[libc] Add IN6_IS_ADDR_MC* (#172643)

This patch adds the `IN6_IS_ADDR_MC*` macro, which checks whether an
address is multicast node-local address, multicast link-local address,
multicast site-local address, multicast organization-local address and
multicast global address.

Author: c8ef

libc/include/llvm-libc-macros/netinet-in-macros.h

@@ -64,4 +64,24 @@
   ((__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_MC_NODELOCAL(a)                                            \
+  (IN6_IS_ADDR_MULTICAST(a) &&                                                 \
+   (__LLVM_LIBC_CAST(reinterpret_cast, uint8_t *, a)[1] & 0xf) == 0x1)
+
+#define IN6_IS_ADDR_MC_LINKLOCAL(a)                                            \
+  (IN6_IS_ADDR_MULTICAST(a) &&                                                 \
+   (__LLVM_LIBC_CAST(reinterpret_cast, uint8_t *, a)[1] & 0xf) == 0x2)
+
+#define IN6_IS_ADDR_MC_SITELOCAL(a)                                            \
+  (IN6_IS_ADDR_MULTICAST(a) &&                                                 \
+   (__LLVM_LIBC_CAST(reinterpret_cast, uint8_t *, a)[1] & 0xf) == 0x5)
+
+#define IN6_IS_ADDR_MC_ORGLOCAL(a)                                             \
+  (IN6_IS_ADDR_MULTICAST(a) &&                                                 \
+   (__LLVM_LIBC_CAST(reinterpret_cast, uint8_t *, a)[1] & 0xf) == 0x8)
+
+#define IN6_IS_ADDR_MC_GLOBAL(a)                                               \
+  (IN6_IS_ADDR_MULTICAST(a) &&                                                 \
+   (__LLVM_LIBC_CAST(reinterpret_cast, uint8_t *, a)[1] & 0xf) == 0xe)
+
 #endif // LLVM_LIBC_MACROS_NETINET_IN_MACROS_H

libc/test/include/netinet_in_test.cpp

@@ -42,4 +42,18 @@ TEST(LlvmLibcNetinetInTest, IN6Macro) {
   buff[0] = 0xff;
   buff[1] = 0x80;
   EXPECT_FALSE(IN6_IS_ADDR_SITELOCAL(buff));
+
+  buff[0] = 0xff;
+  buff[1] = 0x1;
+  EXPECT_TRUE(IN6_IS_ADDR_MC_NODELOCAL(buff));
+  buff[1] = 0x2;
+  EXPECT_TRUE(IN6_IS_ADDR_MC_LINKLOCAL(buff));
+  buff[1] = 0x5;
+  EXPECT_TRUE(IN6_IS_ADDR_MC_SITELOCAL(buff));
+  buff[1] = 0x8;
+  EXPECT_TRUE(IN6_IS_ADDR_MC_ORGLOCAL(buff));
+  buff[1] = 0xe;
+  EXPECT_TRUE(IN6_IS_ADDR_MC_GLOBAL(buff));
+  buff[1] = 0;
+  buff[0] = 0;
 }