valid_utf32_to_latin1.h

#ifndef SIMDUTF_VALID_UTF32_TO_LATIN1_H
#define SIMDUTF_VALID_UTF32_TO_LATIN1_H
 
namespace simdutf {
namespace scalar {
namespace {
namespace utf32_to_latin1 {
 
template <typename ReadPtr, typename WritePtr>
simdutf_constexpr23 size_t convert_valid(ReadPtr data, size_t len,
                                         WritePtr latin1_output) {
  static_assert(
      std::is_same<typename std::decay<decltype(*data)>::type, uint32_t>::value,
      "dereferencing the data pointer must result in a uint32_t");
  auto start = latin1_output;
  uint32_t utf32_char;
  size_t pos = 0;
 
  while (pos < len) {
    utf32_char = data[pos];
 
#if SIMDUTF_CPLUSPLUS23
    // avoid using the 8 byte at a time optimization in constant evaluation
    // mode. memcpy can't be used and replacing it with bitwise or gave worse
    // codegen (when not during constant evaluation).
    if !consteval {
#endif
      if (pos + 2 <= len) {
        // if it is safe to read 8 more bytes, check that they are Latin1
        uint64_t v;
        std::memcpy(&v, data + pos, sizeof(uint64_t));
        if ((v & 0xFFFFFF00FFFFFF00) == 0) {
          *latin1_output++ = char(data[pos]);
          *latin1_output++ = char(data[pos + 1]);
          pos += 2;
          continue;
        } else {
          // output can not be represented in latin1
          return 0;
        }
      }
#if SIMDUTF_CPLUSPLUS23
    } // if ! consteval
#endif
    if ((utf32_char & 0xFFFFFF00) == 0) {
      *latin1_output++ = char(utf32_char);
    } else {
      // output can not be represented in latin1
      return 0;
    }
    pos++;
  }
  return latin1_output - start;
}
 
simdutf_really_inline size_t convert_valid(const char32_t *buf, size_t len,
                                           char *latin1_output) {
  return convert_valid(reinterpret_cast<const uint32_t *>(buf), len,
                       latin1_output);
}
 
} // namespace utf32_to_latin1
} // unnamed namespace
} // namespace scalar
} // namespace simdutf
 
#endif