[libc-commits] [libc] [libc] Add `IN6_IS_ADDR_LOOPBACK` (PR #172312)

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https://github.com/c8ef updated https://github.com/llvm/llvm-project/pull/172312

>From db2ebdaffba2c2ba9d76a92ed06b7c6c946f05a2 Mon Sep 17 00:00:00 2001
From: c8ef <c8ef at outlook.com>
Date: Mon, 15 Dec 2025 22:47:59 +0800
Subject: [PATCH 1/2] [libc] Add `IN6_IS_ADDR_UNSPECIFIED`

---
 libc/include/llvm-libc-macros/netinet-in-macros.h | 6 ++++++
 libc/test/include/netinet_in_test.cpp             | 7 +++++++
 2 files changed, 13 insertions(+)

diff --git a/libc/include/llvm-libc-macros/netinet-in-macros.h b/libc/include/llvm-libc-macros/netinet-in-macros.h
index b04d6aa4b6781..f97a2dd0c3fda 100644
--- a/libc/include/llvm-libc-macros/netinet-in-macros.h
+++ b/libc/include/llvm-libc-macros/netinet-in-macros.h
@@ -38,6 +38,12 @@
 // 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_UNSPECIFIED(a)                                             \
+  ((__LLVM_LIBC_CAST(reinterpret_cast, uint32_t *, a)[0]) == 0 &&              \
+   (__LLVM_LIBC_CAST(reinterpret_cast, uint32_t *, a)[1]) == 0 &&              \
+   (__LLVM_LIBC_CAST(reinterpret_cast, uint32_t *, a)[2]) == 0 &&              \
+   (__LLVM_LIBC_CAST(reinterpret_cast, uint32_t *, a)[3]) == 0)
+
 #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)
diff --git a/libc/test/include/netinet_in_test.cpp b/libc/test/include/netinet_in_test.cpp
index 6937262f92e90..d70c780800858 100644
--- a/libc/test/include/netinet_in_test.cpp
+++ b/libc/test/include/netinet_in_test.cpp
@@ -12,6 +12,13 @@
 TEST(LlvmLibcNetinetInTest, IN6Macro) {
   char buff[16] = {};
 
+  EXPECT_TRUE(IN6_IS_ADDR_UNSPECIFIED(buff));
+  for (int i = 0; i < 16; ++i) {
+    buff[i] = 1;
+    EXPECT_FALSE(IN6_IS_ADDR_UNSPECIFIED(buff));
+    buff[i] = 0;
+  }
+
   buff[0] = 0xfe;
   buff[1] = 0x80;
   EXPECT_TRUE(IN6_IS_ADDR_LINKLOCAL(buff));

>From 77c407bc401353723cc0a5d684c9e17102d0559b Mon Sep 17 00:00:00 2001
From: c8ef <c8ef at outlook.com>
Date: Mon, 15 Dec 2025 23:01:04 +0800
Subject: [PATCH 2/2] [libc] Add `IN6_IS_ADDR_LOOPBACK`

---
 libc/include/llvm-libc-macros/netinet-in-macros.h | 9 +++++++++
 libc/test/include/netinet_in_test.cpp             | 5 +++++
 2 files changed, 14 insertions(+)

diff --git a/libc/include/llvm-libc-macros/netinet-in-macros.h b/libc/include/llvm-libc-macros/netinet-in-macros.h
index f97a2dd0c3fda..3148aed6bb112 100644
--- a/libc/include/llvm-libc-macros/netinet-in-macros.h
+++ b/libc/include/llvm-libc-macros/netinet-in-macros.h
@@ -44,6 +44,15 @@
    (__LLVM_LIBC_CAST(reinterpret_cast, uint32_t *, a)[2]) == 0 &&              \
    (__LLVM_LIBC_CAST(reinterpret_cast, uint32_t *, a)[3]) == 0)
 
+#define IN6_IS_ADDR_LOOPBACK(a)                                                \
+  ((__LLVM_LIBC_CAST(reinterpret_cast, uint32_t *, a)[0]) == 0 &&              \
+   (__LLVM_LIBC_CAST(reinterpret_cast, uint32_t *, a)[1]) == 0 &&              \
+   (__LLVM_LIBC_CAST(reinterpret_cast, uint32_t *, a)[2]) == 0 &&              \
+   (__LLVM_LIBC_CAST(reinterpret_cast, uint8_t *, a)[12]) == 0 &&              \
+   (__LLVM_LIBC_CAST(reinterpret_cast, uint8_t *, a)[13]) == 0 &&              \
+   (__LLVM_LIBC_CAST(reinterpret_cast, uint8_t *, a)[14]) == 0 &&              \
+   (__LLVM_LIBC_CAST(reinterpret_cast, uint8_t *, a)[15]) == 1)
+
 #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)
diff --git a/libc/test/include/netinet_in_test.cpp b/libc/test/include/netinet_in_test.cpp
index d70c780800858..15e57ccef7ac5 100644
--- a/libc/test/include/netinet_in_test.cpp
+++ b/libc/test/include/netinet_in_test.cpp
@@ -19,6 +19,11 @@ TEST(LlvmLibcNetinetInTest, IN6Macro) {
     buff[i] = 0;
   }
 
+  EXPECT_FALSE(IN6_IS_ADDR_LOOPBACK(buff));
+  buff[15] = 1;
+  EXPECT_TRUE(IN6_IS_ADDR_LOOPBACK(buff));
+  buff[15] = 0;
+
   buff[0] = 0xfe;
   buff[1] = 0x80;
   EXPECT_TRUE(IN6_IS_ADDR_LINKLOCAL(buff));