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Diffstat (limited to 'include/rapidjson/internal/dtoa.h')
| -rw-r--r-- | include/rapidjson/internal/dtoa.h | 245 |
1 files changed, 245 insertions, 0 deletions
diff --git a/include/rapidjson/internal/dtoa.h b/include/rapidjson/internal/dtoa.h new file mode 100644 index 0000000..bf2e9b2 --- /dev/null +++ b/include/rapidjson/internal/dtoa.h @@ -0,0 +1,245 @@ +// 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 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 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); + 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, 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 = -kappa; + GrisuRound(buffer, *len, delta, p2, one.f, wp_w.f * (index < 9 ? 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_ |