1 files changed, 40 insertions, 0 deletions
diff --git a/client/cpp/unix_kernel_rand_impl.cc b/client/cpp/unix_kernel_rand_impl.cc
new file mode 100644
index 0000000..e2a848c
--- /dev/null
+++ b/client/cpp/unix_kernel_rand_impl.cc
@@ -0,0 +1,40 @@
+// 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.
+
+#include "unix_kernel_rand_impl.h"
+
+#include <stdint.h>  // uint64_t
+
+namespace rappor {
+
+const int kMaxBitWidth = 32;  // also in encoder.cc
+
+bool UnixKernelRand::GetMask(float prob, int num_bits, Bits* mask_out) const {
+  uint8_t rand_buf[kMaxBitWidth];
+  size_t num_elems = fread(&rand_buf, sizeof(uint8_t), num_bits, fp_);
+  if (num_elems != static_cast<size_t>(num_bits)) {  // fread error
+    return false;
+  }
+  uint8_t threshold_256 = static_cast<uint8_t>(prob * 256);
+
+  Bits mask = 0;
+  for (int i = 0; i < num_bits; ++i) {
+    uint8_t bit = (rand_buf[i] < threshold_256);
+    mask |= (bit << i);
+  }
+  *mask_out = mask;
+  return true;
+}
+
+}  // namespace rappor