Add cross-platform <android-base/endian.h>.

Bionic has <sys/endian.h>, glibc <endian.h>, and macOS and Windows have
nothing. This has often been annoying.

Bug: N/A
Test: new tests
Change-Id: I2a40c570df6a9bb30607ace1af653265938cc4b8

base/Android.bp

@@ -78,6 +78,7 @@ cc_test {
     host_supported: true,
     clang: true,
     srcs: [
+        "endian_test.cpp",
         "errors_test.cpp",
         "file_test.cpp",
         "logging_test.cpp",

base/endian_test.cpp

@@ -0,0 +1,69 @@
+/*
+ * Copyright (C) 2017 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.
+ */
+
+#include "android-base/endian.h"
+
+#include <gtest/gtest.h>
+
+TEST(endian, constants) {
+  ASSERT_TRUE(__LITTLE_ENDIAN == LITTLE_ENDIAN);
+  ASSERT_TRUE(__BIG_ENDIAN == BIG_ENDIAN);
+  ASSERT_TRUE(__BYTE_ORDER == BYTE_ORDER);
+
+  ASSERT_EQ(__LITTLE_ENDIAN, __BYTE_ORDER);
+}
+
+TEST(endian, smoke) {
+  static constexpr uint16_t le16 = 0x1234;
+  static constexpr uint32_t le32 = 0x12345678;
+  static constexpr uint64_t le64 = 0x123456789abcdef0;
+
+  static constexpr uint16_t be16 = 0x3412;
+  static constexpr uint32_t be32 = 0x78563412;
+  static constexpr uint64_t be64 = 0xf0debc9a78563412;
+
+  ASSERT_EQ(be16, htons(le16));
+  ASSERT_EQ(be32, htonl(le32));
+  ASSERT_EQ(be64, htonq(le64));
+
+  ASSERT_EQ(le16, ntohs(be16));
+  ASSERT_EQ(le32, ntohl(be32));
+  ASSERT_EQ(le64, ntohq(be64));
+
+  ASSERT_EQ(be16, htobe16(le16));
+  ASSERT_EQ(be32, htobe32(le32));
+  ASSERT_EQ(be64, htobe64(le64));
+
+  ASSERT_EQ(le16, betoh16(be16));
+  ASSERT_EQ(le32, betoh32(be32));
+  ASSERT_EQ(le64, betoh64(be64));
+
+  ASSERT_EQ(le16, htole16(le16));
+  ASSERT_EQ(le32, htole32(le32));
+  ASSERT_EQ(le64, htole64(le64));
+
+  ASSERT_EQ(le16, letoh16(le16));
+  ASSERT_EQ(le32, letoh32(le32));
+  ASSERT_EQ(le64, letoh64(le64));
+
+  ASSERT_EQ(le16, be16toh(be16));
+  ASSERT_EQ(le32, be32toh(be32));
+  ASSERT_EQ(le64, be64toh(be64));
+
+  ASSERT_EQ(le16, le16toh(le16));
+  ASSERT_EQ(le32, le32toh(le32));
+  ASSERT_EQ(le64, le64toh(le64));
+}

base/include/android-base/endian.h

@@ -0,0 +1,90 @@
+/*
+ * Copyright (C) 2017 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.
+ */
+
+#ifndef ANDROID_BASE_ENDIAN_H
+#define ANDROID_BASE_ENDIAN_H
+
+/* A cross-platform equivalent of bionic's <sys/endian.h>. */
+
+#if defined(__BIONIC__)
+
+#include <sys/endian.h>
+
+#elif defined(__GLIBC__)
+
+/* glibc's <endian.h> is like bionic's <sys/endian.h>. */
+#include <endian.h>
+
+/* glibc keeps htons and htonl in <netinet/in.h>. */
+#include <netinet/in.h>
+
+/* glibc doesn't have the 64-bit variants. */
+#define htonq(x) htobe64(x)
+#define ntohq(x) be64toh(x)
+
+/* glibc has different names to BSD for these. */
+#define betoh16(x) be16toh(x)
+#define betoh32(x) be32toh(x)
+#define betoh64(x) be64toh(x)
+
+#else
+
+/* Mac OS and Windows have nothing. */
+
+#define __LITTLE_ENDIAN 1234
+#define LITTLE_ENDIAN __LITTLE_ENDIAN
+
+#define __BIG_ENDIAN 4321
+#define BIG_ENDIAN __BIG_ENDIAN
+
+#define __BYTE_ORDER __LITTLE_ENDIAN
+#define BYTE_ORDER __BYTE_ORDER
+
+#define htons(x) __builtin_bswap16(x)
+#define htonl(x) __builtin_bswap32(x)
+#define htonq(x) __builtin_bswap64(x)
+
+#define ntohs(x) __builtin_bswap16(x)
+#define ntohl(x) __builtin_bswap32(x)
+#define ntohq(x) __builtin_bswap64(x)
+
+#define htobe16(x) __builtin_bswap16(x)
+#define htobe32(x) __builtin_bswap32(x)
+#define htobe64(x) __builtin_bswap64(x)
+
+#define betoh16(x) __builtin_bswap16(x)
+#define betoh32(x) __builtin_bswap32(x)
+#define betoh64(x) __builtin_bswap64(x)
+
+#define htole16(x) (x)
+#define htole32(x) (x)
+#define htole64(x) (x)
+
+#define letoh16(x) (x)
+#define letoh32(x) (x)
+#define letoh64(x) (x)
+
+#define be16toh(x) __builtin_bswap16(x)
+#define be32toh(x) __builtin_bswap32(x)
+#define be64toh(x) __builtin_bswap64(x)
+
+#define le16toh(x) (x)
+#define le32toh(x) (x)
+#define le64toh(x) (x)
+
+#endif
+
+#endif  // ANDROID_BASE_ENDIAN_H