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