[libc] Templatize strstr

libc/src/string/CMakeLists.txt

 )
 
 add_entrypoint_object(
   strstr
   SRCS
     strstr.cpp
   HDRS
     strstr.h
+  DEPENDS
+    .memory_utils.strstr_implementation
 )
 
 add_entrypoint_object(
   strtok
   SRCS
     strtok.cpp
   HDRS
     strtok.h

libc/src/string/memory_utils/CMakeLists.txt

DEPS
     .memset_implementation
 )
 
 add_header_library(
   strcmp_implementation
   HDRS
     strcmp_implementations.h
 )
+
+add_header_library(
+  strstr_implementation
+  HDRS
+    strstr_implementations.h
+)

libc/src/string/memory_utils/strstr_implementations.h

+//===-- str{,case}str implementation ----------------------------*- C++ -*-===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_LIBC_SRC_STRING_MEMORY_UTILS_STRSTR_IMPLEMENTATIONS_H
+#define LLVM_LIBC_SRC_STRING_MEMORY_UTILS_STRSTR_IMPLEMENTATIONS_H
+
+#include <stddef.h>
+
+namespace __llvm_libc {
+
+template <typename Comp>
+constexpr static char *strstr_implementation(const char *haystack,
+                                             const char *needle, Comp &&comp) {
+  // TODO: This is a simple brute force implementation. This can be
+  // improved upon using well known string matching algorithms.
+  for (size_t i = 0; comp(haystack[i], 0); ++i) {
+    size_t j = 0;
+    for (; comp(haystack[i + j], 0) && !comp(haystack[i + j], needle[j]); ++j)
+      ;
+    if (!comp(needle[j], 0))
+      return const_cast<char *>(haystack + i);
+  }
+  return nullptr;
+}
+
+} // namespace __llvm_libc
+
+#endif // LLVM_LIBC_SRC_STRING_MEMORY_UTILS_STRSTR_IMPLEMENTATIONS_H

libc/src/string/strstr.cpp

 //===-- Implementation of strstr ------------------------------------------===//
 //
 // 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/strstr.h"
 
 #include "src/__support/common.h"
-#include <stddef.h>
+#include "src/string/memory_utils/strstr_implementations.h"
 
 namespace __llvm_libc {
 
 // TODO: This is a simple brute force implementation. This can be
 // improved upon using well known string matching algorithms.
 LLVM_LIBC_FUNCTION(char *, strstr, (const char *haystack, const char *needle)) {
-  for (size_t i = 0; haystack[i]; ++i) {
-    size_t j;
-    for (j = 0; haystack[i + j] && haystack[i + j] == needle[j]; ++j)
-      ;
-    if (!needle[j])
-      return const_cast<char *>(haystack + i);
-  }
-  return nullptr;
+  auto comp = [](char l, char r) -> int { return l - r; };
+  return strstr_implementation(haystack, needle, comp);
 }
 
 } // namespace __llvm_libc

utils/bazel/llvm-project-overlay/libc/BUILD.bazel

libc_support_library(
     textual_hdrs = [
         "src/string/memory_utils/bcmp_implementations.h",
         "src/string/memory_utils/bzero_implementations.h",
         "src/string/memory_utils/memcmp_implementations.h",
         "src/string/memory_utils/memcpy_implementations.h",
         "src/string/memory_utils/memmove_implementations.h",
         "src/string/memory_utils/memset_implementations.h",
         "src/string/memory_utils/strcmp_implementations.h",
+        "src/string/memory_utils/strstr_implementations.h",
     ],
     deps = [
         ":__support_common",
         ":__support_compiler_features",
         ":__support_cpp_array",
         ":__support_cpp_bit",
         ":__support_cpp_cstddef",
         ":__support_cpp_type_traits",

 )
 
 libc_function(
     name = "strstr",
     srcs = ["src/string/strstr.cpp"],
     hdrs = ["src/string/strstr.h"],
     deps = [
         ":__support_common",
+        ":string_memory_utils",
         ":string_utils",
     ],
 )
 
 libc_function(
     name = "strnlen",
     srcs = ["src/string/strnlen.cpp"],
     hdrs = ["src/string/strnlen.h"],