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 // Tencent is pleased to support the open source community by making RapidJSON available.
 //
 // Copyright (C) 2015 THL A29 Limited, a Tencent company, and Milo Yip.
 //
 // Licensed under the MIT License (the "License"); you may not use this file except
 // in compliance with the License. You may obtain a copy of the License at
 //
 // http://opensource.org/licenses/MIT
 //
 // 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.
  
 // This is a C++ header-only implementation of Grisu2 algorithm from the publication:
 // Loitsch, Florian. "Printing floating-point numbers quickly and accurately with
 // integers." ACM Sigplan Notices 45.6 (2010): 233-243.
  
 #ifndef RAPIDJSON_DTOA_
 #define RAPIDJSON_DTOA_
  
 #include "itoa.h" // GetDigitsLut()
 #include "diyfp.h"
 #include "ieee754.h"
  
 RAPIDJSON_NAMESPACE_BEGIN
 namespace internal {
  
 #ifdef __GNUC__
 RAPIDJSON_DIAG_PUSH
 RAPIDJSON_DIAG_OFF(effc++)
 RAPIDJSON_DIAG_OFF(array - bounds) // some gcc versions generate wrong warnings
                                    // https://gcc.gnu.org/bugzilla/show_bug.cgi?id=59124
 #endif
  
 inline void
 GrisuRound(char* buffer, int len, uint64_t delta, uint64_t rest, uint64_t ten_kappa, uint64_t wp_w)
 {
     while(rest < wp_w && delta - rest >= ten_kappa &&
           (rest + ten_kappa < wp_w || 
            wp_w - rest > rest + ten_kappa - wp_w))
     {
         buffer[len - 1]--;
         rest += ten_kappa;
     }
 }
  
 inline int CountDecimalDigit32(uint32_t n)
 {
     // Simple pure C++ implementation was faster than __builtin_clz version in this situation.
     if(n < 10)
         return 1;
     if(n < 100)
         return 2;
     if(n < 1000)
         return 3;
     if(n < 10000)
         return 4;
     if(n < 100000)
         return 5;
     if(n < 1000000)
         return 6;
     if(n < 10000000)
         return 7;
     if(n < 100000000)
         return 8;
     // Will not reach 10 digits in DigitGen()
     // if (n < 1000000000) return 9;
     // return 10;
     return 9;
 }
  
 inline void
 DigitGen(const DiyFp& W, const DiyFp& Mp, uint64_t delta, char* buffer, int* len, int* K)
 {
     static const uint64_t kPow10[] = {1ULL,
                                       10ULL,
                                       100ULL,
                                       1000ULL,
                                       10000ULL,
                                       100000ULL,
                                       1000000ULL,
                                       10000000ULL,
                                       100000000ULL,
                                       1000000000ULL,
                                       10000000000ULL,
                                       100000000000ULL,
                                       1000000000000ULL,
                                       10000000000000ULL,
                                       100000000000000ULL,
                                       1000000000000000ULL,
                                       10000000000000000ULL,
                                       100000000000000000ULL,
                                       1000000000000000000ULL,
                                       10000000000000000000ULL};
     const DiyFp one(uint64_t(1) << -Mp.e, Mp.e);
     const DiyFp wp_w = Mp - W;
     uint32_t p1      = static_cast<uint32_t>(Mp.f >> -one.e);
     uint64_t p2      = Mp.f & (one.f - 1);
     int kappa        = CountDecimalDigit32(p1); // kappa in [0, 9]
     *len             = 0;
  
     while(kappa > 0)
     {
         uint32_t d = 0;
         switch(kappa)
         {
         case 9:
             d = p1 / 100000000;
             p1 %= 100000000;
             break;
         case 8:
             d = p1 / 10000000;
             p1 %= 10000000;
             break;
         case 7:
             d = p1 / 1000000;
             p1 %= 1000000;
             break;
         case 6:
             d = p1 / 100000;
             p1 %= 100000;
             break;
         case 5:
             d = p1 / 10000;
             p1 %= 10000;
             break;
         case 4:
             d = p1 / 1000;
             p1 %= 1000;
             break;
         case 3:
             d = p1 / 100;
             p1 %= 100;
             break;
         case 2:
             d = p1 / 10;
             p1 %= 10;
             break;
         case 1:
             d  = p1;
             p1 = 0;
             break;
         default:;
         }
         if(d || *len)
             buffer[(*len)++] = static_cast<char>('0' + static_cast<char>(d));
         kappa--;
         uint64_t tmp = (static_cast<uint64_t>(p1) << -one.e) + p2;
         if(tmp <= delta)
         {
             *K += kappa;
             GrisuRound(buffer, *len, delta, tmp, kPow10[kappa] << -one.e, wp_w.f);
             return;
         }
     }
  
     // kappa = 0
     for(;;)
     {
         p2 *= 10;
         delta *= 10;
         char d = static_cast<char>(p2 >> -one.e);
         if(d || *len)
             buffer[(*len)++] = static_cast<char>('0' + d);
         p2 &= one.f - 1;
         kappa--;
         if(p2 < delta)
         {
             *K += kappa;
             int index = -kappa;
             GrisuRound(buffer, *len, delta, p2, one.f, wp_w.f * (index < 20 ? kPow10[index] : 0));
             return;
         }
     }
 }
  
 inline void Grisu2(double value, char* buffer, int* length, int* K)
 {
     const DiyFp v(value);
     DiyFp w_m, w_p;
     v.NormalizedBoundaries(&w_m, &w_p);
  
     const DiyFp c_mk = GetCachedPower(w_p.e, K);
     const DiyFp W    = v.Normalize() * c_mk;
     DiyFp Wp         = w_p * c_mk;
     DiyFp Wm         = w_m * c_mk;
     Wm.f++;
     Wp.f--;
     DigitGen(W, Wp, Wp.f - Wm.f, buffer, length, K);
 }
  
 inline char* WriteExponent(int K, char* buffer)
 {
     if(K < 0)
     {
         *buffer++ = '-';
         K         = -K;
     }
  
     if(K >= 100)
     {
         *buffer++ = static_cast<char>('0' + static_cast<char>(K / 100));
         K %= 100;
         const char* d = GetDigitsLut() + K * 2;
         *buffer++     = d[0];
         *buffer++     = d[1];
     }
     else if(K >= 10)
     {
         const char* d = GetDigitsLut() + K * 2;
         *buffer++     = d[0];
         *buffer++     = d[1];
     }
     else
         *buffer++ = static_cast<char>('0' + static_cast<char>(K));
  
     return buffer;
 }
  
 inline char* Prettify(char* buffer, int length, int k, int maxDecimalPlaces)
 {
     const int kk = length + k; // 10^(kk-1) <= v < 10^kk
  
     if(0 <= k && kk <= 21)
     {
         // 1234e7 -> 12340000000
         for(int i = length; i < kk; i++)
             buffer[i] = '0';
         buffer[kk]     = '.';
         buffer[kk + 1] = '0';
         return &buffer[kk + 2];
     }
     else if(0 < kk && kk <= 21)
     {
         // 1234e-2 -> 12.34
         std::memmove(&buffer[kk + 1], &buffer[kk], static_cast<size_t>(length - kk));
         buffer[kk] = '.';
         if(0 > k + maxDecimalPlaces)
         {
             // When maxDecimalPlaces = 2, 1.2345 -> 1.23, 1.102 -> 1.1
             // Remove extra trailing zeros (at least one) after truncation.
             for(int i = kk + maxDecimalPlaces; i > kk + 1; i--)
                 if(buffer[i] != '0')
                     return &buffer[i + 1];
             return &buffer[kk + 2]; // Reserve one zero
         }
         else
             return &buffer[length + 1];
     }
     else if(-6 < kk && kk <= 0)
     {
         // 1234e-6 -> 0.001234
         const int offset = 2 - kk;
         std::memmove(&buffer[offset], &buffer[0], static_cast<size_t>(length));
         buffer[0] = '0';
         buffer[1] = '.';
         for(int i = 2; i < offset; i++)
             buffer[i] = '0';
         if(length - kk > maxDecimalPlaces)
         {
             // When maxDecimalPlaces = 2, 0.123 -> 0.12, 0.102 -> 0.1
             // Remove extra trailing zeros (at least one) after truncation.
             for(int i = maxDecimalPlaces + 1; i > 2; i--)
                 if(buffer[i] != '0')
                     return &buffer[i + 1];
             return &buffer[3]; // Reserve one zero
         }
         else
             return &buffer[length + offset];
     }
     else if(kk < -maxDecimalPlaces)
     {
         // Truncate to zero
         buffer[0] = '0';
         buffer[1] = '.';
         buffer[2] = '0';
         return &buffer[3];
     }
     else if(length == 1)
     {
         // 1e30
         buffer[1] = 'e';
         return WriteExponent(kk - 1, &buffer[2]);
     }
     else
     {
         // 1234e30 -> 1.234e33
         std::memmove(&buffer[2], &buffer[1], static_cast<size_t>(length - 1));
         buffer[1]          = '.';
         buffer[length + 1] = 'e';
         return WriteExponent(kk - 1, &buffer[0 + length + 2]);
     }
 }
  
 inline char* dtoa(double value, char* buffer, int maxDecimalPlaces = 324)
 {
     RAPIDJSON_ASSERT(maxDecimalPlaces >= 1);
     Double d(value);
     if(d.IsZero())
     {
         if(d.Sign())
             *buffer++ = '-'; // -0.0, Issue #289
         buffer[0] = '0';
         buffer[1] = '.';
         buffer[2] = '0';
         return &buffer[3];
     }
     else
     {
         if(value < 0)
         {
             *buffer++ = '-';
             value     = -value;
         }
         int length, K;
         Grisu2(value, buffer, &length, &K);
         return Prettify(buffer, length, K, maxDecimalPlaces);
     }
 }
  
 #ifdef __GNUC__
 RAPIDJSON_DIAG_POP
 #endif
  
 } // namespace internal
 RAPIDJSON_NAMESPACE_END
  
 #endif // RAPIDJSON_DTOA_