libc/src/string/memory_utils/inline_memmem.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_INLINE_MEMMEM_H
  10 #define LLVM_LIBC_SRC_STRING_MEMORY_UTILS_INLINE_MEMMEM_H
  11
  12 #include "src/__support/macros/attributes.h"
  13
  14 #include <stddef.h>
  15
  16 namespace LIBC_NAMESPACE {
  17
  18 template <typename Comp>
  19 LIBC_INLINE constexpr static void *
  20 inline_memmem(const void *haystack, size_t haystack_len, const void *needle,
  21               size_t needle_len, Comp &&comp) {
  22   // TODO: simple brute force implementation. This can be
  23   // improved upon using well known string matching algorithms.
  24   if (!needle_len)
  25     return const_cast<void *>(haystack);
  26
  27   if (needle_len > haystack_len)
  28     return nullptr;
  29
  30   const unsigned char *h = static_cast<const unsigned char *>(haystack);
  31   const unsigned char *n = static_cast<const unsigned char *>(needle);
  32   for (size_t i = 0; i <= (haystack_len - needle_len); ++i) {
  33     size_t j = 0;
  34     for (; j < needle_len && !comp(h[i + j], n[j]); ++j)
  35       ;
  36     if (j == needle_len)
  37       return const_cast<unsigned char *>(h + i);
  38   }
  39   return nullptr;
  40 }
  41
  42 } // namespace LIBC_NAMESPACE
  43
  44 #endif // LLVM_LIBC_SRC_STRING_MEMORY_UTILS_INLINE_MEMMEM_H