#if SIMDUTF_FEATURE_UTF16
template <simdutf_ByteFlip bflip>
simdutf_really_inline static result
rvv_utf16_to_latin1_with_errors(const char16_t *src, size_t len, char *dst) {
  const char16_t *const beg = src;
  for (size_t vl; len > 0; len -= vl, src += vl, dst += vl) {
    vl = __riscv_vsetvl_e16m8(len);
    vuint16m8_t v = __riscv_vle16_v_u16m8((uint16_t *)src, vl);
    v = simdutf_byteflip<bflip>(v, vl);
    long idx = __riscv_vfirst_m_b2(__riscv_vmsgtu_vx_u16m8_b2(v, 255, vl), vl);
    if (idx >= 0)
      return result(error_code::TOO_LARGE, src - beg + idx);
    __riscv_vse8_v_u8m4((uint8_t *)dst, __riscv_vncvt_x_x_w_u8m4(v, vl), vl);
  }
  return result(error_code::SUCCESS, src - beg);
}
#endif // SIMDUTF_FEATURE_UTF16

#if SIMDUTF_FEATURE_UTF16 && SIMDUTF_FEATURE_LATIN1
simdutf_warn_unused size_t implementation::convert_utf16le_to_latin1(
    const char16_t *src, size_t len, char *dst) const noexcept {
  result res = convert_utf16le_to_latin1_with_errors(src, len, dst);
  return res.error == error_code::SUCCESS ? res.count : 0;
}

simdutf_warn_unused size_t implementation::convert_utf16be_to_latin1(
    const char16_t *src, size_t len, char *dst) const noexcept {
  result res = convert_utf16be_to_latin1_with_errors(src, len, dst);
  return res.error == error_code::SUCCESS ? res.count : 0;
}

simdutf_warn_unused result
implementation::convert_utf16le_to_latin1_with_errors(
    const char16_t *src, size_t len, char *dst) const noexcept {
  return rvv_utf16_to_latin1_with_errors<simdutf_ByteFlip::NONE>(src, len, dst);
}

simdutf_warn_unused result
implementation::convert_utf16be_to_latin1_with_errors(
    const char16_t *src, size_t len, char *dst) const noexcept {
  if (supports_zvbb())
    return rvv_utf16_to_latin1_with_errors<simdutf_ByteFlip::ZVBB>(src, len,
                                                                   dst);
  else
    return rvv_utf16_to_latin1_with_errors<simdutf_ByteFlip::V>(src, len, dst);
}

simdutf_warn_unused size_t implementation::convert_valid_utf16le_to_latin1(
    const char16_t *src, size_t len, char *dst) const noexcept {
  const char16_t *const beg = src;
  for (size_t vl; len > 0; len -= vl, src += vl, dst += vl) {
    vl = __riscv_vsetvl_e16m8(len);
    vuint16m8_t v = __riscv_vle16_v_u16m8((uint16_t *)src, vl);
    __riscv_vse8_v_u8m4((uint8_t *)dst, __riscv_vncvt_x_x_w_u8m4(v, vl), vl);
  }
  return src - beg;
}

simdutf_warn_unused size_t implementation::convert_valid_utf16be_to_latin1(
    const char16_t *src, size_t len, char *dst) const noexcept {
  const char16_t *const beg = src;
  for (size_t vl; len > 0; len -= vl, src += vl, dst += vl) {
    vl = __riscv_vsetvl_e16m8(len);
    vuint16m8_t v = __riscv_vle16_v_u16m8((uint16_t *)src, vl);
    __riscv_vse8_v_u8m4((uint8_t *)dst, __riscv_vnsrl_wx_u8m4(v, 8, vl), vl);
  }
  return src - beg;
}
#endif // SIMDUTF_FEATURE_UTF16 && SIMDUTF_FEATURE_LATIN1

#if SIMDUTF_FEATURE_UTF8 && SIMDUTF_FEATURE_UTF16
template <simdutf_ByteFlip bflip>
simdutf_really_inline static result
rvv_utf16_to_utf8_with_errors(const char16_t *src, size_t len, char *dst) {
  size_t n = len;
  const char16_t *srcBeg = src;
  const char *dstBeg = dst;
  size_t vl8m4 = __riscv_vsetvlmax_e8m4();
  vbool2_t m4mulp2 = __riscv_vmseq_vx_u8m4_b2(
      __riscv_vand_vx_u8m4(__riscv_vid_v_u8m4(vl8m4), 3, vl8m4), 2, vl8m4);

  for (size_t vl, vlOut; n > 0;) {
    vl = __riscv_vsetvl_e16m2(n);

    vuint16m2_t v = __riscv_vle16_v_u16m2((uint16_t const *)src, vl);
    v = simdutf_byteflip<bflip>(v, vl);
    vbool8_t m234 = __riscv_vmsgtu_vx_u16m2_b8(v, 0x80 - 1, vl);

    if (__riscv_vfirst_m_b8(m234, vl) < 0) { /* 1 byte utf8 */
      vlOut = vl;
      __riscv_vse8_v_u8m1((uint8_t *)dst, __riscv_vncvt_x_x_w_u8m1(v, vlOut),
                          vlOut);
      n -= vl, src += vl, dst += vlOut;
      continue;
    }

    vbool8_t m34 = __riscv_vmsgtu_vx_u16m2_b8(v, 0x800 - 1, vl);

    if (__riscv_vfirst_m_b8(m34, vl) < 0) { /* 1/2 byte utf8 */
      /* 0: [     aaa|aabbbbbb]
       * 1: [aabbbbbb|        ] vsll 8
       * 2: [        |   aaaaa] vsrl 6
       * 3: [00111111|00011111]
       * 4: [  bbbbbb|000aaaaa] (1|2)&3
       * 5: [11000000|11000000]
       * 6: [10bbbbbb|110aaaaa] 4|5 */
      vuint16m2_t twoByte = __riscv_vand_vx_u16m2(
          __riscv_vor_vv_u16m2(__riscv_vsll_vx_u16m2(v, 8, vl),
                               __riscv_vsrl_vx_u16m2(v, 6, vl), vl),
          0b0011111100011111, vl);
      vuint16m2_t vout16 =
          __riscv_vor_vx_u16m2_mu(m234, v, twoByte, 0b1000000011000000, vl);
      vuint8m2_t vout = __riscv_vreinterpret_v_u16m2_u8m2(vout16);

      /* Every high byte that is zero should be compressed
       * low bytes should never be compressed, so we set them
       * to all ones, and then create a non-zero bytes mask */
      vbool4_t mcomp =
          __riscv_vmsne_vx_u8m2_b4(__riscv_vreinterpret_v_u16m2_u8m2(
                                       __riscv_vor_vx_u16m2(vout16, 0xFF, vl)),
                                   0, vl * 2);
      vlOut = __riscv_vcpop_m_b4(mcomp, vl * 2);

      vout = __riscv_vcompress_vm_u8m2(vout, mcomp, vl * 2);
      __riscv_vse8_v_u8m2((uint8_t *)dst, vout, vlOut);

      n -= vl, src += vl, dst += vlOut;
      continue;
    }

    vbool8_t sur = __riscv_vmseq_vx_u16m2_b8(
        __riscv_vand_vx_u16m2(v, 0xF800, vl), 0xD800, vl);
    long first = __riscv_vfirst_m_b8(sur, vl);
    size_t tail = vl - first;
    vl = first < 0 ? vl : first;

    if (vl > 0) { /* 1/2/3 byte utf8 */
      /* in: [aaaabbbb|bbcccccc]
       * v1: [0bcccccc|        ] vsll  8
       * v1: [10cccccc|        ] vsll  8 & 0b00111111 | 0b10000000
       * v2: [        |110bbbbb] vsrl  6 & 0b00111111 | 0b11000000
       * v2: [        |10bbbbbb] vsrl  6 & 0b00111111 | 0b10000000
       * v3: [        |1110aaaa] vsrl 12 | 0b11100000
       *  1: [00000000|0bcccccc|00000000|00000000] => [0bcccccc]
       *  2: [00000000|10cccccc|110bbbbb|00000000] => [110bbbbb] [10cccccc]
       *  3: [00000000|10cccccc|10bbbbbb|1110aaaa] => [1110aaaa] [10bbbbbb]
       * [10cccccc]
       */
      vuint16m2_t v1, v2, v3, v12;
      v1 = __riscv_vor_vx_u16m2_mu(
          m234, v, __riscv_vand_vx_u16m2(v, 0b00111111, vl), 0b10000000, vl);
      v1 = __riscv_vsll_vx_u16m2(v1, 8, vl);

      v2 = __riscv_vor_vx_u16m2(
          __riscv_vand_vx_u16m2(__riscv_vsrl_vx_u16m2(v, 6, vl), 0b00111111,
                                vl),
          0b10000000, vl);
      v2 = __riscv_vor_vx_u16m2_mu(__riscv_vmnot_m_b8(m34, vl), v2, v2,
                                   0b01000000, vl);
      v3 = __riscv_vor_vx_u16m2(__riscv_vsrl_vx_u16m2(v, 12, vl), 0b11100000,
                                vl);
      v12 = __riscv_vor_vv_u16m2_mu(m234, v1, v1, v2, vl);

      vuint32m4_t w12 = __riscv_vwmulu_vx_u32m4(v12, 1 << 8, vl);
      vuint32m4_t w123 = __riscv_vwaddu_wv_u32m4_mu(m34, w12, w12, v3, vl);
      vuint8m4_t vout = __riscv_vreinterpret_v_u32m4_u8m4(w123);

      vbool2_t mcomp = __riscv_vmor_mm_b2(
          m4mulp2, __riscv_vmsne_vx_u8m4_b2(vout, 0, vl * 4), vl * 4);
      vlOut = __riscv_vcpop_m_b2(mcomp, vl * 4);

      vout = __riscv_vcompress_vm_u8m4(vout, mcomp, vl * 4);
      __riscv_vse8_v_u8m4((uint8_t *)dst, vout, vlOut);

      n -= vl, src += vl, dst += vlOut;
    }

    if (tail)
      while (n) {
        uint16_t word = simdutf_byteflip<bflip>(src[0]);
        if ((word & 0xFF80) == 0) {
          break;
        } else if ((word & 0xF800) == 0) {
          break;
        } else if ((word & 0xF800) != 0xD800) {
          break;
        } else {
          // must be a surrogate pair
          if (n <= 1)
            return result(error_code::SURROGATE, src - srcBeg);
          uint16_t diff = word - 0xD800;
          if (diff > 0x3FF)
            return result(error_code::SURROGATE, src - srcBeg);
          uint16_t diff2 = simdutf_byteflip<bflip>(src[1]) - 0xDC00;
          if (diff2 > 0x3FF)
            return result(error_code::SURROGATE, src - srcBeg);

          uint32_t value = ((diff + 0x40) << 10) + diff2;

          // will generate four UTF-8 bytes
          // we have 0b11110XXX 0b10XXXXXX 0b10XXXXXX 0b10XXXXXX
          *dst++ = (char)((value >> 18) | 0b11110000);
          *dst++ = (char)(((value >> 12) & 0b111111) | 0b10000000);
          *dst++ = (char)(((value >> 6) & 0b111111) | 0b10000000);
          *dst++ = (char)((value & 0b111111) | 0b10000000);
          src += 2;
          n -= 2;
        }
      }
  }

  return result(error_code::SUCCESS, dst - dstBeg);
}

simdutf_warn_unused size_t implementation::convert_utf16le_to_utf8(
    const char16_t *src, size_t len, char *dst) const noexcept {
  result res = convert_utf16le_to_utf8_with_errors(src, len, dst);
  return res.error == error_code::SUCCESS ? res.count : 0;
}

simdutf_warn_unused size_t implementation::convert_utf16be_to_utf8(
    const char16_t *src, size_t len, char *dst) const noexcept {
  result res = convert_utf16be_to_utf8_with_errors(src, len, dst);
  return res.error == error_code::SUCCESS ? res.count : 0;
}

simdutf_warn_unused result implementation::convert_utf16le_to_utf8_with_errors(
    const char16_t *src, size_t len, char *dst) const noexcept {
  return rvv_utf16_to_utf8_with_errors<simdutf_ByteFlip::NONE>(src, len, dst);
}

simdutf_warn_unused result implementation::convert_utf16be_to_utf8_with_errors(
    const char16_t *src, size_t len, char *dst) const noexcept {
  if (supports_zvbb())
    return rvv_utf16_to_utf8_with_errors<simdutf_ByteFlip::ZVBB>(src, len, dst);
  else
    return rvv_utf16_to_utf8_with_errors<simdutf_ByteFlip::V>(src, len, dst);
}

simdutf_warn_unused size_t implementation::convert_valid_utf16le_to_utf8(
    const char16_t *src, size_t len, char *dst) const noexcept {
  return convert_utf16le_to_utf8(src, len, dst);
}

simdutf_warn_unused size_t implementation::convert_valid_utf16be_to_utf8(
    const char16_t *src, size_t len, char *dst) const noexcept {
  return convert_utf16be_to_utf8(src, len, dst);
}
#endif // SIMDUTF_FEATURE_UTF8 && SIMDUTF_FEATURE_UTF16

#if SIMDUTF_FEATURE_UTF16 && SIMDUTF_FEATURE_UTF32
template <simdutf_ByteFlip bflip>
simdutf_really_inline static result
rvv_utf16_to_utf32_with_errors(const char16_t *src, size_t len, char32_t *dst) {
  const char16_t *const srcBeg = src;
  char32_t *const dstBeg = dst;

  constexpr const uint16_t ANY_SURROGATE_MASK = 0xf800;
  constexpr const uint16_t ANY_SURROGATE_VALUE = 0xd800;
  constexpr const uint16_t LO_SURROGATE_MASK = 0xfc00;
  constexpr const uint16_t LO_SURROGATE_VALUE = 0xdc00;
  constexpr const uint16_t HI_SURROGATE_MASK = 0xfc00;
  constexpr const uint16_t HI_SURROGATE_VALUE = 0xd800;

  uint16_t last = 0;
  while (len > 0) {
    size_t vl = __riscv_vsetvl_e16m2(len);
    vuint16m2_t v0 = __riscv_vle16_v_u16m2((uint16_t const *)src, vl);
    v0 = simdutf_byteflip<bflip>(v0, vl);

    { // check fast-path
      const vuint16m2_t v = __riscv_vand_vx_u16m2(v0, ANY_SURROGATE_MASK, vl);
      const vbool8_t any_surrogate =
          __riscv_vmseq_vx_u16m2_b8(v, ANY_SURROGATE_VALUE, vl);
      if (__riscv_vfirst_m_b8(any_surrogate, vl) < 0) {
        /* no surrogates */
        __riscv_vse32_v_u32m4((uint32_t *)dst, __riscv_vzext_vf2_u32m4(v0, vl),
                              vl);
        len -= vl;
        src += vl;
        dst += vl;
        continue;
      }
    }

    if ((simdutf_byteflip<bflip>(src[0]) & LO_SURROGATE_MASK) ==
        LO_SURROGATE_VALUE) {
      return result(error_code::SURROGATE, src - srcBeg);
    }

    // decode surrogates
    vuint16m2_t v1 = __riscv_vslide1down_vx_u16m2(v0, 0, vl);
    vl = __riscv_vsetvl_e16m2(vl - 1);
    if (vl == 0) {
      return result(error_code::SURROGATE, src - srcBeg);
    }

    const vbool8_t surhi = __riscv_vmseq_vx_u16m2_b8(
        __riscv_vand_vx_u16m2(v0, HI_SURROGATE_MASK, vl), HI_SURROGATE_VALUE,
        vl);
    const vbool8_t surlo = __riscv_vmseq_vx_u16m2_b8(
        __riscv_vand_vx_u16m2(v1, LO_SURROGATE_MASK, vl), LO_SURROGATE_VALUE,
        vl);

    // compress everything but lo surrogates
    const vbool8_t compress = __riscv_vmsne_vx_u16m2_b8(
        __riscv_vand_vx_u16m2(v0, LO_SURROGATE_MASK, vl), LO_SURROGATE_VALUE,
        vl);

    {
      const vbool8_t diff = __riscv_vmxor_mm_b8(surhi, surlo, vl);
      const long idx = __riscv_vfirst_m_b8(diff, vl);
      if (idx >= 0) {
        uint16_t word = simdutf_byteflip<bflip>(src[idx]);
        if (word < 0xD800 || word > 0xDBFF) {
          return result(error_code::SURROGATE, src - srcBeg + idx + 1);
        }
        return result(error_code::SURROGATE, src - srcBeg + idx);
      }
    }

    last = simdutf_byteflip<bflip>(src[vl]);
    vuint32m4_t utf32 = __riscv_vzext_vf2_u32m4(v0, vl);

    // v0 = 110110yyyyyyyyyy (0xd800 + yyyyyyyyyy) --- hi surrogate
    // v1 = 110111xxxxxxxxxx (0xdc00 + xxxxxxxxxx) --- lo surrogate

    // t0 = u16(                    0000_00yy_yyyy_yyyy)
    const vuint32m4_t t0 =
        __riscv_vzext_vf2_u32m4(__riscv_vand_vx_u16m2(v0, 0x03ff, vl), vl);
    // t1 = u32(0000_0000_0000_yyyy_yyyy_yy00_0000_0000)
    const vuint32m4_t t1 = __riscv_vsll_vx_u32m4(t0, 10, vl);

    // t2 = u32(0000_0000_0000_0000_0000_00xx_xxxx_xxxx)
    const vuint32m4_t t2 =
        __riscv_vzext_vf2_u32m4(__riscv_vand_vx_u16m2(v1, 0x03ff, vl), vl);

    // t3 = u32(0000_0000_0000_yyyy_yyyy_yyxx_xxxx_xxxx)
    const vuint32m4_t t3 = __riscv_vor_vv_u32m4(t1, t2, vl);

    // t4 = utf32 from surrogate pairs
    const vuint32m4_t t4 = __riscv_vadd_vx_u32m4(t3, 0x10000, vl);

    const vuint32m4_t result = __riscv_vmerge_vvm_u32m4(utf32, t4, surhi, vl);

    const vuint32m4_t comp = __riscv_vcompress_vm_u32m4(result, compress, vl);
    const size_t vlOut = __riscv_vcpop_m_b8(compress, vl);
    __riscv_vse32_v_u32m4((uint32_t *)dst, comp, vlOut);

    len -= vl;
    src += vl;
    dst += vlOut;

    if ((last & LO_SURROGATE_MASK) == LO_SURROGATE_VALUE) {
      // last item is lo surrogate and got already consumed
      len -= 1;
      src += 1;
    }
  }

  return result(error_code::SUCCESS, dst - dstBeg);
}

simdutf_warn_unused size_t implementation::convert_utf16le_to_utf32(
    const char16_t *src, size_t len, char32_t *dst) const noexcept {
  result res = convert_utf16le_to_utf32_with_errors(src, len, dst);
  return res.error == error_code::SUCCESS ? res.count : 0;
}

simdutf_warn_unused size_t implementation::convert_utf16be_to_utf32(
    const char16_t *src, size_t len, char32_t *dst) const noexcept {
  result res = convert_utf16be_to_utf32_with_errors(src, len, dst);
  return res.error == error_code::SUCCESS ? res.count : 0;
}

simdutf_warn_unused result implementation::convert_utf16le_to_utf32_with_errors(
    const char16_t *src, size_t len, char32_t *dst) const noexcept {
  return rvv_utf16_to_utf32_with_errors<simdutf_ByteFlip::NONE>(src, len, dst);
}

simdutf_warn_unused result implementation::convert_utf16be_to_utf32_with_errors(
    const char16_t *src, size_t len, char32_t *dst) const noexcept {
  if (supports_zvbb())
    return rvv_utf16_to_utf32_with_errors<simdutf_ByteFlip::ZVBB>(src, len,
                                                                  dst);
  else
    return rvv_utf16_to_utf32_with_errors<simdutf_ByteFlip::V>(src, len, dst);
}

simdutf_warn_unused size_t implementation::convert_valid_utf16le_to_utf32(
    const char16_t *src, size_t len, char32_t *dst) const noexcept {
  return convert_utf16le_to_utf32(src, len, dst);
}

simdutf_warn_unused size_t implementation::convert_valid_utf16be_to_utf32(
    const char16_t *src, size_t len, char32_t *dst) const noexcept {
  return convert_utf16be_to_utf32(src, len, dst);
}
#endif // SIMDUTF_FEATURE_UTF16 && SIMDUTF_FEATURE_UTF32