Import of the watch repository from Pebble

src/fw/util/rand/rand.c

@@ -0,0 +1,100 @@
+/*
+ * Copyright 2024 Google LLC
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+///////////////////////////////////////
+// Implements:
+//   int rand(void);
+//   int rand_r(unsigned int *seedp);
+//   void srand(unsigned int seed);
+///////////////////////////////////////
+// Exports to apps:
+//   rand, srand
+///////////////////////////////////////
+// Notes:
+//   RNG implementation is using TinyMT
+//   Apps and Workers have unique RNG seed variables, all kernel tasks share an RNG seed.
+//   All other libc's seem to just segfault if seedp is NULL to rand_r; we assert instead.
+
+#include <math.h>
+#include <stddef.h>
+#include <stdint.h>
+#include <stdio.h>
+
+#include "kernel/pebble_tasks.h"
+#include "system/passert.h"
+#include "vendor/tinymt32/tinymt32.h"
+
+extern uint32_t *app_state_get_rand_ptr(void);
+extern uint32_t *worker_state_get_rand_ptr(void);
+
+// Kernel random seed
+static tinymt32_t s_kernel_rand = {{0}};
+
+static tinymt32_t *prv_get_seed_ptr(void) {
+  switch (pebble_task_get_current()) {
+    case PebbleTask_App:
+      return (tinymt32_t*)app_state_get_rand_ptr();
+    case PebbleTask_Worker:
+      return (tinymt32_t*)worker_state_get_rand_ptr();
+    default:
+      return &s_kernel_rand;
+  }
+}
+
+static void prv_seed(tinymt32_t *state, uint32_t seed) {
+  // Generated from ID 2841590142
+  // characteristic=9a1431e60e5e03b118c9173c2f60761f
+  // type=32
+  // id=2841590142
+  // mat1=d728239b
+  // mat2=57e7ffaf
+  // tmat=ebb03f7f
+  // weight=59
+  // delta=0
+
+  state->mat1 = 0xd728239b;
+  state->mat2 = 0x57e7ffaf;
+  state->tmat = 0xebb03f7f;
+  tinymt32_init(state, seed);
+}
+
+static int prv_next(tinymt32_t *state) {
+  if (state->mat1 == 0) { // Not initialized yet
+    prv_seed(state, 0x9a1431e6); // Just any ol' number
+  }
+  return tinymt32_generate_uint32(state);
+}
+
+uint32_t rand32(void) {
+  return prv_next(prv_get_seed_ptr());
+}
+
+int rand(void) {
+  return rand32() & 0x7FFFFFFF;
+}
+
+int rand_r(unsigned int *seedp) { // Please don't use this
+  PBL_ASSERTN(seedp != NULL);
+
+  tinymt32_t state = {{0}};
+  prv_seed(&state, *seedp);
+  *seedp = prv_next(&state) & 0x7FFFFFFF;
+  return *seedp;
+}
+
+void srand(unsigned int seed) {
+  prv_seed(prv_get_seed_ptr(), seed);
+}