// After editing this file, run "go generate" in the parent directory.

// Copyright 2020 The Wuffs Authors.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//    https://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

// ---------------- String Conversions

// wuffs_base__parse_number__foo_digits entries are 0x00 for invalid digits,
// and (0x80 | v) for valid digits, where v is the 4 bit value.

static const uint8_t wuffs_base__parse_number__decimal_digits[256] = {
    // 0     1     2     3     4     5     6     7
    // 8     9     A     B     C     D     E     F
    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,  // 0x00 ..= 0x07.
    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,  // 0x08 ..= 0x0F.
    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,  // 0x10 ..= 0x17.
    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,  // 0x18 ..= 0x1F.
    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,  // 0x20 ..= 0x27.
    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,  // 0x28 ..= 0x2F.
    0x80, 0x81, 0x82, 0x83, 0x84, 0x85, 0x86, 0x87,  // 0x30 ..= 0x37. '0'-'7'.
    0x88, 0x89, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,  // 0x38 ..= 0x3F. '8'-'9'.

    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,  // 0x40 ..= 0x47.
    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,  // 0x48 ..= 0x4F.
    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,  // 0x50 ..= 0x57.
    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,  // 0x58 ..= 0x5F.
    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,  // 0x60 ..= 0x67.
    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,  // 0x68 ..= 0x6F.
    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,  // 0x70 ..= 0x77.
    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,  // 0x78 ..= 0x7F.

    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,  // 0x80 ..= 0x87.
    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,  // 0x88 ..= 0x8F.
    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,  // 0x90 ..= 0x97.
    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,  // 0x98 ..= 0x9F.
    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,  // 0xA0 ..= 0xA7.
    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,  // 0xA8 ..= 0xAF.
    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,  // 0xB0 ..= 0xB7.
    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,  // 0xB8 ..= 0xBF.

    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,  // 0xC0 ..= 0xC7.
    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,  // 0xC8 ..= 0xCF.
    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,  // 0xD0 ..= 0xD7.
    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,  // 0xD8 ..= 0xDF.
    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,  // 0xE0 ..= 0xE7.
    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,  // 0xE8 ..= 0xEF.
    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,  // 0xF0 ..= 0xF7.
    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,  // 0xF8 ..= 0xFF.
    // 0     1     2     3     4     5     6     7
    // 8     9     A     B     C     D     E     F
};

static const uint8_t wuffs_base__parse_number__hexadecimal_digits[256] = {
    // 0     1     2     3     4     5     6     7
    // 8     9     A     B     C     D     E     F
    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,  // 0x00 ..= 0x07.
    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,  // 0x08 ..= 0x0F.
    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,  // 0x10 ..= 0x17.
    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,  // 0x18 ..= 0x1F.
    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,  // 0x20 ..= 0x27.
    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,  // 0x28 ..= 0x2F.
    0x80, 0x81, 0x82, 0x83, 0x84, 0x85, 0x86, 0x87,  // 0x30 ..= 0x37. '0'-'7'.
    0x88, 0x89, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,  // 0x38 ..= 0x3F. '8'-'9'.

    0x00, 0x8A, 0x8B, 0x8C, 0x8D, 0x8E, 0x8F, 0x00,  // 0x40 ..= 0x47. 'A'-'F'.
    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,  // 0x48 ..= 0x4F.
    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,  // 0x50 ..= 0x57.
    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,  // 0x58 ..= 0x5F.
    0x00, 0x8A, 0x8B, 0x8C, 0x8D, 0x8E, 0x8F, 0x00,  // 0x60 ..= 0x67. 'a'-'f'.
    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,  // 0x68 ..= 0x6F.
    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,  // 0x70 ..= 0x77.
    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,  // 0x78 ..= 0x7F.

    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,  // 0x80 ..= 0x87.
    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,  // 0x88 ..= 0x8F.
    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,  // 0x90 ..= 0x97.
    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,  // 0x98 ..= 0x9F.
    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,  // 0xA0 ..= 0xA7.
    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,  // 0xA8 ..= 0xAF.
    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,  // 0xB0 ..= 0xB7.
    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,  // 0xB8 ..= 0xBF.

    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,  // 0xC0 ..= 0xC7.
    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,  // 0xC8 ..= 0xCF.
    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,  // 0xD0 ..= 0xD7.
    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,  // 0xD8 ..= 0xDF.
    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,  // 0xE0 ..= 0xE7.
    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,  // 0xE8 ..= 0xEF.
    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,  // 0xF0 ..= 0xF7.
    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,  // 0xF8 ..= 0xFF.
    // 0     1     2     3     4     5     6     7
    // 8     9     A     B     C     D     E     F
};

// --------

WUFFS_BASE__MAYBE_STATIC wuffs_base__result_i64  //
wuffs_base__parse_number_i64(wuffs_base__slice_u8 s) {
  uint8_t* p = s.ptr;
  uint8_t* q = s.ptr + s.len;

  for (; (p < q) && (*p == '_'); p++) {
  }

  bool negative = false;
  if (p >= q) {
    goto fail_bad_argument;
  } else if (*p == '-') {
    p++;
    negative = true;
  } else if (*p == '+') {
    p++;
  }

  do {
    wuffs_base__result_u64 r = wuffs_base__parse_number_u64(
        wuffs_base__make_slice_u8(p, (size_t)(q - p)));
    if (r.status.repr != NULL) {
      wuffs_base__result_i64 ret;
      ret.status.repr = r.status.repr;
      ret.value = 0;
      return ret;
    } else if (negative) {
      if (r.value > 0x8000000000000000) {
        goto fail_out_of_bounds;
      }
      wuffs_base__result_i64 ret;
      ret.status.repr = NULL;
      ret.value = -(int64_t)(r.value);
      return ret;
    } else if (r.value > 0x7FFFFFFFFFFFFFFF) {
      goto fail_out_of_bounds;
    } else {
      wuffs_base__result_i64 ret;
      ret.status.repr = NULL;
      ret.value = +(int64_t)(r.value);
      return ret;
    }
  } while (0);

fail_bad_argument:
  do {
    wuffs_base__result_i64 ret;
    ret.status.repr = wuffs_base__error__bad_argument;
    ret.value = 0;
    return ret;
  } while (0);

fail_out_of_bounds:
  do {
    wuffs_base__result_i64 ret;
    ret.status.repr = wuffs_base__error__out_of_bounds;
    ret.value = 0;
    return ret;
  } while (0);
}

WUFFS_BASE__MAYBE_STATIC wuffs_base__result_u64  //
wuffs_base__parse_number_u64(wuffs_base__slice_u8 s) {
  uint8_t* p = s.ptr;
  uint8_t* q = s.ptr + s.len;

  for (; (p < q) && (*p == '_'); p++) {
  }

  if (p >= q) {
    goto fail_bad_argument;

  } else if (*p == '0') {
    p++;
    if (p >= q) {
      goto ok_zero;
    }
    if (*p == '_') {
      p++;
      for (; p < q; p++) {
        if (*p != '_') {
          goto fail_bad_argument;
        }
      }
      goto ok_zero;
    }

    if ((*p == 'x') || (*p == 'X')) {
      p++;
      for (; (p < q) && (*p == '_'); p++) {
      }
      if (p < q) {
        goto hexadecimal;
      }

    } else if ((*p == 'd') || (*p == 'D')) {
      p++;
      for (; (p < q) && (*p == '_'); p++) {
      }
      if (p < q) {
        goto decimal;
      }
    }

    goto fail_bad_argument;
  }

decimal:
  do {
    uint64_t v = wuffs_base__parse_number__decimal_digits[*p++];
    if (v == 0) {
      goto fail_bad_argument;
    }
    v &= 0x0F;

    // UINT64_MAX is 18446744073709551615, which is ((10 * max10) + max1).
    const uint64_t max10 = 1844674407370955161;
    const uint8_t max1 = 5;

    for (; p < q; p++) {
      if (*p == '_') {
        continue;
      }
      uint8_t digit = wuffs_base__parse_number__decimal_digits[*p];
      if (digit == 0) {
        goto fail_bad_argument;
      }
      digit &= 0x0F;
      if ((v > max10) || ((v == max10) && (digit > max1))) {
        goto fail_out_of_bounds;
      }
      v = (10 * v) + ((uint64_t)(digit));
    }

    wuffs_base__result_u64 ret;
    ret.status.repr = NULL;
    ret.value = v;
    return ret;
  } while (0);

hexadecimal:
  do {
    uint64_t v = wuffs_base__parse_number__hexadecimal_digits[*p++];
    if (v == 0) {
      goto fail_bad_argument;
    }
    v &= 0x0F;

    for (; p < q; p++) {
      if (*p == '_') {
        continue;
      }
      uint8_t digit = wuffs_base__parse_number__hexadecimal_digits[*p];
      if (digit == 0) {
        goto fail_bad_argument;
      }
      digit &= 0x0F;
      if ((v >> 60) != 0) {
        goto fail_out_of_bounds;
      }
      v = (v << 4) | ((uint64_t)(digit));
    }

    wuffs_base__result_u64 ret;
    ret.status.repr = NULL;
    ret.value = v;
    return ret;
  } while (0);

ok_zero:
  do {
    wuffs_base__result_u64 ret;
    ret.status.repr = NULL;
    ret.value = 0;
    return ret;
  } while (0);

fail_bad_argument:
  do {
    wuffs_base__result_u64 ret;
    ret.status.repr = wuffs_base__error__bad_argument;
    ret.value = 0;
    return ret;
  } while (0);

fail_out_of_bounds:
  do {
    wuffs_base__result_u64 ret;
    ret.status.repr = wuffs_base__error__out_of_bounds;
    ret.value = 0;
    return ret;
  } while (0);
}

// ---------------- Hexadecimal

WUFFS_BASE__MAYBE_STATIC size_t  //
wuffs_base__hexadecimal__decode2(wuffs_base__slice_u8 dst,
                                 wuffs_base__slice_u8 src) {
  size_t src_len2 = src.len / 2;
  size_t len = dst.len < src_len2 ? dst.len : src_len2;
  uint8_t* d = dst.ptr;
  uint8_t* s = src.ptr;
  size_t n = len;

  while (n--) {
    *d = (uint8_t)((wuffs_base__parse_number__hexadecimal_digits[s[0]] << 4) |
                   (wuffs_base__parse_number__hexadecimal_digits[s[1]] & 0x0F));
    d += 1;
    s += 2;
  }

  return len;
}

WUFFS_BASE__MAYBE_STATIC size_t  //
wuffs_base__hexadecimal__decode4(wuffs_base__slice_u8 dst,
                                 wuffs_base__slice_u8 src) {
  size_t src_len4 = src.len / 4;
  size_t len = dst.len < src_len4 ? dst.len : src_len4;
  uint8_t* d = dst.ptr;
  uint8_t* s = src.ptr;
  size_t n = len;

  while (n--) {
    *d = (uint8_t)((wuffs_base__parse_number__hexadecimal_digits[s[2]] << 4) |
                   (wuffs_base__parse_number__hexadecimal_digits[s[3]] & 0x0F));
    d += 1;
    s += 4;
  }

  return len;
}

// ---------------- Unicode and UTF-8

WUFFS_BASE__MAYBE_STATIC size_t  //
wuffs_base__utf_8__encode(wuffs_base__slice_u8 dst, uint32_t code_point) {
  if (code_point <= 0x7F) {
    if (dst.len >= 1) {
      dst.ptr[0] = (uint8_t)(code_point);
      return 1;
    }

  } else if (code_point <= 0x07FF) {
    if (dst.len >= 2) {
      dst.ptr[0] = (uint8_t)(0xC0 | ((code_point >> 6)));
      dst.ptr[1] = (uint8_t)(0x80 | ((code_point >> 0) & 0x3F));
      return 2;
    }

  } else if (code_point <= 0xFFFF) {
    if ((dst.len >= 3) && ((code_point < 0xD800) || (0xDFFF < code_point))) {
      dst.ptr[0] = (uint8_t)(0xE0 | ((code_point >> 12)));
      dst.ptr[1] = (uint8_t)(0x80 | ((code_point >> 6) & 0x3F));
      dst.ptr[2] = (uint8_t)(0x80 | ((code_point >> 0) & 0x3F));
      return 3;
    }

  } else if (code_point <= 0x10FFFF) {
    if (dst.len >= 4) {
      dst.ptr[0] = (uint8_t)(0xF0 | ((code_point >> 18)));
      dst.ptr[1] = (uint8_t)(0x80 | ((code_point >> 12) & 0x3F));
      dst.ptr[2] = (uint8_t)(0x80 | ((code_point >> 6) & 0x3F));
      dst.ptr[3] = (uint8_t)(0x80 | ((code_point >> 0) & 0x3F));
      return 4;
    }
  }

  return 0;
}

// wuffs_base__utf_8__byte_length_minus_1 is the byte length (minus 1) of a
// UTF-8 encoded code point, based on the encoding's initial byte.
//  - 0x00 is 1-byte UTF-8 (ASCII).
//  - 0x01 is the start of 2-byte UTF-8.
//  - 0x02 is the start of 3-byte UTF-8.
//  - 0x03 is the start of 4-byte UTF-8.
//  - 0x40 is a UTF-8 tail byte.
//  - 0x80 is invalid UTF-8.
//
// RFC 3629 (UTF-8) gives this grammar for valid UTF-8:
//    UTF8-1      = %x00-7F
//    UTF8-2      = %xC2-DF UTF8-tail
//    UTF8-3      = %xE0 %xA0-BF UTF8-tail / %xE1-EC 2( UTF8-tail ) /
//                  %xED %x80-9F UTF8-tail / %xEE-EF 2( UTF8-tail )
//    UTF8-4      = %xF0 %x90-BF 2( UTF8-tail ) / %xF1-F3 3( UTF8-tail ) /
//                  %xF4 %x80-8F 2( UTF8-tail )
//    UTF8-tail   = %x80-BF
static const uint8_t wuffs_base__utf_8__byte_length_minus_1[256] = {
    // 0     1     2     3     4     5     6     7
    // 8     9     A     B     C     D     E     F
    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,  // 0x00 ..= 0x07.
    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,  // 0x08 ..= 0x0F.
    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,  // 0x10 ..= 0x17.
    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,  // 0x18 ..= 0x1F.
    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,  // 0x20 ..= 0x27.
    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,  // 0x28 ..= 0x2F.
    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,  // 0x30 ..= 0x37.
    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,  // 0x38 ..= 0x3F.

    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,  // 0x40 ..= 0x47.
    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,  // 0x48 ..= 0x4F.
    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,  // 0x50 ..= 0x57.
    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,  // 0x58 ..= 0x5F.
    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,  // 0x60 ..= 0x67.
    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,  // 0x68 ..= 0x6F.
    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,  // 0x70 ..= 0x77.
    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,  // 0x78 ..= 0x7F.

    0x40, 0x40, 0x40, 0x40, 0x40, 0x40, 0x40, 0x40,  // 0x80 ..= 0x87.
    0x40, 0x40, 0x40, 0x40, 0x40, 0x40, 0x40, 0x40,  // 0x88 ..= 0x8F.
    0x40, 0x40, 0x40, 0x40, 0x40, 0x40, 0x40, 0x40,  // 0x90 ..= 0x97.
    0x40, 0x40, 0x40, 0x40, 0x40, 0x40, 0x40, 0x40,  // 0x98 ..= 0x9F.
    0x40, 0x40, 0x40, 0x40, 0x40, 0x40, 0x40, 0x40,  // 0xA0 ..= 0xA7.
    0x40, 0x40, 0x40, 0x40, 0x40, 0x40, 0x40, 0x40,  // 0xA8 ..= 0xAF.
    0x40, 0x40, 0x40, 0x40, 0x40, 0x40, 0x40, 0x40,  // 0xB0 ..= 0xB7.
    0x40, 0x40, 0x40, 0x40, 0x40, 0x40, 0x40, 0x40,  // 0xB8 ..= 0xBF.

    0x80, 0x80, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01,  // 0xC0 ..= 0xC7.
    0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01,  // 0xC8 ..= 0xCF.
    0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01,  // 0xD0 ..= 0xD7.
    0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01,  // 0xD8 ..= 0xDF.
    0x02, 0x02, 0x02, 0x02, 0x02, 0x02, 0x02, 0x02,  // 0xE0 ..= 0xE7.
    0x02, 0x02, 0x02, 0x02, 0x02, 0x02, 0x02, 0x02,  // 0xE8 ..= 0xEF.
    0x03, 0x03, 0x03, 0x03, 0x03, 0x80, 0x80, 0x80,  // 0xF0 ..= 0xF7.
    0x80, 0x80, 0x80, 0x80, 0x80, 0x80, 0x80, 0x80,  // 0xF8 ..= 0xFF.
    // 0     1     2     3     4     5     6     7
    // 8     9     A     B     C     D     E     F
};

WUFFS_BASE__MAYBE_STATIC wuffs_base__utf_8__next__output  //
wuffs_base__utf_8__next(wuffs_base__slice_u8 s) {
  if (s.len == 0) {
    return wuffs_base__make_utf_8__next__output(0, 0);
  }
  uint32_t c = s.ptr[0];
  switch (wuffs_base__utf_8__byte_length_minus_1[c & 0xFF]) {
    case 0:
      return wuffs_base__make_utf_8__next__output(c, 1);

    case 1:
      if (s.len < 2) {
        break;
      }
      c = wuffs_base__load_u16le__no_bounds_check(s.ptr);
      if ((c & 0xC000) != 0x8000) {
        break;
      }
      c = (0x0007C0 & (c << 6)) | (0x00003F & (c >> 8));
      return wuffs_base__make_utf_8__next__output(c, 2);

    case 2:
      if (s.len < 3) {
        break;
      }
      c = wuffs_base__load_u24le__no_bounds_check(s.ptr);
      if ((c & 0xC0C000) != 0x808000) {
        break;
      }
      c = (0x00F000 & (c << 12)) | (0x000FC0 & (c >> 2)) |
          (0x00003F & (c >> 16));
      if ((c <= 0x07FF) || ((0xD800 <= c) && (c <= 0xDFFF))) {
        break;
      }
      return wuffs_base__make_utf_8__next__output(c, 3);

    case 3:
      if (s.len < 4) {
        break;
      }
      c = wuffs_base__load_u32le__no_bounds_check(s.ptr);
      if ((c & 0xC0C0C000) != 0x80808000) {
        break;
      }
      c = (0x1C0000 & (c << 18)) | (0x03F000 & (c << 4)) |
          (0x000FC0 & (c >> 10)) | (0x00003F & (c >> 24));
      if ((c <= 0xFFFF) || (0x110000 <= c)) {
        break;
      }
      return wuffs_base__make_utf_8__next__output(c, 4);
  }

  return wuffs_base__make_utf_8__next__output(
      WUFFS_BASE__UNICODE_REPLACEMENT_CHARACTER, 1);
}

WUFFS_BASE__MAYBE_STATIC size_t  //
wuffs_base__utf_8__longest_valid_prefix(wuffs_base__slice_u8 s) {
  // TODO: possibly optimize the all-ASCII case (4 or 8 bytes at a time).
  //
  // TODO: possibly optimize this by manually inlining the
  // wuffs_base__utf_8__next calls.
  size_t original_len = s.len;
  while (s.len > 0) {
    wuffs_base__utf_8__next__output o = wuffs_base__utf_8__next(s);
    if ((o.code_point > 0x7F) && (o.byte_length == 1)) {
      break;
    }
    s.ptr += o.byte_length;
    s.len -= o.byte_length;
  }
  return original_len - s.len;
}

WUFFS_BASE__MAYBE_STATIC size_t  //
wuffs_base__ascii__longest_valid_prefix(wuffs_base__slice_u8 s) {
  // TODO: possibly optimize this by checking 4 or 8 bytes at a time.
  uint8_t* original_ptr = s.ptr;
  uint8_t* p = s.ptr;
  uint8_t* q = s.ptr + s.len;
  for (; (p != q) && ((*p & 0x80) == 0); p++) {
  }
  return (size_t)(p - original_ptr);
}