ceph/src/rapidjson/include/rapidjson/internal/dtoa.h

   1 // Tencent is pleased to support the open source community by making RapidJSON available.
   2 //
   3 // Copyright (C) 2015 THL A29 Limited, a Tencent company, and Milo Yip. All rights reserved.
   4 //
   5 // Licensed under the MIT License (the "License"); you may not use this file except
   6 // in compliance with the License. You may obtain a copy of the License at
   7 //
   8 // http://opensource.org/licenses/MIT
   9 //
  10 // Unless required by applicable law or agreed to in writing, software distributed
  11 // under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR
  12 // CONDITIONS OF ANY KIND, either express or implied. See the License for the
  13 // specific language governing permissions and limitations under the License.
  14
  15 // This is a C++ header-only implementation of Grisu2 algorithm from the publication:
  16 // Loitsch, Florian. "Printing floating-point numbers quickly and accurately with
  17 // integers." ACM Sigplan Notices 45.6 (2010): 233-243.
  18
  19 #ifndef RAPIDJSON_DTOA_
  20 #define RAPIDJSON_DTOA_
  21
  22 #include "itoa.h" // GetDigitsLut()
  23 #include "diyfp.h"
  24 #include "ieee754.h"
  25
  26 RAPIDJSON_NAMESPACE_BEGIN
  27 namespace internal {
  28
  29 #ifdef __GNUC__
  30 RAPIDJSON_DIAG_PUSH
  31 RAPIDJSON_DIAG_OFF(effc++)
  32 RAPIDJSON_DIAG_OFF(array-bounds) // some gcc versions generate wrong warnings https://gcc.gnu.org/bugzilla/show_bug.cgi?id=59124
  33 #endif
  34
  35 inline void GrisuRound(char* buffer, int len, uint64_t delta, uint64_t rest, uint64_t ten_kappa, uint64_t wp_w) {
  36     while (rest < wp_w && delta - rest >= ten_kappa &&
  37            (rest + ten_kappa < wp_w ||  /// closer
  38             wp_w - rest > rest + ten_kappa - wp_w)) {
  39         buffer[len - 1]--;
  40         rest += ten_kappa;
  41     }
  42 }
  43
  44 inline unsigned CountDecimalDigit32(uint32_t n) {
  45     // Simple pure C++ implementation was faster than __builtin_clz version in this situation.
  46     if (n < 10) return 1;
  47     if (n < 100) return 2;
  48     if (n < 1000) return 3;
  49     if (n < 10000) return 4;
  50     if (n < 100000) return 5;
  51     if (n < 1000000) return 6;
  52     if (n < 10000000) return 7;
  53     if (n < 100000000) return 8;
  54     // Will not reach 10 digits in DigitGen()
  55     //if (n < 1000000000) return 9;
  56     //return 10;
  57     return 9;
  58 }
  59
  60 inline void DigitGen(const DiyFp& W, const DiyFp& Mp, uint64_t delta, char* buffer, int* len, int* K) {
  61     static const uint32_t kPow10[] = { 1, 10, 100, 1000, 10000, 100000, 1000000, 10000000, 100000000, 1000000000 };
  62     const DiyFp one(uint64_t(1) << -Mp.e, Mp.e);
  63     const DiyFp wp_w = Mp - W;
  64     uint32_t p1 = static_cast<uint32_t>(Mp.f >> -one.e);
  65     uint64_t p2 = Mp.f & (one.f - 1);
  66     unsigned kappa = CountDecimalDigit32(p1); // kappa in [0, 9]
  67     *len = 0;
  68
  69     while (kappa > 0) {
  70         uint32_t d = 0;
  71         switch (kappa) {
  72             case  9: d = p1 /  100000000; p1 %=  100000000; break;
  73             case  8: d = p1 /   10000000; p1 %=   10000000; break;
  74             case  7: d = p1 /    1000000; p1 %=    1000000; break;
  75             case  6: d = p1 /     100000; p1 %=     100000; break;
  76             case  5: d = p1 /      10000; p1 %=      10000; break;
  77             case  4: d = p1 /       1000; p1 %=       1000; break;
  78             case  3: d = p1 /        100; p1 %=        100; break;
  79             case  2: d = p1 /         10; p1 %=         10; break;
  80             case  1: d = p1;              p1 =           0; break;
  81             default:;
  82         }
  83         if (d || *len)
  84             buffer[(*len)++] = static_cast<char>('0' + static_cast<char>(d));
  85         kappa--;
  86         uint64_t tmp = (static_cast<uint64_t>(p1) << -one.e) + p2;
  87         if (tmp <= delta) {
  88             *K += kappa;
  89             GrisuRound(buffer, *len, delta, tmp, static_cast<uint64_t>(kPow10[kappa]) << -one.e, wp_w.f);
  90             return;
  91         }
  92     }
  93
  94     // kappa = 0
  95     for (;;) {
  96         p2 *= 10;
  97         delta *= 10;
  98         char d = static_cast<char>(p2 >> -one.e);
  99         if (d || *len)
 100             buffer[(*len)++] = static_cast<char>('0' + d);
 101         p2 &= one.f - 1;
 102         kappa--;
 103         if (p2 < delta) {
 104             *K += kappa;
 105             int index = -static_cast<int>(kappa);
 106             GrisuRound(buffer, *len, delta, p2, one.f, wp_w.f * (index < 9 ? kPow10[-static_cast<int>(kappa)] : 0));
 107             return;
 108         }
 109     }
 110 }
 111
 112 inline void Grisu2(double value, char* buffer, int* length, int* K) {
 113     const DiyFp v(value);
 114     DiyFp w_m, w_p;
 115     v.NormalizedBoundaries(&w_m, &w_p);
 116
 117     const DiyFp c_mk = GetCachedPower(w_p.e, K);
 118     const DiyFp W = v.Normalize() * c_mk;
 119     DiyFp Wp = w_p * c_mk;
 120     DiyFp Wm = w_m * c_mk;
 121     Wm.f++;
 122     Wp.f--;
 123     DigitGen(W, Wp, Wp.f - Wm.f, buffer, length, K);
 124 }
 125
 126 inline char* WriteExponent(int K, char* buffer) {
 127     if (K < 0) {
 128         *buffer++ = '-';
 129         K = -K;
 130     }
 131
 132     if (K >= 100) {
 133         *buffer++ = static_cast<char>('0' + static_cast<char>(K / 100));
 134         K %= 100;
 135         const char* d = GetDigitsLut() + K * 2;
 136         *buffer++ = d[0];
 137         *buffer++ = d[1];
 138     }
 139     else if (K >= 10) {
 140         const char* d = GetDigitsLut() + K * 2;
 141         *buffer++ = d[0];
 142         *buffer++ = d[1];
 143     }
 144     else
 145         *buffer++ = static_cast<char>('0' + static_cast<char>(K));
 146
 147     return buffer;
 148 }
 149
 150 inline char* Prettify(char* buffer, int length, int k, int maxDecimalPlaces) {
 151     const int kk = length + k;  // 10^(kk-1) <= v < 10^kk
 152
 153     if (0 <= k && kk <= 21) {
 154         // 1234e7 -> 12340000000
 155         for (int i = length; i < kk; i++)
 156             buffer[i] = '0';
 157         buffer[kk] = '.';
 158         buffer[kk + 1] = '0';
 159         return &buffer[kk + 2];
 160     }
 161     else if (0 < kk && kk <= 21) {
 162         // 1234e-2 -> 12.34
 163         std::memmove(&buffer[kk + 1], &buffer[kk], static_cast<size_t>(length - kk));
 164         buffer[kk] = '.';
 165         if (0 > k + maxDecimalPlaces) {
 166             // When maxDecimalPlaces = 2, 1.2345 -> 1.23, 1.102 -> 1.1
 167             // Remove extra trailing zeros (at least one) after truncation.
 168             for (int i = kk + maxDecimalPlaces; i > kk + 1; i--)
 169                 if (buffer[i] != '0')
 170                     return &buffer[i + 1];
 171             return &buffer[kk + 2]; // Reserve one zero
 172         }
 173         else
 174             return &buffer[length + 1];
 175     }
 176     else if (-6 < kk && kk <= 0) {
 177         // 1234e-6 -> 0.001234
 178         const int offset = 2 - kk;
 179         std::memmove(&buffer[offset], &buffer[0], static_cast<size_t>(length));
 180         buffer[0] = '0';
 181         buffer[1] = '.';
 182         for (int i = 2; i < offset; i++)
 183             buffer[i] = '0';
 184         if (length - kk > maxDecimalPlaces) {
 185             // When maxDecimalPlaces = 2, 0.123 -> 0.12, 0.102 -> 0.1
 186             // Remove extra trailing zeros (at least one) after truncation.
 187             for (int i = maxDecimalPlaces + 1; i > 2; i--)
 188                 if (buffer[i] != '0')
 189                     return &buffer[i + 1];
 190             return &buffer[3]; // Reserve one zero
 191         }
 192         else
 193             return &buffer[length + offset];
 194     }
 195     else if (kk < -maxDecimalPlaces) {
 196         // Truncate to zero
 197         buffer[0] = '0';
 198         buffer[1] = '.';
 199         buffer[2] = '0';
 200         return &buffer[3];
 201     }
 202     else if (length == 1) {
 203         // 1e30
 204         buffer[1] = 'e';
 205         return WriteExponent(kk - 1, &buffer[2]);
 206     }
 207     else {
 208         // 1234e30 -> 1.234e33
 209         std::memmove(&buffer[2], &buffer[1], static_cast<size_t>(length - 1));
 210         buffer[1] = '.';
 211         buffer[length + 1] = 'e';
 212         return WriteExponent(kk - 1, &buffer[0 + length + 2]);
 213     }
 214 }
 215
 216 inline char* dtoa(double value, char* buffer, int maxDecimalPlaces = 324) {
 217     RAPIDJSON_ASSERT(maxDecimalPlaces >= 1);
 218     Double d(value);
 219     if (d.IsZero()) {
 220         if (d.Sign())
 221             *buffer++ = '-';     // -0.0, Issue #289
 222         buffer[0] = '0';
 223         buffer[1] = '.';
 224         buffer[2] = '0';
 225         return &buffer[3];
 226     }
 227     else {
 228         if (value < 0) {
 229             *buffer++ = '-';
 230             value = -value;
 231         }
 232         int length, K;
 233         Grisu2(value, buffer, &length, &K);
 234         return Prettify(buffer, length, K, maxDecimalPlaces);
 235     }
 236 }
 237
 238 #ifdef __GNUC__
 239 RAPIDJSON_DIAG_POP
 240 #endif
 241
 242 } // namespace internal
 243 RAPIDJSON_NAMESPACE_END
 244
 245 #endif // RAPIDJSON_DTOA_