libc/src/string/memory_utils/memmem_implementations.h

   1 //===-- memmem implementation -----------------------------------*- C++ -*-===//
   2 //
   3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
   4 // See https://llvm.org/LICENSE.txt for license information.
   5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   6 //
   7 //===----------------------------------------------------------------------===//
   8
   9 #ifndef LLVM_LIBC_SRC_STRING_MEMORY_UTILS_MEMMEM_IMPLEMENTATIONS_H
  10 #define LLVM_LIBC_SRC_STRING_MEMORY_UTILS_MEMMEM_IMPLEMENTATIONS_H
  11
  12 #include <stddef.h>
  13
  14 namespace __llvm_libc {
  15
  16 template <typename Comp>
  17 constexpr static void *
  18 memmem_implementation(const void *haystack, size_t haystack_len,
  19                       const void *needle, size_t needle_len, Comp &&comp) {
  20   // TODO: simple brute force implementation. This can be
  21   // improved upon using well known string matching algorithms.
  22   if (!needle_len)
  23     return const_cast<void *>(haystack);
  24
  25   if (needle_len > haystack_len)
  26     return nullptr;
  27
  28   const unsigned char *h = static_cast<const unsigned char *>(haystack);
  29   const unsigned char *n = static_cast<const unsigned char *>(needle);
  30   for (size_t i = 0; i <= (haystack_len - needle_len); ++i) {
  31     size_t j = 0;
  32     for (; j < needle_len && !comp(h[i + j], n[j]); ++j)
  33       ;
  34     if (j == needle_len)
  35       return const_cast<unsigned char *>(h + i);
  36   }
  37   return nullptr;
  38 }
  39
  40 } // namespace __llvm_libc
  41
  42 #endif // LLVM_LIBC_SRC_STRING_MEMORY_UTILS_MEMMEM_IMPLEMENTATIONS_H