[libc-commits] [libc] ecd46d3 - [libc] Add `IN6_IS_ADDR_LOOPBACK` (#172312)

[via libc-commits]

Author: Connector Switch
Date: 2025-12-18T23:09:35+08:00
New Revision: ecd46d350aa63b28b5710fefbe69b88b51331a53

URL: https://github.com/llvm/llvm-project/commit/ecd46d350aa63b28b5710fefbe69b88b51331a53
DIFF: https://github.com/llvm/llvm-project/commit/ecd46d350aa63b28b5710fefbe69b88b51331a53.diff

LOG: [libc] Add `IN6_IS_ADDR_LOOPBACK` (#172312)

This patch adds the `IN6_IS_ADDR_LOOPBACK` macro, which checks whether
an address is loopback address.

Added: 
    

Modified: 
    libc/include/llvm-libc-macros/netinet-in-macros.h
    libc/test/include/netinet_in_test.cpp

Removed: 
    


################################################################################
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));