[libc-commits] [libc] [libc] Add `IN6_IS_ADDR_{LINK, SITE}LOCAL` (PR #168207)

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https://github.com/c8ef updated https://github.com/llvm/llvm-project/pull/168207

>From 557b4bf26ed7f5193d2d9f78809d5254ef4d8587 Mon Sep 17 00:00:00 2001
From: c8ef <c8ef at outlook.com>
Date: Sat, 15 Nov 2025 22:52:02 +0800
Subject: [PATCH 1/2] [libc] Add IN6_IS_ADDR_{LINK, SITE}LOCAL

---
 .../llvm-libc-macros/netinet-in-macros.h      |  8 +++++
 libc/test/include/netinet_in_test.cpp         | 31 +++++++++----------
 2 files changed, 23 insertions(+), 16 deletions(-)

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));
 }

>From f1a3ad72c92ecb0527eaf8b70be81fd0602b5946 Mon Sep 17 00:00:00 2001
From: c8ef <c8ef at outlook.com>
Date: Thu, 11 Dec 2025 01:08:35 +0800
Subject: [PATCH 2/2] add comments

---
 libc/include/llvm-libc-macros/netinet-in-macros.h | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/libc/include/llvm-libc-macros/netinet-in-macros.h b/libc/include/llvm-libc-macros/netinet-in-macros.h
index c0d8c19045154..599d31edca019 100644
--- a/libc/include/llvm-libc-macros/netinet-in-macros.h
+++ b/libc/include/llvm-libc-macros/netinet-in-macros.h
@@ -33,6 +33,10 @@
 #define INET_ADDRSTRLEN 16
 #define INET6_ADDRSTRLEN 46
 
+// The following macros test for special IPv6 addresses. Each macro is of type
+// int and takes a single argument of type const struct in6_addr *:
+// https://pubs.opengroup.org/onlinepubs/9799919799/basedefs/netinet_in.h.html
+
 #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)