Method PrefixAccel_FrontAndBack

extern/re2/re2/prog.cc:943–986

#endif

const void* Prog::PrefixAccel_FrontAndBack(const void* data, size_t size) {
  DCHECK_GE(prefix_size_, 2);
  if (size < prefix_size_)
    return NULL;
  // Don't bother searching the last prefix_size_-1 bytes for prefix_front_.
  // This also means that probing for prefix_back_ doesn't go out of bounds.
  size -= prefix_size_-1;

#if defined(__AVX2__)
  // Use AVX2 to look for prefix_front_ and prefix_back_ 32 bytes at a time.
  if (size >= sizeof(__m256i)) {
    const __m256i* fp = reinterpret_cast<const __m256i*>(
        reinterpret_cast<const char*>(data));
    const __m256i* bp = reinterpret_cast<const __m256i*>(
        reinterpret_cast<const char*>(data) + prefix_size_-1);
    const __m256i* endfp = fp + size/sizeof(__m256i);
    const __m256i f_set1 = _mm256_set1_epi8(prefix_front_);
    const __m256i b_set1 = _mm256_set1_epi8(prefix_back_);
    while (fp != endfp) {
      const __m256i f_loadu = _mm256_loadu_si256(fp++);
      const __m256i b_loadu = _mm256_loadu_si256(bp++);
      const __m256i f_cmpeq = _mm256_cmpeq_epi8(f_set1, f_loadu);
      const __m256i b_cmpeq = _mm256_cmpeq_epi8(b_set1, b_loadu);
      const int fb_testz = _mm256_testz_si256(f_cmpeq, b_cmpeq);
      if (fb_testz == 0) {  // ZF: 1 means zero, 0 means non-zero.
        const __m256i fb_and = _mm256_and_si256(f_cmpeq, b_cmpeq);
        const int fb_movemask = _mm256_movemask_epi8(fb_and);
        const int fb_ctz = FindLSBSet(fb_movemask);
        return reinterpret_cast<const char*>(fp-1) + fb_ctz;
      }
    }
    data = fp;
    size = size%sizeof(__m256i);
  }
#endif

  const char* p0 = reinterpret_cast<const char*>(data);
  for (const char* p = p0;; p++) {
    DCHECK_GE(size, static_cast<size_t>(p-p0));
    p = reinterpret_cast<const char*>(memchr(p, prefix_front_, size - (p-p0)));
    if (p == NULL || p[prefix_size_-1] == prefix_back_)
      return p;
  }
}

}  // namespace re2