Adds audio_utils/safe_math.h for safe add / sub

[android-x86/system-media.git] / audio_utils / include / audio_utils / safe_math.h

diff --git a/audio_utils/include/audio_utils/safe_math.h b/audio_utils/include/audio_utils/safe_math.h
new file mode 100644 (file)
index 0000000..7dcab3f
--- /dev/null
+++ b/audio_utils/include/audio_utils/safe_math.h
@@ -0,0 +1,49 @@
+/*
+ * Copyright (C) 2019 The Android Open Source Project
+ *
+ * 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.
+ */
+
+namespace android::audio_utils {
+
+// safe_sub_overflow is used ensure that subtraction occurs in the same native
+// type with proper 2's complement overflow.  Without calling this function, it
+// is possible, for example, that optimizing compilers may elect to treat 32 bit
+// subtraction as 64 bit subtraction when storing into a 64 bit destination as
+// integer overflow is technically undefined.
+template <typename T, typename U,
+          typename = std::enable_if_t<
+              std::is_same<std::decay_t<T>, std::decay_t<U>>{}>>
+// ensure arguments are same type (ignoring volatile, which is used in cblk
+// variables).
+auto safe_sub_overflow(const T& a, const U& b) {
+  std::decay_t<T> result;
+  (void)__builtin_sub_overflow(a, b, &result);
+  // note if __builtin_sub_overflow returns true, an overflow occurred.
+  return result;
+}
+
+// similar to safe_sub_overflow but for add operator.
+template <typename T, typename U,
+          typename = std::enable_if_t<
+              std::is_same<std::decay_t<T>, std::decay_t<U>>{}>>
+// ensure arguments are same type (ignoring volatile, which is used in cblk
+// variables).
+auto safe_add_overflow(const T& a, const U& b) {
+  std::decay_t<T> result;
+  (void)__builtin_add_overflow(a, b, &result);
+  // note if __builtin_add_overflow returns true, an overflow occurred.
+  return result;
+}
+
+} // namespace android::audio_utils