writer.h

// -*- tab-width: 2; indent-tabs-mode: nil; coding: utf-8-with-signature -*-
// 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.
//
// 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.
 
#ifndef RAPIDJSON_WRITER_H_
#define RAPIDJSON_WRITER_H_
 
#include "stream.h"
#include "internal/clzll.h"
#include "internal/meta.h"
#include "internal/stack.h"
#include "internal/strfunc.h"
#include "internal/dtoa.h"
#include "internal/itoa.h"
#include "stringbuffer.h"
#include <new>      // placement new
 
#if defined(RAPIDJSON_SIMD) && defined(_MSC_VER)
#include <intrin.h>
#pragma intrinsic(_BitScanForward)
#endif
#ifdef RAPIDJSON_SSE42
#include <nmmintrin.h>
#elif defined(RAPIDJSON_SSE2)
#include <emmintrin.h>
#elif defined(RAPIDJSON_NEON)
#include <arm_neon.h>
#endif
 
#ifdef __clang__
RAPIDJSON_DIAG_PUSH
RAPIDJSON_DIAG_OFF(padded)
RAPIDJSON_DIAG_OFF(unreachable-code)
RAPIDJSON_DIAG_OFF(c++98-compat)
#elif defined(_MSC_VER)
RAPIDJSON_DIAG_PUSH
RAPIDJSON_DIAG_OFF(4127) // conditional expression is constant
#endif
 
RAPIDJSON_NAMESPACE_BEGIN

// WriteFlag

#ifndef RAPIDJSON_WRITE_DEFAULT_FLAGS
#define RAPIDJSON_WRITE_DEFAULT_FLAGS kWriteNoFlags
#endif

enum WriteFlag {
    kWriteNoFlags = 0,              
    kWriteValidateEncodingFlag = 1, 
    kWriteNanAndInfFlag = 2,        
    kWriteNanAndInfNullFlag = 4,    
    kWriteDefaultFlags = RAPIDJSON_WRITE_DEFAULT_FLAGS  
};


template<typename OutputStream, typename SourceEncoding = UTF8<>, typename TargetEncoding = UTF8<>, typename StackAllocator = CrtAllocator, unsigned writeFlags = kWriteDefaultFlags>
class Writer {
public:
    typedef typename SourceEncoding::Ch Ch;
 
    static const int kDefaultMaxDecimalPlaces = 324;


    explicit
    Writer(OutputStream& os, StackAllocator* stackAllocator = 0, size_t levelDepth = kDefaultLevelDepth) : 
        os_(&os), level_stack_(stackAllocator, levelDepth * sizeof(Level)), maxDecimalPlaces_(kDefaultMaxDecimalPlaces), hasRoot_(false) {}
 
    explicit
    Writer(StackAllocator* allocator = 0, size_t levelDepth = kDefaultLevelDepth) :
        os_(0), level_stack_(allocator, levelDepth * sizeof(Level)), maxDecimalPlaces_(kDefaultMaxDecimalPlaces), hasRoot_(false) {}
 
#if RAPIDJSON_HAS_CXX11_RVALUE_REFS
    Writer(Writer&& rhs) :
        os_(rhs.os_), level_stack_(std::move(rhs.level_stack_)), maxDecimalPlaces_(rhs.maxDecimalPlaces_), hasRoot_(rhs.hasRoot_) {
        rhs.os_ = 0;
    }
#endif


    void Reset(OutputStream& os) {
        os_ = &os;
        hasRoot_ = false;
        level_stack_.Clear();
    }


    bool IsComplete() const {
        return hasRoot_ && level_stack_.Empty();
    }
 
    int GetMaxDecimalPlaces() const {
        return maxDecimalPlaces_;
    }


    void SetMaxDecimalPlaces(int maxDecimalPlaces) {
        maxDecimalPlaces_ = maxDecimalPlaces;
    }

 
    bool Null()                 { Prefix(kNullType);   return EndValue(WriteNull()); }
    bool Bool(bool b)           { Prefix(b ? kTrueType : kFalseType); return EndValue(WriteBool(b)); }
    bool Int(int i)             { Prefix(kNumberType); return EndValue(WriteInt(i)); }
    bool Uint(unsigned u)       { Prefix(kNumberType); return EndValue(WriteUint(u)); }
    bool Int64(int64_t i64)     { Prefix(kNumberType); return EndValue(WriteInt64(i64)); }
    bool Uint64(uint64_t u64)   { Prefix(kNumberType); return EndValue(WriteUint64(u64)); }


    bool Double(double d)       { Prefix(kNumberType); return EndValue(WriteDouble(d)); }
 
    bool RawNumber(const Ch* str, SizeType length, bool copy = false) {
        RAPIDJSON_ASSERT(str != 0);
        (void)copy;
        Prefix(kNumberType);
        return EndValue(WriteString(str, length));
    }
 
    bool String(const Ch* str, SizeType length, bool copy = false) {
        RAPIDJSON_ASSERT(str != 0);
        (void)copy;
        Prefix(kStringType);
        return EndValue(WriteString(str, length));
    }
 
#if RAPIDJSON_HAS_STDSTRING
    bool String(const std::basic_string<Ch>& str) {
        return String(str.data(), SizeType(str.size()));
    }
#endif
 
    bool StartObject() {
        Prefix(kObjectType);
        new (level_stack_.template Push<Level>()) Level(false);
        return WriteStartObject();
    }
 
    bool Key(const Ch* str, SizeType length, bool copy = false) { return String(str, length, copy); }
 
#if RAPIDJSON_HAS_STDSTRING
    bool Key(const std::basic_string<Ch>& str)
    {
      return Key(str.data(), SizeType(str.size()));
    }
#endif
 
    bool EndObject(SizeType memberCount = 0) {
        (void)memberCount;
        RAPIDJSON_ASSERT(level_stack_.GetSize() >= sizeof(Level)); // not inside an Object
        RAPIDJSON_ASSERT(!level_stack_.template Top<Level>()->inArray); // currently inside an Array, not Object
        RAPIDJSON_ASSERT(0 == level_stack_.template Top<Level>()->valueCount % 2); // Object has a Key without a Value
        level_stack_.template Pop<Level>(1);
        return EndValue(WriteEndObject());
    }
 
    bool StartArray() {
        Prefix(kArrayType);
        new (level_stack_.template Push<Level>()) Level(true);
        return WriteStartArray();
    }
 
    bool EndArray(SizeType elementCount = 0) {
        (void)elementCount;
        RAPIDJSON_ASSERT(level_stack_.GetSize() >= sizeof(Level));
        RAPIDJSON_ASSERT(level_stack_.template Top<Level>()->inArray);
        level_stack_.template Pop<Level>(1);
        return EndValue(WriteEndArray());
    }


    bool String(const Ch* const& str) { return String(str, internal::StrLen(str)); }
    bool Key(const Ch* const& str) { return Key(str, internal::StrLen(str)); }
    


    bool RawValue(const Ch* json, size_t length, Type type) {
        RAPIDJSON_ASSERT(json != 0);
        Prefix(type);
        return EndValue(WriteRawValue(json, length));
    }


    void Flush() {
        os_->Flush();
    }
 
    static const size_t kDefaultLevelDepth = 32;
 
protected:
    struct Level {
        Level(bool inArray_) : valueCount(0), inArray(inArray_) {}
        size_t valueCount;  
        bool inArray;       
    };
 
    bool WriteNull()  {
        PutReserve(*os_, 4);
        PutUnsafe(*os_, 'n'); PutUnsafe(*os_, 'u'); PutUnsafe(*os_, 'l'); PutUnsafe(*os_, 'l'); return true;
    }
 
    bool WriteBool(bool b)  {
        if (b) {
            PutReserve(*os_, 4);
            PutUnsafe(*os_, 't'); PutUnsafe(*os_, 'r'); PutUnsafe(*os_, 'u'); PutUnsafe(*os_, 'e');
        }
        else {
            PutReserve(*os_, 5);
            PutUnsafe(*os_, 'f'); PutUnsafe(*os_, 'a'); PutUnsafe(*os_, 'l'); PutUnsafe(*os_, 's'); PutUnsafe(*os_, 'e');
        }
        return true;
    }
 
    bool WriteInt(int i) {
        char buffer[11];
        const char* end = internal::i32toa(i, buffer);
        PutReserve(*os_, static_cast<size_t>(end - buffer));
        for (const char* p = buffer; p != end; ++p)
            PutUnsafe(*os_, static_cast<typename OutputStream::Ch>(*p));
        return true;
    }
 
    bool WriteUint(unsigned u) {
        char buffer[10];
        const char* end = internal::u32toa(u, buffer);
        PutReserve(*os_, static_cast<size_t>(end - buffer));
        for (const char* p = buffer; p != end; ++p)
            PutUnsafe(*os_, static_cast<typename OutputStream::Ch>(*p));
        return true;
    }
 
    bool WriteInt64(int64_t i64) {
        char buffer[21];
        const char* end = internal::i64toa(i64, buffer);
        PutReserve(*os_, static_cast<size_t>(end - buffer));
        for (const char* p = buffer; p != end; ++p)
            PutUnsafe(*os_, static_cast<typename OutputStream::Ch>(*p));
        return true;
    }
 
    bool WriteUint64(uint64_t u64) {
        char buffer[20];
        char* end = internal::u64toa(u64, buffer);
        PutReserve(*os_, static_cast<size_t>(end - buffer));
        for (char* p = buffer; p != end; ++p)
            PutUnsafe(*os_, static_cast<typename OutputStream::Ch>(*p));
        return true;
    }
 
    bool WriteDouble(double d) {
        if (internal::Double(d).IsNanOrInf()) {
            if (!(writeFlags & kWriteNanAndInfFlag) && !(writeFlags & kWriteNanAndInfNullFlag))
                return false;
            if (writeFlags & kWriteNanAndInfNullFlag) {
                PutReserve(*os_, 4);
                PutUnsafe(*os_, 'n'); PutUnsafe(*os_, 'u'); PutUnsafe(*os_, 'l'); PutUnsafe(*os_, 'l');
                return true;
            }
            if (internal::Double(d).IsNan()) {
                PutReserve(*os_, 3);
                PutUnsafe(*os_, 'N'); PutUnsafe(*os_, 'a'); PutUnsafe(*os_, 'N');
                return true;
            }
            if (internal::Double(d).Sign()) {
                PutReserve(*os_, 9);
                PutUnsafe(*os_, '-');
            }
            else
                PutReserve(*os_, 8);
            PutUnsafe(*os_, 'I'); PutUnsafe(*os_, 'n'); PutUnsafe(*os_, 'f');
            PutUnsafe(*os_, 'i'); PutUnsafe(*os_, 'n'); PutUnsafe(*os_, 'i'); PutUnsafe(*os_, 't'); PutUnsafe(*os_, 'y');
            return true;
        }
 
        char buffer[25];
        char* end = internal::dtoa(d, buffer, maxDecimalPlaces_);
        PutReserve(*os_, static_cast<size_t>(end - buffer));
        for (char* p = buffer; p != end; ++p)
            PutUnsafe(*os_, static_cast<typename OutputStream::Ch>(*p));
        return true;
    }
 
    bool WriteString(const Ch* str, SizeType length)  {
        static const typename OutputStream::Ch hexDigits[16] = { '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'A', 'B', 'C', 'D', 'E', 'F' };
        static const char escape[256] = {
#define Z16 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0
            //0    1    2    3    4    5    6    7    8    9    A    B    C    D    E    F
            'u', 'u', 'u', 'u', 'u', 'u', 'u', 'u', 'b', 't', 'n', 'u', 'f', 'r', 'u', 'u', // 00
            'u', 'u', 'u', 'u', 'u', 'u', 'u', 'u', 'u', 'u', 'u', 'u', 'u', 'u', 'u', 'u', // 10
              0,   0, '"',   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0, // 20
            Z16, Z16,                                                                       // 30~4F
              0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,'\\',   0,   0,   0, // 50
            Z16, Z16, Z16, Z16, Z16, Z16, Z16, Z16, Z16, Z16                                // 60~FF
#undef Z16
        };
 
        if (TargetEncoding::supportUnicode)
            PutReserve(*os_, 2 + length * 6); // "\uxxxx..."
        else
            PutReserve(*os_, 2 + length * 12);  // "\uxxxx\uyyyy..."
 
        PutUnsafe(*os_, '\"');
        GenericStringStream<SourceEncoding> is(str);
        while (ScanWriteUnescapedString(is, length)) {
            const Ch c = is.Peek();
            if (!TargetEncoding::supportUnicode && static_cast<unsigned>(c) >= 0x80) {
                // Unicode escaping
                unsigned codepoint;
                if (RAPIDJSON_UNLIKELY(!SourceEncoding::Decode(is, &codepoint)))
                    return false;
                PutUnsafe(*os_, '\\');
                PutUnsafe(*os_, 'u');
                if (codepoint <= 0xD7FF || (codepoint >= 0xE000 && codepoint <= 0xFFFF)) {
                    PutUnsafe(*os_, hexDigits[(codepoint >> 12) & 15]);
                    PutUnsafe(*os_, hexDigits[(codepoint >>  8) & 15]);
                    PutUnsafe(*os_, hexDigits[(codepoint >>  4) & 15]);
                    PutUnsafe(*os_, hexDigits[(codepoint      ) & 15]);
                }
                else {
                    RAPIDJSON_ASSERT(codepoint >= 0x010000 && codepoint <= 0x10FFFF);
                    // Surrogate pair
                    unsigned s = codepoint - 0x010000;
                    unsigned lead = (s >> 10) + 0xD800;
                    unsigned trail = (s & 0x3FF) + 0xDC00;
                    PutUnsafe(*os_, hexDigits[(lead >> 12) & 15]);
                    PutUnsafe(*os_, hexDigits[(lead >>  8) & 15]);
                    PutUnsafe(*os_, hexDigits[(lead >>  4) & 15]);
                    PutUnsafe(*os_, hexDigits[(lead      ) & 15]);
                    PutUnsafe(*os_, '\\');
                    PutUnsafe(*os_, 'u');
                    PutUnsafe(*os_, hexDigits[(trail >> 12) & 15]);
                    PutUnsafe(*os_, hexDigits[(trail >>  8) & 15]);
                    PutUnsafe(*os_, hexDigits[(trail >>  4) & 15]);
                    PutUnsafe(*os_, hexDigits[(trail      ) & 15]);                    
                }
            }
            else if ((sizeof(Ch) == 1 || static_cast<unsigned>(c) < 256) && RAPIDJSON_UNLIKELY(escape[static_cast<unsigned char>(c)]))  {
                is.Take();
                PutUnsafe(*os_, '\\');
                PutUnsafe(*os_, static_cast<typename OutputStream::Ch>(escape[static_cast<unsigned char>(c)]));
                if (escape[static_cast<unsigned char>(c)] == 'u') {
                    PutUnsafe(*os_, '0');
                    PutUnsafe(*os_, '0');
                    PutUnsafe(*os_, hexDigits[static_cast<unsigned char>(c) >> 4]);
                    PutUnsafe(*os_, hexDigits[static_cast<unsigned char>(c) & 0xF]);
                }
            }
            else if (RAPIDJSON_UNLIKELY(!(writeFlags & kWriteValidateEncodingFlag ? 
                Transcoder<SourceEncoding, TargetEncoding>::Validate(is, *os_) :
                Transcoder<SourceEncoding, TargetEncoding>::TranscodeUnsafe(is, *os_))))
                return false;
        }
        PutUnsafe(*os_, '\"');
        return true;
    }
 
    bool ScanWriteUnescapedString(GenericStringStream<SourceEncoding>& is, size_t length) {
        return RAPIDJSON_LIKELY(is.Tell() < length);
    }
 
    bool WriteStartObject() { os_->Put('{'); return true; }
    bool WriteEndObject()   { os_->Put('}'); return true; }
    bool WriteStartArray()  { os_->Put('['); return true; }
    bool WriteEndArray()    { os_->Put(']'); return true; }
 
    bool WriteRawValue(const Ch* json, size_t length) {
        PutReserve(*os_, length);
        GenericStringStream<SourceEncoding> is(json);
        while (RAPIDJSON_LIKELY(is.Tell() < length)) {
            RAPIDJSON_ASSERT(is.Peek() != '\0');
            if (RAPIDJSON_UNLIKELY(!(writeFlags & kWriteValidateEncodingFlag ? 
                Transcoder<SourceEncoding, TargetEncoding>::Validate(is, *os_) :
                Transcoder<SourceEncoding, TargetEncoding>::TranscodeUnsafe(is, *os_))))
                return false;
        }
        return true;
    }
 
    void Prefix(Type type) {
        (void)type;
        if (RAPIDJSON_LIKELY(level_stack_.GetSize() != 0)) { // this value is not at root
            Level* level = level_stack_.template Top<Level>();
            if (level->valueCount > 0) {
                if (level->inArray) 
                    os_->Put(','); // add comma if it is not the first element in array
                else  // in object
                    os_->Put((level->valueCount % 2 == 0) ? ',' : ':');
            }
            if (!level->inArray && level->valueCount % 2 == 0)
                RAPIDJSON_ASSERT(type == kStringType);  // if it's in object, then even number should be a name
            level->valueCount++;
        }
        else {
            RAPIDJSON_ASSERT(!hasRoot_);    // Should only has one and only one root.
            hasRoot_ = true;
        }
    }
 
    // Flush the value if it is the top level one.
    bool EndValue(bool ret) {
        if (RAPIDJSON_UNLIKELY(level_stack_.Empty()))   // end of json text
            Flush();
        return ret;
    }
 
    OutputStream* os_;
    internal::Stack<StackAllocator> level_stack_;
    int maxDecimalPlaces_;
    bool hasRoot_;
 
private:
    // Prohibit copy constructor & assignment operator.
    Writer(const Writer&);
    Writer& operator=(const Writer&);
};
 
// Full specialization for StringStream to prevent memory copying
 
template<>
inline bool Writer<StringBuffer>::WriteInt(int i) {
    char *buffer = os_->Push(11);
    const char* end = internal::i32toa(i, buffer);
    os_->Pop(static_cast<size_t>(11 - (end - buffer)));
    return true;
}
 
template<>
inline bool Writer<StringBuffer>::WriteUint(unsigned u) {
    char *buffer = os_->Push(10);
    const char* end = internal::u32toa(u, buffer);
    os_->Pop(static_cast<size_t>(10 - (end - buffer)));
    return true;
}
 
template<>
inline bool Writer<StringBuffer>::WriteInt64(int64_t i64) {
    char *buffer = os_->Push(21);
    const char* end = internal::i64toa(i64, buffer);
    os_->Pop(static_cast<size_t>(21 - (end - buffer)));
    return true;
}
 
template<>
inline bool Writer<StringBuffer>::WriteUint64(uint64_t u) {
    char *buffer = os_->Push(20);
    const char* end = internal::u64toa(u, buffer);
    os_->Pop(static_cast<size_t>(20 - (end - buffer)));
    return true;
}
 
template<>
inline bool Writer<StringBuffer>::WriteDouble(double d) {
    if (internal::Double(d).IsNanOrInf()) {
        // Note: This code path can only be reached if (RAPIDJSON_WRITE_DEFAULT_FLAGS & kWriteNanAndInfFlag).
        if (!(kWriteDefaultFlags & kWriteNanAndInfFlag))
            return false;
        if (kWriteDefaultFlags & kWriteNanAndInfNullFlag) {
            PutReserve(*os_, 4);
            PutUnsafe(*os_, 'n'); PutUnsafe(*os_, 'u'); PutUnsafe(*os_, 'l'); PutUnsafe(*os_, 'l');
            return true;
        }
        if (internal::Double(d).IsNan()) {
            PutReserve(*os_, 3);
            PutUnsafe(*os_, 'N'); PutUnsafe(*os_, 'a'); PutUnsafe(*os_, 'N');
            return true;
        }
        if (internal::Double(d).Sign()) {
            PutReserve(*os_, 9);
            PutUnsafe(*os_, '-');
        }
        else
            PutReserve(*os_, 8);
        PutUnsafe(*os_, 'I'); PutUnsafe(*os_, 'n'); PutUnsafe(*os_, 'f');
        PutUnsafe(*os_, 'i'); PutUnsafe(*os_, 'n'); PutUnsafe(*os_, 'i'); PutUnsafe(*os_, 't'); PutUnsafe(*os_, 'y');
        return true;
    }
    
    char *buffer = os_->Push(25);
    char* end = internal::dtoa(d, buffer, maxDecimalPlaces_);
    os_->Pop(static_cast<size_t>(25 - (end - buffer)));
    return true;
}
 
#if defined(RAPIDJSON_SSE2) || defined(RAPIDJSON_SSE42)
template<>
inline bool Writer<StringBuffer>::ScanWriteUnescapedString(StringStream& is, size_t length) {
    if (length < 16)
        return RAPIDJSON_LIKELY(is.Tell() < length);
 
    if (!RAPIDJSON_LIKELY(is.Tell() < length))
        return false;
 
    const char* p = is.src_;
    const char* end = is.head_ + length;
    const char* nextAligned = reinterpret_cast<const char*>((reinterpret_cast<size_t>(p) + 15) & static_cast<size_t>(~15));
    const char* endAligned = reinterpret_cast<const char*>(reinterpret_cast<size_t>(end) & static_cast<size_t>(~15));
    if (nextAligned > end)
        return true;
 
    while (p != nextAligned)
        if (*p < 0x20 || *p == '\"' || *p == '\\') {
            is.src_ = p;
            return RAPIDJSON_LIKELY(is.Tell() < length);
        }
        else
            os_->PutUnsafe(*p++);
 
    // The rest of string using SIMD
    static const char dquote[16] = { '\"', '\"', '\"', '\"', '\"', '\"', '\"', '\"', '\"', '\"', '\"', '\"', '\"', '\"', '\"', '\"' };
    static const char bslash[16] = { '\\', '\\', '\\', '\\', '\\', '\\', '\\', '\\', '\\', '\\', '\\', '\\', '\\', '\\', '\\', '\\' };
    static const char space[16]  = { 0x1F, 0x1F, 0x1F, 0x1F, 0x1F, 0x1F, 0x1F, 0x1F, 0x1F, 0x1F, 0x1F, 0x1F, 0x1F, 0x1F, 0x1F, 0x1F };
    const __m128i dq = _mm_loadu_si128(reinterpret_cast<const __m128i *>(&dquote[0]));
    const __m128i bs = _mm_loadu_si128(reinterpret_cast<const __m128i *>(&bslash[0]));
    const __m128i sp = _mm_loadu_si128(reinterpret_cast<const __m128i *>(&space[0]));
 
    for (; p != endAligned; p += 16) {
        const __m128i s = _mm_load_si128(reinterpret_cast<const __m128i *>(p));
        const __m128i t1 = _mm_cmpeq_epi8(s, dq);
        const __m128i t2 = _mm_cmpeq_epi8(s, bs);
        const __m128i t3 = _mm_cmpeq_epi8(_mm_max_epu8(s, sp), sp); // s < 0x20 <=> max(s, 0x1F) == 0x1F
        const __m128i x = _mm_or_si128(_mm_or_si128(t1, t2), t3);
        unsigned short r = static_cast<unsigned short>(_mm_movemask_epi8(x));
        if (RAPIDJSON_UNLIKELY(r != 0)) {   // some of characters is escaped
            SizeType len;
#ifdef _MSC_VER         // Find the index of first escaped
            unsigned long offset;
            _BitScanForward(&offset, r);
            len = offset;
#else
            len = static_cast<SizeType>(__builtin_ffs(r) - 1);
#endif
            char* q = reinterpret_cast<char*>(os_->PushUnsafe(len));
            for (size_t i = 0; i < len; i++)
                q[i] = p[i];
 
            p += len;
            break;
        }
        _mm_storeu_si128(reinterpret_cast<__m128i *>(os_->PushUnsafe(16)), s);
    }
 
    is.src_ = p;
    return RAPIDJSON_LIKELY(is.Tell() < length);
}
#elif defined(RAPIDJSON_NEON)
template<>
inline bool Writer<StringBuffer>::ScanWriteUnescapedString(StringStream& is, size_t length) {
    if (length < 16)
        return RAPIDJSON_LIKELY(is.Tell() < length);
 
    if (!RAPIDJSON_LIKELY(is.Tell() < length))
        return false;
 
    const char* p = is.src_;
    const char* end = is.head_ + length;
    const char* nextAligned = reinterpret_cast<const char*>((reinterpret_cast<size_t>(p) + 15) & static_cast<size_t>(~15));
    const char* endAligned = reinterpret_cast<const char*>(reinterpret_cast<size_t>(end) & static_cast<size_t>(~15));
    if (nextAligned > end)
        return true;
 
    while (p != nextAligned)
        if (*p < 0x20 || *p == '\"' || *p == '\\') {
            is.src_ = p;
            return RAPIDJSON_LIKELY(is.Tell() < length);
        }
        else
            os_->PutUnsafe(*p++);
 
    // The rest of string using SIMD
    const uint8x16_t s0 = vmovq_n_u8('"');
    const uint8x16_t s1 = vmovq_n_u8('\\');
    const uint8x16_t s2 = vmovq_n_u8('\b');
    const uint8x16_t s3 = vmovq_n_u8(32);
 
    for (; p != endAligned; p += 16) {
        const uint8x16_t s = vld1q_u8(reinterpret_cast<const uint8_t *>(p));
        uint8x16_t x = vceqq_u8(s, s0);
        x = vorrq_u8(x, vceqq_u8(s, s1));
        x = vorrq_u8(x, vceqq_u8(s, s2));
        x = vorrq_u8(x, vcltq_u8(s, s3));
 
        x = vrev64q_u8(x);                     // Rev in 64
        uint64_t low = vgetq_lane_u64(vreinterpretq_u64_u8(x), 0);   // extract
        uint64_t high = vgetq_lane_u64(vreinterpretq_u64_u8(x), 1);  // extract
 
        SizeType len = 0;
        bool escaped = false;
        if (low == 0) {
            if (high != 0) {
                uint32_t lz = internal::clzll(high);
                len = 8 + (lz >> 3);
                escaped = true;
            }
        } else {
            uint32_t lz = internal::clzll(low);
            len = lz >> 3;
            escaped = true;
        }
        if (RAPIDJSON_UNLIKELY(escaped)) {   // some of characters is escaped
            char* q = reinterpret_cast<char*>(os_->PushUnsafe(len));
            for (size_t i = 0; i < len; i++)
                q[i] = p[i];
 
            p += len;
            break;
        }
        vst1q_u8(reinterpret_cast<uint8_t *>(os_->PushUnsafe(16)), s);
    }
 
    is.src_ = p;
    return RAPIDJSON_LIKELY(is.Tell() < length);
}
#endif // RAPIDJSON_NEON
 
RAPIDJSON_NAMESPACE_END
 
#if defined(_MSC_VER) || defined(__clang__)
RAPIDJSON_DIAG_POP
#endif
 
#endif // RAPIDJSON_RAPIDJSON_H_