[libc] Add strlen implementation.

[PaulkaToast]

Summary

Along with the parent patch, this should fix the last call to a non internal libc function.

[xbolva00]

libc/src/string/strcat.cpp

17–18

Remove outdated comment

[PaulkaToast]

libc/src/string/strcat.cpp

17–18

Good catch, thanks!

[abrachet]

libc/src/string/strcpy.cpp

16

We could make these __restrict while we're here but I think it there might be no benefit given we just call memcpy.

libc/src/string/strlen.cpp

17

Brackets not common for single statement loops.

libc/src/string/strlen.h

1

We could add the -*- C++ -*-

libc/test/src/string/strlen_test.cpp

17

Maybe 0UL and 12UL whichever you think looks better.

[PaulkaToast]

libc/src/string/strlen.h

1

Just noticed none of the headers in string have this. I'll go make a separate patch for that. Thanks!

libc/test/src/string/strlen_test.cpp

17

Ah, good point! I think I prefer the explicit cast because its very obvious what type it is.

[sivachandra]

Couple of nits inline but LGTM.

libc/src/string/strlen.cpp

15–21

Can you add a TODO here saying that one could improve this by making use of the alignment and target machine word size information?

libc/src/string/strlen.h

1

This problem is probably more wide spread than just the string directory. +1 to fixing them all up in a separate, may be obvious patch.

13

Do you still need to include stddef.h if you include include/string.h? In my patches, I have included the public header iff required. For example, the public header defines a header which is required by the API declared here. So, keeping stddef.h and removing include/string.h is also fine. Whatever you choose, share your thoughts so that I can learn if I am missing something.

[sivachandra]

libc/src/string/strlen.h

13

I mean't to say, "For example, if the public header defines a *struct* which is required by the API declared here."

[MaskRay]

libc/src/string/strlen.cpp

18

https://llvm.org/docs/CodingStandards.html#prefer-preincrement

libc/src/string/strlen.h

1

https://llvm.org/docs/CodingStandards.html#file-headers

[PaulkaToast]

libc/src/string/strlen.cpp

15–21

Added a more general comment about looking into the performance of this function.

libc/src/string/strlen.h

13

Thanks for bringing this up! I based this off the memcpy header without much consideration.

Now that I think about it more, it seems that both strlen and memcpy indirectly include stddef.h from include/string.h. I think it makes more sense to use the include/string.h approach as that will be more consistent and would require less code duplication in terms of figuring out which entrypoints depend on which headers.

[PaulkaToast]

libc/src/string/strlen.h

1

Agreed I can send something out for this shortly.

[PaulkaToast]

libc/src/string/strlen.cpp

18

This is great suggestion thank you! (:

libc/fuzzing/string/CMakeLists.txt

 add_libc_fuzzer(
   strcpy_fuzz
   SRCS
     strcpy_fuzz.cpp
   DEPENDS
     strcpy
+    strlen
 )

libc/src/string/CMakeLists.txt

 add_subdirectory(memory_utils)
 
 add_entrypoint_object(
   strcat
   SRCS
     strcat.cpp
   HDRS
     strcat.h
   DEPENDS
     strcpy
     string_h
+    strlen
 )
 
 add_entrypoint_object(
   strcpy
   SRCS
     strcpy.cpp
   HDRS
     strcpy.h
   DEPENDS
     string_h
+    strlen
+)
+
+add_entrypoint_object(
+  strlen
+  SRCS
+    strlen.cpp
+  HDRS
+    strlen.h
+  DEPENDS
+    string_h
 )
 
 # ------------------------------------------------------------------------------
 # memcpy
 # ------------------------------------------------------------------------------
 
 # include the relevant architecture specific implementations
 if(${LIBC_TARGET_MACHINE} STREQUAL "x86_64")

libc/src/string/strcat.cpp

 //===-------------------- Implementation of strcat -----------------------===//
 //
 // 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/string/strcat.h"
+#include "src/string/strcpy.h"
+#include "src/string/strlen.h"
 
 #include "src/__support/common.h"
-#include "src/string/strcpy.h"
 
 namespace __llvm_libc {
 
 char *LLVM_LIBC_ENTRYPOINT(strcat)(char *dest, const char *src) {
-  // We do not yet have an implementaion of strlen in so we will use strlen
-  // from another libc.
-  __llvm_libc::strcpy(dest + ::strlen(dest), src);
+  __llvm_libc::strcpy(dest + __llvm_libc::strlen(dest), src);
   return dest;
 }
 
 } // namespace __llvm_libc

libc/src/string/strcpy.cpp

 //===-------------------- Implementation of strcpy -----------------------===//
 //
 // 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/string/strcpy.h"
+#include "src/string/strlen.h"
 
 #include "src/__support/common.h"
 
 namespace __llvm_libc {
 
 char *LLVM_LIBC_ENTRYPOINT(strcpy)(char *dest, const char *src) {
-  return reinterpret_cast<char *>(::memcpy(dest, src, ::strlen(src) + 1));
+  return reinterpret_cast<char *>(
+      ::memcpy(dest, src, __llvm_libc::strlen(src) + 1));
 }
 
 } // namespace __llvm_libc

libc/src/string/strlen.h

-//===-------------------- Implementation of strcpy -----------------------===//
+//===----------------- Implementation header for strlen -------------------===//
 //
 // 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/string/strcpy.h"
+#ifndef LLVM_LIBC_SRC_STRING_STRLEN_H
+#define LLVM_LIBC_SRC_STRING_STRLEN_H
 
-#include "src/__support/common.h"
+#include "include/string.h"
 
 namespace __llvm_libc {
 
-char *LLVM_LIBC_ENTRYPOINT(strcpy)(char *dest, const char *src) {
-  return reinterpret_cast<char *>(::memcpy(dest, src, ::strlen(src) + 1));
-}
+size_t strlen(const char *src);
 
 } // namespace __llvm_libc
+
+#endif // LLVM_LIBC_SRC_STRING_STRLEN_H

libc/src/string/strlen.cpp

-//===-------------------- Implementation of strcpy -----------------------===//
+//===-------------------- Implementation of strlen ------------------------===//
 //
 // 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/string/strcpy.h"
+#include "src/string/strlen.h"
 
 #include "src/__support/common.h"
 
 namespace __llvm_libc {
 
-char *LLVM_LIBC_ENTRYPOINT(strcpy)(char *dest, const char *src) {
-  return reinterpret_cast<char *>(::memcpy(dest, src, ::strlen(src) + 1));
+// TODO: investigate the performance of this function.
+// There might be potential for compiler optmization.
+size_t LLVM_LIBC_ENTRYPOINT(strlen)(const char *src) {
+  const char *end = src;
+  while (*end != '\0')
+    ++end;
+  return end - src;
 }
 
 } // namespace __llvm_libc

libc/test/src/string/CMakeLists.txt

 add_libc_testsuite(libc_string_unittests)
 
 add_subdirectory(memory_utils)
 
 add_libc_unittest(
   strcat_test
   SUITE
     libc_string_unittests
   SRCS
     strcat_test.cpp
   DEPENDS
     strcat
     strcpy
+    strlen
 )
 
 add_libc_unittest(
   strcpy_test
   SUITE
     libc_string_unittests
   SRCS
     strcpy_test.cpp
   DEPENDS
     strcpy
+    strlen
+)
+
+add_libc_unittest(
+  strlen_test
+  SUITE
+    libc_string_unittests
+  SRCS
+    strlen_test.cpp
+  DEPENDS
+    strlen
 )
 
 # Tests all implementations of memcpy that can run on the host.
 get_property(memcpy_implementations GLOBAL PROPERTY memcpy_implementations)
 foreach(memcpy_config_name IN LISTS memcpy_implementations)
   get_target_property(require_cpu_features ${memcpy_config_name} REQUIRE_CPU_FEATURES)
   host_supports(can_run "${require_cpu_features}")
   if(can_run)

libc/test/src/string/strlen_test.cpp

+//===----------------------- Unittests for strlen -------------------------===//
+//
+// 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/string/strlen.h"
+#include "utils/UnitTest/Test.h"
+
+TEST(StrLenTest, EmptyString) {
+  const char *empty = "";
+
+  size_t result = __llvm_libc::strlen(empty);
+  ASSERT_EQ((size_t)0, result);
+}
+
+TEST(StrLenTest, AnyString) {
+  const char *any = "Hello World!";
+
+  size_t result = __llvm_libc::strlen(any);
+  ASSERT_EQ((size_t)12, result);
+}