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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. All rights reserved.
+//
+// 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 || /// closer
+ wp_w - rest > rest + ten_kappa - wp_w)) {
+ buffer[len - 1]--;
+ rest += ten_kappa;
+ }
+}
+
+inline unsigned 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 uint32_t kPow10[] = { 1, 10, 100, 1000, 10000, 100000, 1000000, 10000000, 100000000, 1000000000 };
+ 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);
+ unsigned 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, static_cast<uint64_t>(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 = -static_cast<int>(kappa);
+ GrisuRound(buffer, *len, delta, p2, one.f, wp_w.f * (index < 9 ? kPow10[-static_cast<int>(kappa)] : 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_
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