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 // Copyright 2018 - 2023 Ulf Adams
 // Copyright 2023 Matt Borland
 // Distributed under the Boost Software License, Version 1.0.
 // https://www.boost.org/LICENSE_1_0.txt
 
 #ifndef BOOST_CHARCONV_DETAIL_RYU_RYU_GENERIC_128_HPP
 #define BOOST_CHARCONV_DETAIL_RYU_RYU_GENERIC_128_HPP
 
 #include <boost/charconv/detail/ryu/generic_128.hpp>
 #include <boost/charconv/detail/integer_search_trees.hpp>
 #include <boost/charconv/detail/config.hpp>
 #include <boost/charconv/detail/bit_layouts.hpp>
 #include <boost/charconv/to_chars.hpp>
 #include <cinttypes>
 #include <cstdio>
 #include <cstdint>
 
 #ifdef BOOST_CHARCONV_DEBUG
 #  include <iostream>
 #endif
 
 namespace boost { namespace charconv { namespace detail { namespace ryu {
 
 static constexpr int32_t fd128_exceptional_exponent = 0x7FFFFFFF;
 static constexpr unsigned_128_type one = 1;
 
 struct floating_decimal_128
 {
     unsigned_128_type mantissa;
     int32_t exponent;
     bool sign;
 };
 
 #ifdef BOOST_CHARCONV_DEBUG
 static char* s(unsigned_128_type v) {
   int len = num_digits(v);
   char* b = static_cast<char*>(malloc((len + 1) * sizeof(char)));
   for (int i = 0; i < len; i++) {
     const uint32_t c = static_cast<uint32_t>(v % 10);
     v /= 10;
     b[len - 1 - i] = static_cast<char>('0' + c);
   }
   b[len] = 0;
   return b;
 }
 #endif
 
 static inline struct floating_decimal_128 generic_binary_to_decimal(
         const unsigned_128_type bits,
         const uint32_t mantissaBits, const uint32_t exponentBits, const bool explicitLeadingBit) noexcept
 {
     #ifdef BOOST_CHARCONV_DEBUG
     printf("IN=");
     for (int32_t bit = 127; bit >= 0; --bit)
     {
         printf("%u", static_cast<uint32_t>((bits >> bit) & 1));
     }
     printf("\n");
     #endif
 
     const uint32_t bias = (1u << (exponentBits - 1)) - 1;
     const bool ieeeSign = ((bits >> (mantissaBits + exponentBits)) & 1) != 0;
     const unsigned_128_type ieeeMantissa = bits & ((one << mantissaBits) - 1);
     const uint32_t ieeeExponent = static_cast<uint32_t>((bits >> mantissaBits) & ((one << exponentBits) - 1u));
 
     if (ieeeExponent == 0 && ieeeMantissa == 0)
     {
         struct floating_decimal_128 fd {0, 0, ieeeSign};
         return fd;
     }
     if (ieeeExponent == ((1u << exponentBits) - 1u))
     {
         struct floating_decimal_128 fd;
         fd.mantissa = explicitLeadingBit ? ieeeMantissa & ((one << (mantissaBits - 1)) - 1) : ieeeMantissa;
         fd.exponent = fd128_exceptional_exponent;
         fd.sign = ieeeSign;
         return fd;
     }
 
     int32_t e2;
     unsigned_128_type m2;
     // We subtract 2 in all cases so that the bounds computation has 2 additional bits.
     if (explicitLeadingBit)
     {
         // mantissaBits includes the explicit leading bit, so we need to correct for that here.
         if (ieeeExponent == 0)
         {
             e2 = static_cast<int32_t>(1 - bias - mantissaBits + 1 - 2);
         }
         else
         {
             e2 = static_cast<int32_t>(ieeeExponent - bias - mantissaBits + 1 - 2);
         }
         m2 = ieeeMantissa;
     }
     else
     {
         if (ieeeExponent == 0)
         {
             e2 = static_cast<int32_t>(1 - bias - mantissaBits - 2);
             m2 = ieeeMantissa;
         } else
         {
             e2 = static_cast<int32_t>(ieeeExponent - bias - mantissaBits - 2U);
             m2 = (one << mantissaBits) | ieeeMantissa;
         }
     }
     const bool even = (m2 & 1) == 0;
     const bool acceptBounds = even;
 
     #ifdef BOOST_CHARCONV_DEBUG
     printf("-> %s %s * 2^%d\n", ieeeSign ? "-" : "+", s(m2), e2 + 2);
     #endif
 
     // Step 2: Determine the interval of legal decimal representations.
     const unsigned_128_type mv = 4 * m2;
     // Implicit bool -> int conversion. True is 1, false is 0.
     const uint32_t mmShift =
             (ieeeMantissa != (explicitLeadingBit ? one << (mantissaBits - 1) : 0))
             || (ieeeExponent == 0);
 
     // Step 3: Convert to a decimal power base using 128-bit arithmetic.
     unsigned_128_type vr;
     unsigned_128_type vp;
     unsigned_128_type vm;
     int32_t e10;
     bool vmIsTrailingZeros = false;
     bool vrIsTrailingZeros = false;
     if (e2 >= 0)
     {
         // I tried special-casing q == 0, but there was no effect on performance.
         // This expression is slightly faster than max(0, log10Pow2(e2) - 1).
         const uint32_t q = log10Pow2(e2) - (e2 > 3);
         e10 = static_cast<int32_t>(q);
         const int32_t k = BOOST_CHARCONV_POW5_INV_BITCOUNT + static_cast<int32_t>(pow5bits(q)) - 1;
         const int32_t i = -e2 + static_cast<int32_t>(q) + k;
         uint64_t pow5[4];
         generic_computeInvPow5(q, pow5);
         vr = mulShift(4 * m2, pow5, i);
         vp = mulShift(4 * m2 + 2, pow5, i);
         vm = mulShift(4 * m2 - 1 - mmShift, pow5, i);
 
         #ifdef BOOST_CHARCONV_DEBUG
         printf("%s * 2^%d / 10^%d\n", s(mv), e2, q);
         printf("V+=%s\nV =%s\nV-=%s\n", s(vp), s(vr), s(vm));
         #endif
 
         // floor(log_5(2^128)) = 55, this is very conservative
         if (q <= 55)
         {
             // Only one of mp, mv, and mm can be a multiple of 5, if any.
             if (mv % 5 == 0)
             {
                 vrIsTrailingZeros = multipleOfPowerOf5(mv, q - 1);
             }
             else if (acceptBounds)
             {
                 // Same as min(e2 + (~mm & 1), pow5Factor(mm)) >= q
                 // <=> e2 + (~mm & 1) >= q && pow5Factor(mm) >= q
                 // <=> true && pow5Factor(mm) >= q, since e2 >= q.
                 vmIsTrailingZeros = multipleOfPowerOf5(mv - 1 - mmShift, q);
             }
             else
             {
                 // Same as min(e2 + 1, pow5Factor(mp)) >= q.
                 vp -= multipleOfPowerOf5(mv + 2, q);
             }
         }
     }
     else
     {
         // This expression is slightly faster than max(0, log10Pow5(-e2) - 1).
         const uint32_t q = log10Pow5(-e2) - static_cast<uint32_t>(-e2 > 1);
         e10 = static_cast<int32_t>(q) + e2;
         const int32_t i = -e2 - static_cast<int32_t>(q);
         const int32_t k = static_cast<int32_t>(pow5bits(static_cast<uint32_t>(i))) - BOOST_CHARCONV_POW5_BITCOUNT;
         const int32_t j = static_cast<int32_t>(q) - k;
         uint64_t pow5[4];
         generic_computePow5(static_cast<uint32_t>(i), pow5);
         vr = mulShift(4 * m2, pow5, j);
         vp = mulShift(4 * m2 + 2, pow5, j);
         vm = mulShift(4 * m2 - 1 - mmShift, pow5, j);
 
         #ifdef BOOST_CHARCONV_DEBUG
         printf("%s * 5^%d / 10^%d\n", s(mv), -e2, q);
         printf("%d %d %d %d\n", q, i, k, j);
         printf("V+=%s\nV =%s\nV-=%s\n", s(vp), s(vr), s(vm));
         #endif
 
         if (q <= 1)
         {
             // {vr,vp,vm} is trailing zeros if {mv,mp,mm} has at least q trailing 0 bits.
             // mv = 4 m2, so it always has at least two trailing 0 bits.
             vrIsTrailingZeros = true;
             if (acceptBounds)
             {
                 // mm = mv - 1 - mmShift, so it has 1 trailing 0 bit iff mmShift == 1.
                 vmIsTrailingZeros = mmShift == 1;
             }
             else
             {
                 // mp = mv + 2, so it always has at least one trailing 0 bit.
                 --vp;
             }
         }
         else if (q < 127)
         {
             // We need to compute min(ntz(mv), pow5Factor(mv) - e2) >= q-1
             // <=> ntz(mv) >= q-1  &&  pow5Factor(mv) - e2 >= q-1
             // <=> ntz(mv) >= q-1    (e2 is negative and -e2 >= q)
             // <=> (mv & ((1 << (q-1)) - 1)) == 0
             // We also need to make sure that the left shift does not overflow.
             vrIsTrailingZeros = multipleOfPowerOf2(mv, q - 1);
 
             #ifdef BOOST_CHARCONV_DEBUG
             printf("vr is trailing zeros=%s\n", vrIsTrailingZeros ? "true" : "false");
             #endif
         }
     }
 
     #ifdef BOOST_CHARCONV_DEBUG
     printf("e10=%d\n", e10);
     printf("V+=%s\nV =%s\nV-=%s\n", s(vp), s(vr), s(vm));
     printf("vm is trailing zeros=%s\n", vmIsTrailingZeros ? "true" : "false");
     printf("vr is trailing zeros=%s\n", vrIsTrailingZeros ? "true" : "false");
     #endif
 
     // Step 4: Find the shortest decimal representation in the interval of legal representations.
     uint32_t removed = 0;
     uint8_t lastRemovedDigit = 0;
     unsigned_128_type output;
 
     while (vp / 10 > vm / 10)
     {
         vmIsTrailingZeros &= vm % 10 == 0;
         vrIsTrailingZeros &= lastRemovedDigit == 0;
         lastRemovedDigit = static_cast<uint8_t>(vr % 10);
         vr /= 10;
         vp /= 10;
         vm /= 10;
         ++removed;
     }
 
     #ifdef BOOST_CHARCONV_DEBUG
     printf("V+=%s\nV =%s\nV-=%s\n", s(vp), s(vr), s(vm));
     printf("d-10=%s\n", vmIsTrailingZeros ? "true" : "false");
     #endif
 
     if (vmIsTrailingZeros)
     {
         while (vm % 10 == 0)
         {
             vrIsTrailingZeros &= lastRemovedDigit == 0;
             lastRemovedDigit = static_cast<uint8_t>(vr % 10);
             vr /= 10;
             vp /= 10;
             vm /= 10;
             ++removed;
         }
     }
 
     #ifdef BOOST_CHARCONV_DEBUG
     printf("%s %d\n", s(vr), lastRemovedDigit);
     printf("vr is trailing zeros=%s\n", vrIsTrailingZeros ? "true" : "false");
     #endif
 
     if (vrIsTrailingZeros && (lastRemovedDigit == 5) && (vr % 2 == 0))
     {
         // Round even if the exact numbers is .....50..0.
         lastRemovedDigit = 4;
     }
     // We need to take vr+1 if vr is outside bounds, or we need to round up.
     output = vr + static_cast<unsigned_128_type>((vr == vm && (!acceptBounds || !vmIsTrailingZeros)) || (lastRemovedDigit >= 5));
     const int32_t exp = e10 + static_cast<int32_t>(removed);
 
     #ifdef BOOST_CHARCONV_DEBUG
     printf("V+=%s\nV =%s\nV-=%s\n", s(vp), s(vr), s(vm));
     printf("O=%s\n", s(output));
     printf("EXP=%d\n", exp);
     #endif
 
     return {output, exp, ieeeSign};
 }
 
 static inline int copy_special_str(char* result, const std::ptrdiff_t result_size, const struct floating_decimal_128 fd) noexcept
 {
     if (fd.sign)
     {
         *result = '-';
         ++result;
     }
 
     if (fd.mantissa)
     {
         if (fd.sign)
         {
             if (fd.mantissa == static_cast<unsigned_128_type>(2305843009213693952) ||
                 fd.mantissa == static_cast<unsigned_128_type>(6917529027641081856) ||
                 fd.mantissa == static_cast<unsigned_128_type>(1) << 110) // 2^110
             {
                 if (result_size >= 10)
                 {
                     std::memcpy(result, "nan(snan)", 9);
                     return 10;
                 }
                 else
                 {
                     return -1;
                 }
             }
             else
             {
                 if (result_size >= 9)
                 {
                     std::memcpy(result, "nan(ind)", 8);
                     return 9;
                 }
                 else
                 {
                     return -1;
                 }
             }
         }
         else
         {
             if (fd.mantissa == static_cast<unsigned_128_type>(2305843009213693952) ||
                 fd.mantissa == static_cast<unsigned_128_type>(6917529027641081856) ||
                 fd.mantissa == static_cast<unsigned_128_type>(1) << 110) // 2^110
             {
                 if (result_size >= 9)
                 {
                     std::memcpy(result, "nan(snan)", 9);
                     return 9;
                 }
                 else
                 {
                     return -1;
                 }
             }
             else
             {
                 if (result_size >= 3)
                 {
                     std::memcpy(result, "nan", 3);
                     return 3;
                 }
                 else
                 {
                     return -1;
                 }
             }
         }
     }
 
     if (result_size >= 3 + static_cast<std::ptrdiff_t>(fd.sign))
     {
         memcpy(result, "inf", 3);
         return static_cast<int>(fd.sign) + 3;
     }
 
     return -1;
 }
 
 static inline int generic_to_chars_fixed(const struct floating_decimal_128 v, char* result, const ptrdiff_t result_size, int precision) noexcept
 {
     if (v.exponent == fd128_exceptional_exponent)
     {
         return copy_special_str(result, result_size, v);
     }
 
     // Step 5: Print the decimal representation.
     if (v.sign)
     {
         *result++ = '-';
     }
 
     unsigned_128_type output = v.mantissa;
     const auto r = to_chars_128integer_impl(result, result + result_size, output);
     if (r.ec != std::errc())
     {
         return -static_cast<int>(r.ec);
     }
 
     auto current_len = static_cast<int>(r.ptr - result);
 
     #ifdef BOOST_CHARCONV_DEBUG
     char* man_print = s(v.mantissa);
     std::cerr << "Exp: " << v.exponent
               << "\nMantissa: " << man_print
               << "\nMan len: " << current_len << std::endl;
     free(man_print);
     #endif
 
     if (v.exponent == 0)
     {
         // Option 1: We need to do nothing
         return current_len + static_cast<int>(v.sign);
     }
     else if (v.exponent > 0)
     {
         // Option 2: Append 0s to the end of the number until we get the proper significand value
         // Then we need precison worth of zeros after the decimal point as applicable
         if (current_len + v.exponent > result_size)
         {
             return -static_cast<int>(std::errc::value_too_large);
         }
 
         result = r.ptr;
         memset(result, '0', static_cast<std::size_t>(v.exponent));
         result += static_cast<std::size_t>(v.exponent);
         current_len += v.exponent;
         *result++ = '.';
         ++precision;
     }
     else if ((-v.exponent) < current_len)
     {
         // Option 3: Insert a decimal point into the middle of the existing number
         if (current_len + v.exponent + 1 > result_size)
         {
             return -static_cast<int>(std::errc::result_out_of_range);
         }
 
         memmove(result + current_len + v.exponent + 1, result + current_len + v.exponent, static_cast<std::size_t>(-v.exponent));
         memcpy(result + current_len + v.exponent, ".", 1U);
         ++current_len;
         precision -= current_len + v.exponent;
         result += current_len + v.exponent + 1;
     }
     else
     {
         // Option 4: Leading 0s
         if (-v.exponent + 2 > result_size)
         {
             return -static_cast<int>(std::errc::value_too_large);
         }
 
         memmove(result - v.exponent - current_len + 2, result, static_cast<std::size_t>(current_len));
         memcpy(result, "0.", 2U);
         memset(result + 2, '0', static_cast<std::size_t>(0 - v.exponent - current_len));
         current_len = -v.exponent + 2;
         precision -= current_len - 2;
         result += current_len;
     }
 
     if (precision > 0)
     {
         if (current_len + precision > result_size)
         {
             return -static_cast<int>(std::errc::result_out_of_range);
         }
 
         memset(result, '0', static_cast<std::size_t>(precision));
         current_len += precision;
     }
 
     return current_len + static_cast<int>(v.sign);
 }
 
 // Converts the given decimal floating point number to a string, writing to result, and returning
 // the number characters written. Does not terminate the buffer with a 0. In the worst case, this
 // function can write up to 53 characters.
 //
 // Maximal char buffer requirement:
 // sign + mantissa digits + decimal dot + 'E' + exponent sign + exponent digits
 // = 1 + 39 + 1 + 1 + 1 + 10 = 53
 static inline int generic_to_chars(const struct floating_decimal_128 v, char* result, const ptrdiff_t result_size, 
                                    chars_format fmt = chars_format::general, int precision = -1) noexcept
 {
     if (v.exponent == fd128_exceptional_exponent)
     {
         return copy_special_str(result, result_size, v);
     }
 
     unsigned_128_type output = v.mantissa;
     const uint32_t olength = static_cast<uint32_t>(num_digits(output));
 
     #ifdef BOOST_CHARCONV_DEBUG
     printf("DIGITS=%s\n", s(v.mantissa));
     printf("OLEN=%u\n", olength);
     printf("EXP=%u\n", v.exponent + olength);
     #endif
 
     // See: https://github.com/cppalliance/charconv/issues/64
     if (fmt == chars_format::general)
     {
         const int64_t exp = v.exponent + static_cast<int64_t>(olength);
         if (std::abs(exp) <= olength)
         {
             return generic_to_chars_fixed(v, result, result_size, precision);
         }
     }
 
     // Step 5: Print the decimal representation.
     size_t index = 0;
     if (v.sign)
     {
         result[index++] = '-';
     }
 
     if (index + olength > static_cast<size_t>(result_size))
     {
         return -static_cast<int>(std::errc::value_too_large);
     }
     else if (olength == 0)
     {
         return -2; // Something has gone horribly wrong
     }
 
     for (uint32_t i = 0; i < olength - 1; ++i)
     {
         const auto c = static_cast<uint32_t>(output % 10);
         output /= 10;
         result[index + olength - i] = static_cast<char>('0' + c);
     }
     BOOST_CHARCONV_ASSERT(output < 10);
     result[index] = static_cast<char>('0' + static_cast<uint32_t>(output % 10)); // output should be < 10 by now.
 
     // Print decimal point if needed.
     if (olength > 1)
     {
         result[index + 1] = '.';
         index += olength + 1;
     }
     else
     {
         ++index;
     }
 
     // Reset the index to where the required precision should be
     if (precision != -1)
     {
         if (static_cast<size_t>(precision) < index)
         {
             if (fmt != chars_format::scientific)
             {
                 index = static_cast<size_t>(precision) + 1 + static_cast<size_t>(v.sign); // Precision is number of characters not just the decimal portion
             }
             else
             {
                 index = static_cast<size_t>(precision) + 2 + static_cast<size_t>(v.sign); // In scientific format the precision is just the decimal places
             }
 
             // Now we need to see if we need to round
             if (result[index] >= '5' && index < olength + 1 + static_cast<size_t>(v.sign))
             {
                 bool continue_rounding = false;
                 auto current_index = index;
                 do
                 {
                     --current_index;
                     if (result[current_index] == '9')
                     {
                         continue_rounding = true;
                         result[current_index] = '0';
                     }
                     else
                     {
                         continue_rounding = false;
                         result[current_index] = static_cast<char>(result[current_index] + static_cast<char>(1));
                     }
                 } while (continue_rounding && current_index > 2);
             }
 
             // If the last digit is a zero than overwrite that as well, but not in scientific formatting
             if (fmt != chars_format::scientific)
             {
                 while (result[index - 1] == '0')
                 {
                     --index;
                 }
             }
             else
             {
                 // In scientific formatting we may need a final 0 to achieve the correct precision
                 if (precision + 1 > static_cast<int>(olength))
                 {
                     result[index - 1] = '0';
                 }
             }
         }
         else if (static_cast<size_t>(precision) > index)
         {
             // Use our fallback routine that will capture more of the precision
             return -1;
         }
     }
 
     // Print the exponent.
     result[index++] = 'e';
     int32_t exp = v.exponent + static_cast<int32_t>(olength) - 1;
     if (exp < 0)
     {
         result[index++] = '-';
         exp = -exp;
     }
     else
     {
         result[index++] = '+';
     }
 
     uint32_t elength = static_cast<uint32_t>(num_digits(exp));
     for (uint32_t i = 0; i < elength; ++i)
     {
         // Always print a minimum of 2 characters in the exponent field
         if (elength == 1)
         {
             result[index + elength - 1 - i] = '0';
             ++index;
         }
 
         const uint32_t c = static_cast<uint32_t>(exp % 10);
         exp /= 10;
         result[index + elength - 1 - i] = static_cast<char>('0' + c);
     }
     if (elength == 0)
     {
         result[index++] = '0';
         result[index++] = '0';
     }
     
     index += elength;
     return static_cast<int>(index);
 }
 
 static inline struct floating_decimal_128 float_to_fd128(float f) noexcept
 {
     static_assert(sizeof(float) == sizeof(uint32_t), "Float is not 32 bits");
     uint32_t bits = 0;
     std::memcpy(&bits, &f, sizeof(float));
     return generic_binary_to_decimal(bits, 23, 8, false);
 }
 
 static inline struct floating_decimal_128 double_to_fd128(double d) noexcept
 {
     static_assert(sizeof(double) == sizeof(uint64_t), "Double is not 64 bits");
     uint64_t bits = 0;
     std::memcpy(&bits, &d, sizeof(double));
     return generic_binary_to_decimal(bits, 52, 11, false);
 }
 
 // https://en.cppreference.com/w/cpp/types/floating-point#Fixed_width_floating-point_types
 
 #ifdef BOOST_CHARCONV_HAS_FLOAT16
 
 static inline struct floating_decimal_128 float16_t_to_fd128(std::float16_t f) noexcept
 {
     uint16_t bits = 0;
     std::memcpy(&bits, &f, sizeof(std::float16_t));
     return generic_binary_to_decimal(bits, 10, 5, false);
 }
 
 #endif
 
 #ifdef BOOST_CHARCONV_HAS_BRAINFLOAT16
 
 static inline struct floating_decimal_128 float16_t_to_fd128(std::bfloat16_t f) noexcept
 {
     uint16_t bits = 0;
     std::memcpy(&bits, &f, sizeof(std::bfloat16_t));
     return generic_binary_to_decimal(bits, 7, 8, false);
 }
 
 #endif
 
 #if BOOST_CHARCONV_LDBL_BITS == 80
 
 static inline struct floating_decimal_128 long_double_to_fd128(long double d) noexcept
 {
     #ifdef BOOST_CHARCONV_HAS_INT128
     unsigned_128_type bits = 0;
     std::memcpy(&bits, &d, sizeof(long double));
     #else
     trivial_uint128 trivial_bits;
     std::memcpy(&trivial_bits, &d, sizeof(long double));
     unsigned_128_type bits {trivial_bits};
     #endif
 
     #ifdef BOOST_CHARCONV_DEBUG
     // For some odd reason, this ends up with noise in the top 48 bits. We can
     // clear out those bits with the following line; this is not required, the
     // conversion routine should ignore those bits, but the debug output can be
     // confusing if they aren't 0s.
     bits &= (one << 80) - 1;
     #endif
 
     return generic_binary_to_decimal(bits, 64, 15, true);
 }
 
 #elif BOOST_CHARCONV_LDBL_BITS == 128
 
 static inline struct floating_decimal_128 long_double_to_fd128(long double d) noexcept
 {
     unsigned_128_type bits = 0;
     std::memcpy(&bits, &d, sizeof(long double));
 
     #if LDBL_MANT_DIG == 113 // binary128 (e.g. ARM, S390X, PPC64LE)
     # ifdef __PPC64__
         return generic_binary_to_decimal(bits, 112, 15, false);
     # else
         return generic_binary_to_decimal(bits, 112, 15, true);
     # endif
     #elif LDBL_MANT_DIG == 106 // ibm128 (e.g. PowerPC)
     return generic_binary_to_decimal(bits, 105, 11, true);
     #endif
 }
 
 #endif
 
 }}}} // Namespaces
 
 #endif //BOOST_RYU_GENERIC_128_HPP

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