[llvm-branch-commits] [libc] [libc] Add `IN6_IS_ADDR_V4MAPPED` (PR #172645)

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https://github.com/c8ef created https://github.com/llvm/llvm-project/pull/172645

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>From 0a03867534b22394304030c6f933781b8bb60ea8 Mon Sep 17 00:00:00 2001
From: c8ef <c8ef at outlook.com>
Date: Wed, 17 Dec 2025 20:47:11 +0800
Subject: [PATCH] [libc] Add `IN6_IS_ADDR_V4MAPPED`

---
 libc/include/llvm-libc-macros/netinet-in-macros.h | 8 ++++++++
 libc/test/include/netinet_in_test.cpp             | 7 +++++++
 2 files changed, 15 insertions(+)

diff --git a/libc/include/llvm-libc-macros/netinet-in-macros.h b/libc/include/llvm-libc-macros/netinet-in-macros.h
index 88ffe92756b16..1d7bef833f2b8 100644
--- a/libc/include/llvm-libc-macros/netinet-in-macros.h
+++ b/libc/include/llvm-libc-macros/netinet-in-macros.h
@@ -64,6 +64,14 @@
   ((__LLVM_LIBC_CAST(reinterpret_cast, uint8_t *, a)[0]) == 0xfe &&            \
    (__LLVM_LIBC_CAST(reinterpret_cast, uint8_t *, a)[1] & 0xc0) == 0xc0)
 
+#define IN6_IS_ADDR_V4MAPPED(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, uint8_t *, a)[8]) == 0 &&               \
+   (__LLVM_LIBC_CAST(reinterpret_cast, uint8_t *, a)[9]) == 0 &&               \
+   (__LLVM_LIBC_CAST(reinterpret_cast, uint8_t *, a)[10]) == 0xff &&           \
+   (__LLVM_LIBC_CAST(reinterpret_cast, uint8_t *, a)[11]) == 0xff)
+
 #define IN6_IS_ADDR_MC_NODELOCAL(a)                                            \
   (IN6_IS_ADDR_MULTICAST(a) &&                                                 \
    (__LLVM_LIBC_CAST(reinterpret_cast, uint8_t *, a)[1] & 0xf) == 0x1)
diff --git a/libc/test/include/netinet_in_test.cpp b/libc/test/include/netinet_in_test.cpp
index 72500c4d51438..2f57080ef8b77 100644
--- a/libc/test/include/netinet_in_test.cpp
+++ b/libc/test/include/netinet_in_test.cpp
@@ -56,4 +56,11 @@ TEST(LlvmLibcNetinetInTest, IN6Macro) {
   EXPECT_TRUE(IN6_IS_ADDR_MC_GLOBAL(buff));
   buff[1] = 0;
   buff[0] = 0;
+
+  EXPECT_FALSE(IN6_IS_ADDR_V4MAPPED(buff));
+  buff[10] = 0xff;
+  buff[11] = 0xff;
+  EXPECT_TRUE(IN6_IS_ADDR_V4MAPPED(buff));
+  buff[10] = 0;
+  buff[11] = 0;
 }