valid_utf32_to_utf16.h

#ifndef SIMDUTF_VALID_UTF32_TO_UTF16_H
#define SIMDUTF_VALID_UTF32_TO_UTF16_H
 
namespace simdutf {
namespace scalar {
namespace {
namespace utf32_to_utf16 {
 
template <endianness big_endian>
simdutf_constexpr23 size_t convert_valid(const char32_t *data, size_t len,
                                         char16_t *utf16_output) {
  size_t pos = 0;
  char16_t *start{utf16_output};
  while (pos < len) {
    uint32_t word = data[pos];
    if ((word & 0xFFFF0000) == 0) {
      // will not generate a surrogate pair
      *utf16_output++ = !match_system(big_endian)
                            ? char16_t(u16_swap_bytes(uint16_t(word)))
                            : char16_t(word);
      pos++;
    } else {
      // will generate a surrogate pair
      word -= 0x10000;
      uint16_t high_surrogate = uint16_t(0xD800 + (word >> 10));
      uint16_t low_surrogate = uint16_t(0xDC00 + (word & 0x3FF));
      if simdutf_constexpr (!match_system(big_endian)) {
        high_surrogate = u16_swap_bytes(high_surrogate);
        low_surrogate = u16_swap_bytes(low_surrogate);
      }
      *utf16_output++ = char16_t(high_surrogate);
      *utf16_output++ = char16_t(low_surrogate);
      pos++;
    }
  }
  return utf16_output - start;
}
 
} // namespace utf32_to_utf16
} // unnamed namespace
} // namespace scalar
} // namespace simdutf
 
#endif