Different order for rng

inst/include/dust2/r/filter.hpp

@@ -174,9 +174,28 @@ cpp11::sexp dust2_cpu_filter_run(cpp11::sexp ptr, cpp11::sexp r_pars,
 template <typename T>
 cpp11::sexp dust2_cpu_filter_rng_state(cpp11::sexp ptr) {
   auto *obj = cpp11::as_cpp<cpp11::external_pointer<filter<T>>>(ptr).get();
-  const auto state_filter = rng_state_as_raw(obj->rng_state());
-  const auto state_model = rng_state_as_raw(obj->model.rng_state());
-  return cpp11::writable::list{state_filter, state_model};
+  using rng_state_type = typename T::rng_state_type;
+
+  // Undo the construction as above so that the rng state comes out in
+  // the same format it goes in, as a single raw vector.
+  const auto& state_filter = obj->rng_state();
+  const auto& state_model = obj->model.rng_state();
+  const auto n_particles = obj->model.n_particles();
+  const auto n_groups = obj->model.n_groups();
+  const auto n_state = rng_state_type::size();
+  const auto n_bytes = sizeof(typename rng_state_type::int_type);
+  const auto n_bytes_state = n_bytes * n_state;
+  cpp11::writable::raws ret(n_bytes * (state_filter.size() + state_model.size()));
+  for (size_t i = 0; i < n_groups; ++i) {
+    std::memcpy(RAW(ret) + i * n_bytes_state * (n_particles + 1),
+                state_filter.data() + i * n_state,
+                n_bytes_state);
+    std::memcpy(RAW(ret) + i * n_bytes_state * (n_particles + 1) + n_bytes_state,
+                state_model.data() + i * n_state * n_particles,
+                n_bytes_state * n_particles);
+  }
+
+  return ret;
 }
 
 }

tests/testthat/test-filter.R

@@ -136,7 +136,6 @@ test_that("can run particle filter", {
   obj <- dust2_cpu_sir_filter_alloc(
     pars, time_start, time, dt, data, n_particles, 0, seed)
   ptr <- obj[[1]]
-  s <- dust2_cpu_sir_filter_rng_state(ptr)
   res <- replicate(20, dust2_cpu_sir_filter_run(ptr, NULL, FALSE))
 
   cmp_filter <- sir_filter_manual(
@@ -166,10 +165,8 @@ test_that("can run a nested particle filter and get the same result", {
   ## Here, we can check the layout of the rng within the filter and model:
   n_streams <- (n_particles + 1) * 2
   r <- mcstate2::mcstate_rng$new(n_streams = n_streams, seed = seed)$state()
-  rr <- array(r, c(length(r) / n_streams, n_particles + 1, 2))
   s <- dust2_cpu_sir_filter_rng_state(ptr)
-  expect_equal(s[[1]], c(rr[, 1, ]))
-  expect_equal(s[[2]], c(rr[, -1, ]))
+  expect_equal(s, r)
 
   res <- replicate(20, dust2_cpu_sir_filter_run(ptr, NULL, TRUE))
 
@@ -181,12 +178,15 @@ test_that("can run a nested particle filter and get the same result", {
   s1 <- dust2_cpu_sir_filter_rng_state(ptr1)
   res1 <- replicate(20, dust2_cpu_sir_filter_run(ptr1, NULL, FALSE))
   expect_equal(res1, res[1, ])
+  expect_equal(s1, s[1:3232])
 
+  seed2 <- r[3233:3264]
   data2 <- lapply(data, "[[", 2)
   obj2 <- dust2_cpu_sir_filter_alloc(
-    pars[[2]], time_start, time, dt, data2, n_particles, 0, rr[, 1, 2])
+    pars[[2]], time_start, time, dt, data2, n_particles, 0, seed2)
   ptr2 <- obj2[[1]]
   s2 <- dust2_cpu_sir_filter_rng_state(ptr2)
   res2 <- replicate(20, dust2_cpu_sir_filter_run(ptr2, NULL, FALSE))
   expect_equal(res2, res[2, ])
+  expect_equal(s2, s[3233:6464])
 })