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 // Copyright 2020-2023 Daniel Lemire
 // Copyright 2023 Matt Borland
 // Distributed under the Boost Software License, Version 1.0.
 // https://www.boost.org/LICENSE_1_0.txt
 //
 // Derivative of: https://github.com/fastfloat/fast_float
 
 #ifndef BOOST_CHARCONV_DETAIL_FASTFLOAT_ASCII_NUMBER_HPP
 #define BOOST_CHARCONV_DETAIL_FASTFLOAT_ASCII_NUMBER_HPP
 
 #include <boost/charconv/detail/fast_float/float_common.hpp>
 #include <cctype>
 #include <cstdint>
 #include <cstring>
 #include <iterator>
 
 namespace boost { namespace charconv { namespace detail { namespace fast_float {
 
 // Next function can be micro-optimized, but compilers are entirely
 // able to optimize it well.
 template <typename UC>
 BOOST_FORCEINLINE constexpr bool is_integer(UC c) noexcept {
   return !(c > UC('9') || c < UC('0'));
 }
 
 BOOST_FORCEINLINE constexpr uint64_t byteswap(uint64_t val) {
   return (val & 0xFF00000000000000) >> 56
     | (val & 0x00FF000000000000) >> 40
     | (val & 0x0000FF0000000000) >> 24
     | (val & 0x000000FF00000000) >> 8
     | (val & 0x00000000FF000000) << 8
     | (val & 0x0000000000FF0000) << 24
     | (val & 0x000000000000FF00) << 40
     | (val & 0x00000000000000FF) << 56;
 }
 
 BOOST_FORCEINLINE BOOST_CHARCONV_FASTFLOAT_CONSTEXPR20
 uint64_t read_u64(const char *chars) {
   if (cpp20_and_in_constexpr()) {
     uint64_t val = 0;
     for(int i = 0; i < 8; ++i) {
       val |= uint64_t(*chars) << (i*8);
       ++chars;
     }
     return val;
   }
   uint64_t val;
   ::memcpy(&val, chars, sizeof(uint64_t));
 #if BOOST_CHARCONV_FASTFLOAT_IS_BIG_ENDIAN == 1
   // Need to read as-if the number was in little-endian order.
   val = byteswap(val);
 #endif
   return val;
 }
 
 BOOST_FORCEINLINE BOOST_CHARCONV_FASTFLOAT_CONSTEXPR20
 void write_u64(uint8_t *chars, uint64_t val) {
   if (cpp20_and_in_constexpr()) {
     for(int i = 0; i < 8; ++i) {
       *chars = uint8_t(val);
       val >>= 8;
       ++chars;
     }
     return;
   }
 #if BOOST_CHARCONV_FASTFLOAT_IS_BIG_ENDIAN == 1
   // Need to read as-if the number was in little-endian order.
   val = byteswap(val);
 #endif
   ::memcpy(chars, &val, sizeof(uint64_t));
 }
 
 // credit  @aqrit
 BOOST_FORCEINLINE BOOST_CHARCONV_FASTFLOAT_CONSTEXPR14
 uint32_t parse_eight_digits_unrolled(uint64_t val) {
   constexpr uint64_t mask = 0x000000FF000000FF;
   constexpr uint64_t mul1 = 0x000F424000000064; // 100 + (1000000ULL << 32)
   constexpr uint64_t mul2 = 0x0000271000000001; // 1 + (10000ULL << 32)
   val -= 0x3030303030303030;
   val = (val * 10) + (val >> 8); // val = (val * 2561) >> 8;
   val = (((val & mask) * mul1) + (((val >> 16) & mask) * mul2)) >> 32;
   return uint32_t(val);
 }
 
 BOOST_FORCEINLINE constexpr
 uint32_t parse_eight_digits_unrolled(const char16_t *)  noexcept  {
   return 0;
 }
 
 BOOST_FORCEINLINE constexpr
 uint32_t parse_eight_digits_unrolled(const char32_t *)  noexcept  {
   return 0;
 }
 
 BOOST_FORCEINLINE BOOST_CHARCONV_FASTFLOAT_CONSTEXPR20
 uint32_t parse_eight_digits_unrolled(const char *chars)  noexcept  {
   return parse_eight_digits_unrolled(read_u64(chars));
 }
 
 // credit @aqrit
 BOOST_FORCEINLINE constexpr bool is_made_of_eight_digits_fast(uint64_t val)  noexcept  {
   return !((((val + 0x4646464646464646) | (val - 0x3030303030303030)) & 0x8080808080808080));
 }
 
 BOOST_FORCEINLINE constexpr
 bool is_made_of_eight_digits_fast(const char16_t *)  noexcept  {
   return false;
 }
 
 BOOST_FORCEINLINE constexpr
 bool is_made_of_eight_digits_fast(const char32_t *)  noexcept  {
   return false;
 }
 
 BOOST_FORCEINLINE BOOST_CHARCONV_FASTFLOAT_CONSTEXPR20
 bool is_made_of_eight_digits_fast(const char *chars)  noexcept  {
   return is_made_of_eight_digits_fast(read_u64(chars));
 }
 
 template <typename UC>
 struct parsed_number_string_t {
   int64_t exponent{0};
   uint64_t mantissa{0};
   UC const * lastmatch{nullptr};
   bool negative{false};
   bool valid{false};
   bool too_many_digits{false};
   // contains the range of the significant digits
   span<const UC> integer{};  // non-nullable
   span<const UC> fraction{}; // nullable
 };
 using byte_span = span<char>;
 using parsed_number_string = parsed_number_string_t<char>;
 // Assuming that you use no more than 19 digits, this will
 // parse an ASCII string.
 template <typename UC>
 BOOST_FORCEINLINE BOOST_CHARCONV_FASTFLOAT_CONSTEXPR20
 parsed_number_string_t<UC> parse_number_string(UC const *p, UC const * pend, parse_options_t<UC> options) noexcept {
   chars_format const fmt = options.format;
   UC const decimal_point = options.decimal_point;
 
   parsed_number_string_t<UC> answer;
   answer.valid = false;
   answer.too_many_digits = false;
   answer.negative = (*p == UC('-'));
 #ifdef BOOST_CHARCONV_FASTFLOAT_ALLOWS_LEADING_PLUS // disabled by default
   if ((*p == UC('-')) || (*p == UC('+')))
 #else
   if (*p == UC('-')) // C++17 20.19.3.(7.1) explicitly forbids '+' sign here
 #endif
   {
     ++p;
     if (p == pend) {
       return answer;
     }
     if (!is_integer(*p) && (*p != decimal_point)) { // a sign must be followed by an integer or the dot
       return answer;
     }
   }
   UC const * const start_digits = p;
 
   uint64_t i = 0; // an unsigned int avoids signed overflows (which are bad)
 
   while ((p != pend) && is_integer(*p)) {
     // a multiplication by 10 is cheaper than an arbitrary integer
     // multiplication
     i = 10 * i +
         uint64_t(*p - UC('0')); // might overflow, we will handle the overflow later
     ++p;
   }
   UC const * const end_of_integer_part = p;
   int64_t digit_count = int64_t(end_of_integer_part - start_digits);
   answer.integer = span<const UC>(start_digits, size_t(digit_count));
   int64_t exponent = 0;
   if ((p != pend) && (*p == decimal_point)) {
     ++p;
     UC const * before = p;
     // can occur at most twice without overflowing, but let it occur more, since
     // for integers with many digits, digit parsing is the primary bottleneck.
     if (std::is_same<UC,char>::value) {
       while ((std::distance(p, pend) >= 8) && is_made_of_eight_digits_fast(p)) {
         i = i * 100000000 + parse_eight_digits_unrolled(p); // in rare cases, this will overflow, but that's ok
         p += 8;
       }
     }
     while ((p != pend) && is_integer(*p)) {
       uint8_t digit = uint8_t(*p - UC('0'));
       ++p;
       i = i * 10 + digit; // in rare cases, this will overflow, but that's ok
     }
     exponent = before - p;
     answer.fraction = span<const UC>(before, size_t(p - before));
     digit_count -= exponent;
   }
   // we must have encountered at least one integer!
   if (digit_count == 0) {
     return answer;
   }
   int64_t exp_number = 0;            // explicit exponential part
   if ((static_cast<unsigned>(fmt) & static_cast<unsigned>(chars_format::scientific)) && (p != pend) && ((UC('e') == *p) || (UC('E') == *p))) {
     UC const * location_of_e = p;
     ++p;
     bool neg_exp = false;
     if ((p != pend) && (UC('-') == *p)) {
       neg_exp = true;
       ++p;
     } else if ((p != pend) && (UC('+') == *p)) { // '+' on exponent is allowed by C++17 20.19.3.(7.1)
       ++p;
     }
     if ((p == pend) || !is_integer(*p)) {
       if(!(static_cast<unsigned>(fmt) & static_cast<unsigned>(chars_format::fixed))) {
         // We are in error.
         return answer;
       }
       // Otherwise, we will be ignoring the 'e'.
       p = location_of_e;
     } else {
       while ((p != pend) && is_integer(*p)) {
         uint8_t digit = uint8_t(*p - UC('0'));
         if (exp_number < 0x10000000) {
           exp_number = 10 * exp_number + digit;
         }
         ++p;
       }
       if(neg_exp) { exp_number = - exp_number; }
       exponent += exp_number;
     }
   } else {
     // If it scientific and not fixed, we have to bail out.
     if((static_cast<unsigned>(fmt) & static_cast<unsigned>(chars_format::scientific)) &&
        !(static_cast<unsigned>(fmt) & static_cast<unsigned>(chars_format::fixed)))
     {
         return answer;
     }
   }
   answer.lastmatch = p;
   answer.valid = true;
 
   // If we frequently had to deal with long strings of digits,
   // we could extend our code by using a 128-bit integer instead
   // of a 64-bit integer. However, this is uncommon.
   //
   // We can deal with up to 19 digits.
   if (digit_count > 19) { // this is uncommon
     // It is possible that the integer had an overflow.
     // We have to handle the case where we have 0.0000somenumber.
     // We need to be mindful of the case where we only have zeroes...
     // E.g., 0.000000000...000.
     UC const * start = start_digits;
     while ((start != pend) && (*start == UC('0') || *start == decimal_point)) {
       if(*start == UC('0')) { digit_count --; }
       start++;
     }
     if (digit_count > 19) {
       answer.too_many_digits = true;
       // Let us start again, this time, avoiding overflows.
       // We don't need to check if is_integer, since we use the
       // pre-tokenized spans from above.
       i = 0;
       p = answer.integer.ptr;
       UC const * int_end = p + answer.integer.len();
       constexpr uint64_t minimal_nineteen_digit_integer{1000000000000000000};
       while((i < minimal_nineteen_digit_integer) && (p != int_end)) {
         i = i * 10 + uint64_t(*p - UC('0'));
         ++p;
       }
       if (i >= minimal_nineteen_digit_integer) { // We have a big integers
         exponent = end_of_integer_part - p + exp_number;
       } else { // We have a value with a fractional component.
           p = answer.fraction.ptr;
           UC const * frac_end = p + answer.fraction.len();
           while((i < minimal_nineteen_digit_integer) && (p != frac_end)) {
             i = i * 10 + uint64_t(*p - UC('0'));
             ++p;
           }
           exponent = answer.fraction.ptr - p + exp_number;
       }
       // We have now corrected both exponent and i, to a truncated value
     }
   }
   answer.exponent = exponent;
   answer.mantissa = i;
   return answer;
 }
 
 }}}} // namespace s
 
 #endif

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