[libc] Implement ntohl and ntohs

[rtenneti]

Summary

Per spec:

https://pubs.opengroup.org/onlinepubs/9699919799/functions/ntohl.html
https://pubs.opengroup.org/onlinepubs/9699919799/functions/ntohs.html

Co-authored-by: Jeff Bailey <[e-mail]>

[sivachandra]

libc/src/network/ntohl.cpp

16

Should this always convert to big-endian, or should it convert to the host's endianness?

[rtenneti]

libc/src/network/ntohl.cpp

16

I thought of implementing it as the following:

LLVM_LIBC_FUNCTION(uint32_t, ntohl, (uint32_t netlong)) {

return Endian::IS_LITTLE ? __builtin_bswap32(netlong) : netlong;

}

The above seem to be same as Endian::to_big_endian. I am wondering if it is better to implement the above (to be clearer). What do you think? Thanks

[rtenneti]

+ Added explicit check for IS_LITTLE to do the swap.
+ Added a test to verify htonl(ntohl(orig)) == orig.

[rtenneti]

Hi Siva,

Added a htonl(ntohl(...)) test. Did the swap based on host's endianess. PTAL.

[sivachandra]

libc/src/network/ntohl.cpp

16

I think this is cleaner. One more suggestion - use a constexpr if statement like this:

if constexpr (Endian::IS_LITTLE)
  return __builtin_bswap(netlong);
else
  return netlong;

[rtenneti]

Fixed comments.

[rtenneti]

Did a git pull rebase false to merge the latest changes.

[sivachandra]

Not sure what happened here, but the diff is not related to the topic of this change.

[rtenneti]

Ran git restore on llvm files.

[rtenneti]

Dif a git pull --rebase.

[rtenneti]

Fixed comments.

[rtenneti]

Fixing Siva's comments.

libc/src/network/ntohl.cpp

 //===-- Implementation of ntohl function ----------------------------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
 #include "src/network/ntohl.h"
 #include "src/__support/common.h"
 #include "src/__support/endian.h"
 
 namespace __llvm_libc {
 
 LLVM_LIBC_FUNCTION(uint32_t, ntohl, (uint32_t netlong)) {
-  return Endian::IS_LITTLE ? __builtin_bswap32(netlong) : netlong;
+  if constexpr (Endian::IS_LITTLE)
+    return __builtin_bswap32(netlong);
+  else
+    return netlong;
 }
 
 } // namespace __llvm_libc

libc/src/network/ntohs.cpp

 //===-- Implementation of ntohs function ----------------------------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
 #include "src/network/ntohs.h"
 #include "src/__support/common.h"
 #include "src/__support/endian.h"
 
 namespace __llvm_libc {
 
 LLVM_LIBC_FUNCTION(uint16_t, ntohs, (uint16_t netshort)) {
-  return Endian::IS_LITTLE ? __builtin_bswap16(netshort) : netshort;
+  if constexpr (Endian::IS_LITTLE)
+    return __builtin_bswap16(netshort);
+  else
+    return netshort;
 }
 
 } // namespace __llvm_libc