blame: source/code/Libs/include/cereal/external/rapidjson/internal/dtoa.h

// 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 CEREAL_RAPIDJSON_DTOA_

#define CEREAL_RAPIDJSON_DTOA_

#include "itoa.h" // GetDigitsLut()

#include "diyfp.h"

#include "ieee754.h"

CEREAL_RAPIDJSON_NAMESPACE_BEGIN

namespace internal {

#ifdef __GNUC__

CEREAL_RAPIDJSON_DIAG_PUSH

CEREAL_RAPIDJSON_DIAG_OFF(effc++)

CEREAL_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) {

    CEREAL_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__

CEREAL_RAPIDJSON_DIAG_POP

#endif

} // namespace internal

CEREAL_RAPIDJSON_NAMESPACE_END

#endif // CEREAL_RAPIDJSON_DTOA_