[libc][wchar] implement wcslen (#124150)

Update string_utils' string_length to work with char* or wchar_t*, so that it
may be reusable when implementing wmemchr, wcspbrk, wcsrchr, wcsstr.

Link: #121183
Link: #124027

Co-authored-by: Nick Desaulniers <ndesaulniers@google.com>

---------

Co-authored-by: Tristan Ross <tristan.ross@midstall.com>

2 files changed, 12 insertions, 12 deletions

diff --git a/libc/src/string/CMakeLists.txt b/libc/src/string/CMakeLists.txt
index e3faa543e630..2c607bf8ea89 100644
--- a/libc/src/string/CMakeLists.txt
+++ b/libc/src/string/CMakeLists.txt
@@ -17,9 +17,11 @@ add_header_library(
   DEPENDS
     .memory_utils.inline_bzero
     .memory_utils.inline_memcpy
+    libc.hdr.types.size_t
     libc.include.stdlib
-    libc.src.__support.common
     libc.src.__support.CPP.bitset
+    libc.src.__support.CPP.type_traits
+    libc.src.__support.common
   ${string_config_options}
 )
 
diff --git a/libc/src/string/string_utils.h b/libc/src/string/string_utils.h
index fc617bd18e8f..583d35014d39 100644
--- a/libc/src/string/string_utils.h
+++ b/libc/src/string/string_utils.h
@@ -14,12 +14,13 @@
 #ifndef LLVM_LIBC_SRC_STRING_STRING_UTILS_H
 #define LLVM_LIBC_SRC_STRING_STRING_UTILS_H
 
+#include "hdr/types/size_t.h"
 #include "src/__support/CPP/bitset.h"
+#include "src/__support/CPP/type_traits.h" // cpp::is_same_v
 #include "src/__support/macros/config.h"
 #include "src/__support/macros/optimization.h" // LIBC_UNLIKELY
 #include "src/string/memory_utils/inline_bzero.h"
 #include "src/string/memory_utils/inline_memcpy.h"
-#include <stddef.h> // For size_t
 
 namespace LIBC_NAMESPACE_DECL {
 namespace internal {
@@ -79,24 +80,21 @@ LIBC_INLINE size_t string_length_wide_read(const char *src) {
   return char_ptr - src;
 }
 
-LIBC_INLINE size_t string_length_byte_read(const char *src) {
-  size_t length;
-  for (length = 0; *src; ++src, ++length)
-    ;
-  return length;
-}
-
 // Returns the length of a string, denoted by the first occurrence
 // of a null terminator.
-LIBC_INLINE size_t string_length(const char *src) {
+template <typename T> LIBC_INLINE size_t string_length(const T *src) {
 #ifdef LIBC_COPT_STRING_UNSAFE_WIDE_READ
   // Unsigned int is the default size for most processors, and on x86-64 it
   // performs better than larger sizes when the src pointer can't be assumed to
   // be aligned to a word boundary, so it's the size we use for reading the
   // string a block at a time.
-  return string_length_wide_read<unsigned int>(src);
+  if constexpr (cpp::is_same_v<T, char>)
+    return string_length_wide_read<unsigned int>(src);
 #else
-  return string_length_byte_read(src);
+  size_t length;
+  for (length = 0; *src; ++src, ++length)
+    ;
+  return length;
 #endif
 }