String search with memchr() and memcmp()

find.c

#include <string.h>

static char* find(const char* haystackBegin, const char* haystackEnd, const char* needleBegin, const char* needleEnd)
{
  if (haystackEnd == NULL)
    haystackEnd = haystackBegin + strlen(haystackBegin);

  if (needleEnd == NULL)
    needleEnd = needleBegin + strlen(needleBegin);

  size_t haystackLength = haystackEnd - haystackBegin;
  size_t needleLength = needleEnd - needleBegin;

  if (haystackLength < needleLength)
    return NULL;

  if (needleBegin == needleEnd)
    return (char*)haystackBegin;

  if (needleLength == 1)
    return memchr(haystackBegin, needleBegin[0], haystackLength);

  while ((haystackBegin = (const char*)memchr(haystackBegin, needleBegin[0], haystackLength)) != NULL)
  {
    haystackLength = (size_t)(haystackEnd - haystackBegin);
    if (haystackLength == 0 || haystackLength < needleLength)
      return NULL;

    if (haystackBegin[needleLength - 1] == needleBegin[needleLength - 1])
    {
      if (needleLength == 2 || memcmp(haystackBegin + 1, needleBegin + 1, needleLength - 2) == 0)
        return (char*)haystackBegin;
    }

    ++haystackBegin;
    --haystackLength;
  }

  return NULL;
}

Thanks for the suggestion! I added your code into my benchmark: https://github.com/fenbf/articles/blob/master/cpp17/searchers/searchers.cpp (there's an example test run output at the bottom)