Add a constexpr std::initializer_list<> constructor to HasBits

This provides easy constant / default initialization of donated string bit masks

PiperOrigin-RevId: 547362713

src/google/protobuf/BUILD.bazel

@@ -533,6 +533,17 @@ cc_library(
     ],
 )
 
+cc_test(
+    name = "has_bits_test",
+    srcs = ["has_bits_test.cc"],
+    copts = COPTS,
+    deps = [
+        ":protobuf_lite",
+        "@com_google_googletest//:gtest",
+        "@com_google_googletest//:gtest_main",
+    ],
+)
+
 cc_library(
     name = "protobuf",
     copts = COPTS,

src/google/protobuf/has_bits.h

@@ -31,6 +31,8 @@
 #ifndef GOOGLE_PROTOBUF_HAS_BITS_H__
 #define GOOGLE_PROTOBUF_HAS_BITS_H__
 
+#include <initializer_list>
+
 #include "google/protobuf/stubs/common.h"
 #include "google/protobuf/port.h"
 
@@ -50,6 +52,10 @@ class HasBits {
  public:
   PROTOBUF_NDEBUG_INLINE constexpr HasBits() : has_bits_{} {}
 
+  constexpr HasBits(std::initializer_list<uint32_t> has_bits) : has_bits_{} {
+    Copy(has_bits_, &*has_bits.begin(), has_bits.size());
+  }
+
   PROTOBUF_NDEBUG_INLINE void Clear() {
     memset(has_bits_, 0, sizeof(has_bits_));
   }
@@ -77,6 +83,21 @@ class HasBits {
   bool empty() const;
 
  private:
+  // Unfortunately, older GCC compilers (and perhaps others) fail on initializer
+  // arguments for an std::array<> or any type of array constructor. Below is a
+  // handrolled constexpr 'Copy' function that we use to make a constexpr
+  // constructor that accepts a `std::initializer` list.
+  static inline constexpr void Copy(uint32_t* dst, const uint32_t* src,
+                                    size_t n) {
+    assert(n <= doublewords);
+    for (size_t ix = 0; ix < n; ++ix) {
+      dst[ix] = src[ix];
+    }
+    for (size_t ix = n; ix < doublewords; ++ix) {
+      dst[ix] = 0;
+    }
+  }
+
   uint32_t has_bits_[doublewords];
 };
 
@@ -102,8 +123,8 @@ inline bool HasBits<4>::empty() const {
 
 template <int doublewords>
 inline bool HasBits<doublewords>::empty() const {
-  for (int i = 0; i < doublewords; ++i) {
-    if (has_bits_[i]) return false;
+  for (uint32_t bits : has_bits_) {
+    if (bits) return false;
   }
   return true;
 }

src/google/protobuf/has_bits_test.cc

@@ -0,0 +1,131 @@
+// Protocol Buffers - Google's data interchange format
+// Copyright 2023 Google Inc.  All rights reserved.
+// https://developers.google.com/protocol-buffers/
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+//     * Neither the name of Google Inc. nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+#include "google/protobuf/has_bits.h"
+
+#include <gmock/gmock.h>
+#include <gtest/gtest.h>
+
+namespace google {
+namespace protobuf {
+namespace internal {
+namespace {
+
+using ::testing::Eq;
+
+template <int n>
+void TestDefaultInit() {
+  HasBits<n> bits;
+  EXPECT_TRUE(bits.empty());
+  for (int i = 0; i < n; ++i) {
+    EXPECT_THAT(bits[i], Eq(0));
+  }
+}
+
+TEST(HasBits, DefaultInit) {
+  TestDefaultInit<1>();
+  TestDefaultInit<2>();
+  TestDefaultInit<3>();
+  TestDefaultInit<4>();
+}
+
+TEST(HasBits, ValueInit) {
+  {
+    HasBits<4> bits;
+    EXPECT_TRUE(bits.empty());
+  }
+  {
+    HasBits<4> bits({});
+    EXPECT_TRUE(bits.empty());
+  }
+  {
+    HasBits<4> bits({1});
+    EXPECT_FALSE(bits.empty());
+    EXPECT_THAT(bits[0], Eq(1));
+  }
+  {
+    HasBits<4> bits({1, 2, 3, 4});
+    EXPECT_FALSE(bits.empty());
+    EXPECT_THAT(bits[0], Eq(1));
+    EXPECT_THAT(bits[1], Eq(2));
+    EXPECT_THAT(bits[2], Eq(3));
+    EXPECT_THAT(bits[3], Eq(4));
+  }
+}
+
+TEST(HasBits, ConstexprValueInit) {
+  {
+    constexpr HasBits<4> bits;
+    EXPECT_TRUE(bits.empty());
+  }
+  {
+    constexpr HasBits<4> bits({});
+    EXPECT_TRUE(bits.empty());
+  }
+  {
+    constexpr HasBits<4> bits({1});
+    EXPECT_FALSE(bits.empty());
+    EXPECT_THAT(bits[0], Eq(1));
+  }
+  {
+    constexpr HasBits<4> bits({1, 2, 3, 4});
+    EXPECT_FALSE(bits.empty());
+    EXPECT_THAT(bits[0], Eq(1));
+    EXPECT_THAT(bits[1], Eq(2));
+    EXPECT_THAT(bits[2], Eq(3));
+    EXPECT_THAT(bits[3], Eq(4));
+  }
+}
+
+TEST(HasBits, operator_equal) {
+  EXPECT_FALSE(HasBits<4>({1, 2, 3, 4}) == HasBits<4>({0, 2, 3, 4}));
+  EXPECT_FALSE(HasBits<4>({1, 2, 3, 4}) == HasBits<4>({1, 0, 3, 4}));
+  EXPECT_FALSE(HasBits<4>({1, 2, 3, 4}) == HasBits<4>({1, 2, 0, 4}));
+  EXPECT_FALSE(HasBits<4>({1, 2, 3, 4}) == HasBits<4>({1, 2, 3, 0}));
+  EXPECT_TRUE(HasBits<4>({1, 2, 3, 4}) == HasBits<4>({1, 2, 3, 4}));
+}
+
+TEST(HasBits, Or) {
+  HasBits<4> bits1({1, 2, 4, 8});
+  HasBits<4> bits2({16, 32, 64, 128});
+  bits1.Or(bits2);
+  EXPECT_TRUE(bits1 == HasBits<4>({17, 34, 68, 136}));
+}
+
+TEST(HasBits, Copy) {
+  HasBits<4> bits1({1, 2, 4, 8});
+  HasBits<4> bits2(bits1);
+  EXPECT_TRUE(bits1 == bits2);
+}
+
+}  // namespace
+}  // namespace internal
+}  // namespace protobuf
+}  // namespace google