1 files changed, 44 insertions, 0 deletions
diff --git a/client/cpp/libc_rand_impl.cc b/client/cpp/libc_rand_impl.cc
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+// Copyright 2015 Google Inc. All rights reserved.
+//
+// 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.
+
+// IMPORTANT: This is for demo /simulation purposes only.  Use a better random
+// function in production applications.
+
+#include "libc_rand_impl.h"
+
+#include <assert.h>
+#include <stdint.h>  // uint64_t
+#include <stdlib.h>  // srand
+
+namespace rappor {
+
+//
+// LibcRand
+//
+
+// Similar to client/python/fastrand.c
+bool LibcRand::GetMask(float prob, int num_bits, Bits* mask_out) const {
+  int rand_threshold = static_cast<int>(prob * RAND_MAX);
+  Bits mask = 0;
+
+  for (int i = 0; i < num_bits; ++i) {
+    // NOTE: could use rand_r(), which is more thread-safe
+    Bits bit = (rand() < rand_threshold);
+    mask |= (bit << i);
+  }
+  *mask_out = mask;
+  return true;  // no possible failure
+}
+
+}  // namespace rappor