[libc] Add IN6_IS_ADDR_{LINK, SITE}LOCAL

[c8ef]

This patch introduces two macros in netinet/in.h. The redundant tests for macro values in the testcases have been removed.

[llvmbot]

@llvm/pr-subscribers-libc

Author: Connector Switch (c8ef)

Changes

---

Full diff: https://github.com/llvm/llvm-project/pull/168207.diff

2 Files Affected:

• (modified) libc/include/llvm-libc-macros/netinet-in-macros.h (+8)
• (modified) libc/test/include/netinet_in_test.cpp (+15-16)

diff --git a/libc/include/llvm-libc-macros/netinet-in-macros.h b/libc/include/llvm-libc-macros/netinet-in-macros.h
index 2011c34e288cd..c0d8c19045154 100644
--- a/libc/include/llvm-libc-macros/netinet-in-macros.h
+++ b/libc/include/llvm-libc-macros/netinet-in-macros.h
@@ -33,4 +33,12 @@
 #define INET_ADDRSTRLEN 16
 #define INET6_ADDRSTRLEN 46
 
+#define IN6_IS_ADDR_LINKLOCAL(a)                                               \
+  ((__LLVM_LIBC_CAST(reinterpret_cast, uint8_t *, a)[0]) == 0xfe &&            \
+   (__LLVM_LIBC_CAST(reinterpret_cast, uint8_t *, a)[1] & 0xc0) == 0x80)
+
+#define IN6_IS_ADDR_SITELOCAL(a)                                               \
+  ((__LLVM_LIBC_CAST(reinterpret_cast, uint8_t *, a)[0]) == 0xfe &&            \
+   (__LLVM_LIBC_CAST(reinterpret_cast, uint8_t *, a)[1] & 0xc0) == 0xc0)
+
 #endif // LLVM_LIBC_MACROS_NETINET_IN_MACROS_H
diff --git a/libc/test/include/netinet_in_test.cpp b/libc/test/include/netinet_in_test.cpp
index 714892f511b1c..6937262f92e90 100644
--- a/libc/test/include/netinet_in_test.cpp
+++ b/libc/test/include/netinet_in_test.cpp
@@ -9,21 +9,20 @@
 #include "include/llvm-libc-macros/netinet-in-macros.h"
 #include "test/UnitTest/Test.h"
 
-TEST(LlvmLibcNetinetInTest, IPPROTOMacro) {
-  EXPECT_EQ(IPPROTO_IP, 0);
-  EXPECT_EQ(IPPROTO_ICMP, 1);
-  EXPECT_EQ(IPPROTO_TCP, 6);
-  EXPECT_EQ(IPPROTO_UDP, 17);
-  EXPECT_EQ(IPPROTO_IPV6, 41);
-  EXPECT_EQ(IPPROTO_RAW, 255);
-}
+TEST(LlvmLibcNetinetInTest, IN6Macro) {
+  char buff[16] = {};
+
+  buff[0] = 0xfe;
+  buff[1] = 0x80;
+  EXPECT_TRUE(IN6_IS_ADDR_LINKLOCAL(buff));
+  buff[0] = 0xff;
+  buff[1] = 0x80;
+  EXPECT_FALSE(IN6_IS_ADDR_LINKLOCAL(buff));
 
-TEST(LlvmLibcNetinetInTest, IPV6Macro) {
-  EXPECT_EQ(IPV6_UNICAST_HOPS, 16);
-  EXPECT_EQ(IPV6_MULTICAST_IF, 17);
-  EXPECT_EQ(IPV6_MULTICAST_HOPS, 18);
-  EXPECT_EQ(IPV6_MULTICAST_LOOP, 19);
-  EXPECT_EQ(IPV6_JOIN_GROUP, 20);
-  EXPECT_EQ(IPV6_LEAVE_GROUP, 21);
-  EXPECT_EQ(IPV6_V6ONLY, 26);
+  buff[0] = 0xfe;
+  buff[1] = 0xc0;
+  EXPECT_TRUE(IN6_IS_ADDR_SITELOCAL(buff));
+  buff[0] = 0xff;
+  buff[1] = 0x80;
+  EXPECT_FALSE(IN6_IS_ADDR_SITELOCAL(buff));
 }

[lntue]

I guess we are not worrying about endianness for now?

[c8ef]

I'm not sure I follow here. Does this mean we can assume all our supported host platforms are little-endian now? I think the current implementation can support both endianness.

[lntue]

This is testing byte 0 == 0xfe and byte 1 & mask == 80, so assuming the high parts of 32-bit address a are at byte 0 and 1, that's big endian. Are we assuming a will be big endian, or does it depend on the host?

[c8ef]

Are we assuming a will be big endian

Yes.

Quote from manpages: Each macro is of type int and takes a single argument of type const struct in6_addr *

struct in6_addr is required by the standard to store the address in Network Byte Order (Big Endian). This means the most significant byte is always at memory offset 0, regardless of the host architecture.

[lntue]

Do you mind adding the explanation + reference to a comment here, so that this question won't come up in the future? Thanks,

[c8ef]

Done.

[michaelrj-google]

Overall looks good to me, please edit the PR description so it doesn't @ me before merging. If merged as-is it will ping me every time someone pushes a copy of this commit to github which is a little annoying.

[c8ef]

Overall looks good to me, please edit the PR description so it doesn't @ me before merging. If merged as-is it will ping me every time someone pushes a copy of this commit to github which is a little annoying.

Done.