bool FloatToSink()

in absl/strings/internal/str_format/float_conversion.cc [1305:1396]
76 lines of code
30 McCabe index (conditional complexity)

bool FloatToSink(const Float v, const FormatConversionSpecImpl &conv,
                 FormatSinkImpl *sink) {
  // Print the sign or the sign column.
  Float abs_v = v;
  char sign_char = 0;
  if (std::signbit(abs_v)) {
    sign_char = '-';
    abs_v = -abs_v;
  } else if (conv.has_show_pos_flag()) {
    sign_char = '+';
  } else if (conv.has_sign_col_flag()) {
    sign_char = ' ';
  }

  // Print nan/inf.
  if (ConvertNonNumericFloats(sign_char, abs_v, conv, sink)) {
    return true;
  }

  int precision = conv.precision() < 0 ? 6 : conv.precision();

  int exp = 0;

  auto decomposed = Decompose(abs_v);

  Buffer buffer;

  FormatConversionChar c = conv.conversion_char();

  if (c == FormatConversionCharInternal::f ||
      c == FormatConversionCharInternal::F) {
    FormatF(decomposed.mantissa, decomposed.exponent,
            {sign_char, precision, conv, sink});
    return true;
  } else if (c == FormatConversionCharInternal::e ||
             c == FormatConversionCharInternal::E) {
    if (!FloatToBuffer<FormatStyle::Precision>(decomposed, precision, &buffer,
                                               &exp)) {
      return FallbackToSnprintf(v, conv, sink);
    }
    if (!conv.has_alt_flag() && buffer.back() == '.') buffer.pop_back();
    PrintExponent(
        exp, FormatConversionCharIsUpper(conv.conversion_char()) ? 'E' : 'e',
        &buffer);
  } else if (c == FormatConversionCharInternal::g ||
             c == FormatConversionCharInternal::G) {
    precision = std::max(0, precision - 1);
    if (!FloatToBuffer<FormatStyle::Precision>(decomposed, precision, &buffer,
                                               &exp)) {
      return FallbackToSnprintf(v, conv, sink);
    }
    if (precision + 1 > exp && exp >= -4) {
      if (exp < 0) {
        // Have 1.23456, needs 0.00123456
        // Move the first digit
        buffer.begin[1] = *buffer.begin;
        // Add some zeros
        for (; exp < -1; ++exp) *buffer.begin-- = '0';
        *buffer.begin-- = '.';
        *buffer.begin = '0';
      } else if (exp > 0) {
        // Have 1.23456, needs 1234.56
        // Move the '.' exp positions to the right.
        std::rotate(buffer.begin + 1, buffer.begin + 2, buffer.begin + exp + 2);
      }
      exp = 0;
    }
    if (!conv.has_alt_flag()) {
      while (buffer.back() == '0') buffer.pop_back();
      if (buffer.back() == '.') buffer.pop_back();
    }
    if (exp) {
      PrintExponent(
          exp, FormatConversionCharIsUpper(conv.conversion_char()) ? 'E' : 'e',
          &buffer);
    }
  } else if (c == FormatConversionCharInternal::a ||
             c == FormatConversionCharInternal::A) {
    bool uppercase = (c == FormatConversionCharInternal::A);
    FormatA(HexFloatTypeParams(Float{}), decomposed.mantissa,
            decomposed.exponent, uppercase, {sign_char, precision, conv, sink});
    return true;
  } else {
    return false;
  }

  WriteBufferToSink(sign_char,
                    absl::string_view(buffer.begin, buffer.end - buffer.begin),
                    conv, sink);

  return true;
}