
+  DIST_BASE_TYPED(&geometric_ops, OBJ, struct geometric)
+
 /* Pareto distribution */
 
 struct genpareto {
@@ -57,6 +62,9 @@ struct genpareto {
 
 extern const struct dist_ops genpareto_ops;
 
+#define GENPARETO(OBJ)                                      \
+  DIST_BASE_TYPED(&genpareto_ops, OBJ, struct genpareto)
+
 /* Weibull distribution */
 
 struct weibull {
@@ -67,6 +75,9 @@ struct weibull {
 
 extern const struct dist_ops weibull_ops;
 
+#define WEIBULL(OBJ)                                    \
+  DIST_BASE_TYPED(&weibull_ops, OBJ, struct weibull)
+
 /* Log-logistic distribution */
 
 struct log_logistic {
@@ -77,6 +88,9 @@ struct log_logistic {
 
 extern const struct dist_ops log_logistic_ops;
 
+#define LOG_LOGISTIC(OBJ)                                       \
+  DIST_BASE_TYPED(&log_logistic_ops, OBJ, struct log_logistic)
+
 /* Logistic distribution */
 
 struct logistic {
@@ -87,6 +101,9 @@ struct logistic {
 
 extern const struct dist_ops logistic_ops;
 
+#define LOGISTIC(OBJ)                                   \
+  DIST_BASE_TYPED(&logistic_ops, OBJ, struct logistic)
+
 /* Uniform distribution */
 
 struct uniform {
@@ -97,6 +114,9 @@ struct uniform {
 
 extern const struct dist_ops uniform_ops;
 
+#define UNIFORM(OBJ)                                    \
+  DIST_BASE_TYPED(&uniform_ops, OBJ, struct uniform)
+
 /** Only by unittests */
 
 #ifdef PROB_DISTR_PRIVATE
diff --git a/src/test/test_prob_distr.c b/src/test/test_prob_distr.c
index fe3969518c..ff23f01033 100644
--- a/src/test/test_prob_distr.c
+++ b/src/test/test_prob_distr.c
@@ -943,7 +943,7 @@ static bool
 test_stochastic_geometric_impl(double p)
 {
   const struct geometric geometric = {
-    .base = DIST_BASE(&geometric_ops),
+    .base = GEOMETRIC(geometric),
     .p = p,
   };
   double logP[PSI_DF] = {0};
@@ -1151,32 +1151,32 @@ test_stochastic_uniform(void *arg)
   (void) arg;
 
   const struct uniform uniform01 = {
-    .base = DIST_BASE(&uniform_ops),
+    .base = UNIFORM(uniform01),
     .a = 0,
     .b = 1,
   };
   const struct uniform uniform_pos = {
-    .base = DIST_BASE(&uniform_ops),
+    .base = UNIFORM(uniform_pos),
     .a = 1.23,
     .b = 4.56,
   };
   const struct uniform uniform_neg = {
-    .base = DIST_BASE(&uniform_ops),
+    .base = UNIFORM(uniform_neg),
     .a = -10,
     .b = -1,
   };
   const struct uniform uniform_cross = {
-    .base = DIST_BASE(&uniform_ops),
+    .base = UNIFORM(uniform_cross),
     .a = -1.23,
     .b = 4.56,
   };
   const struct uniform uniform_subnormal = {
-    .base = DIST_BASE(&uniform_ops),
+    .base = UNIFORM(uniform_subnormal),
     .a = 4e-324,
     .b = 4e-310,
   };
   const struct uniform uniform_subnormal_cross = {
-    .base = DIST_BASE(&uniform_ops),
+    .base = UNIFORM(uniform_subnormal_cross),
     .a = -4e-324,
     .b = 4e-310,
   };
@@ -1202,7 +1202,7 @@ static bool
 test_stochastic_logistic_impl(double mu, double sigma)
 {
   const struct logistic dist = {
-    .base = DIST_BASE(&logistic_ops),
+    .base = LOGISTIC(dist),
     .mu = mu,
     .sigma = sigma,
   };
@@ -1215,7 +1215,7 @@ static bool
 test_stochastic_log_logistic_impl(double alpha, double beta)
 {
   const struct log_logistic dist = {
-    .base = DIST_BASE(&log_logistic_ops),
+    .base = LOG_LOGISTIC(dist),
     .alpha = alpha,
     .beta = beta,
   };
@@ -1228,7 +1228,7 @@ static bool
 test_stochastic_weibull_impl(double lambda, double k)
 {
   const struct weibull dist = {
-    .base = DIST_BASE(&weibull_ops),
+    .base = WEIBULL(dist),
     .lambda = lambda,
     .k = k,
   };
@@ -1248,7 +1248,7 @@ static bool
 test_stochastic_genpareto_impl(double mu, double sigma, double xi)
 {
   const struct genpareto dist = {
-    .base = DIST_BASE(&genpareto_ops),
+    .base = GENPARETO(dist),
     .mu = mu,
     .sigma = sigma,
     .xi = xi,