jsimmediate.h

linux下开源浏览器WebKit的源码,市面上的很多商用浏览器都是移植自WebKit

/*
 *  Copyright (C) 2003, 2004, 2005, 2006, 2007, 2008, 2009 Apple Inc. All rights reserved.
 *  Copyright (C) 2006 Alexey Proskuryakov ([e-mail])
 *
 *  This library is free software; you can redistribute it and/or
 *  modify it under the terms of the GNU Library General Public
 *  License as published by the Free Software Foundation; either
 *  version 2 of the License, or (at your option) any later version.
 *
 *  This library is distributed in the hope that it will be useful,
 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 *  Library General Public License for more details.
 *
 *  You should have received a copy of the GNU Library General Public License
 *  along with this library; see the file COPYING.LIB.  If not, write to
 *  the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
 *  Boston, MA 02110-1301, USA.
 *
 */

#ifndef JSImmediate_h
#define JSImmediate_h

#include <wtf/Assertions.h>
#include <wtf/AlwaysInline.h>
#include <wtf/MathExtras.h>
#include <wtf/StdLibExtras.h>
#include "JSValue.h"
#include <limits>
#include <limits.h>
#include <stdarg.h>
#include <stdint.h>
#include <stdlib.h>

namespace JSC {

    class ExecState;
    class JSCell;
    class JSFastMath;
    class JSGlobalData;
    class JSObject;
    class UString;

    JSValuePtr js0();
    JSValuePtr jsNull();
    JSValuePtr jsBoolean(bool b);
    JSValuePtr jsUndefined();
    JSValuePtr jsImpossibleValue();
    JSValuePtr jsNumber(ExecState* exec, double d);
    JSValuePtr jsNumber(ExecState*, char i);
    JSValuePtr jsNumber(ExecState*, unsigned char i);
    JSValuePtr jsNumber(ExecState*, short i);
    JSValuePtr jsNumber(ExecState*, unsigned short i);
    JSValuePtr jsNumber(ExecState* exec, int i);
    JSValuePtr jsNumber(ExecState* exec, unsigned i);
    JSValuePtr jsNumber(ExecState* exec, long i);
    JSValuePtr jsNumber(ExecState* exec, unsigned long i);
    JSValuePtr jsNumber(ExecState* exec, long long i);
    JSValuePtr jsNumber(ExecState* exec, unsigned long long i);
    JSValuePtr jsNumber(JSGlobalData* globalData, double d);
    JSValuePtr jsNumber(JSGlobalData* globalData, short i);
    JSValuePtr jsNumber(JSGlobalData* globalData, unsigned short i);
    JSValuePtr jsNumber(JSGlobalData* globalData, int i);
    JSValuePtr jsNumber(JSGlobalData* globalData, unsigned i);
    JSValuePtr jsNumber(JSGlobalData* globalData, long i);
    JSValuePtr jsNumber(JSGlobalData* globalData, unsigned long i);
    JSValuePtr jsNumber(JSGlobalData* globalData, long long i);
    JSValuePtr jsNumber(JSGlobalData* globalData, unsigned long long i);

#if USE(ALTERNATE_JSIMMEDIATE)
    inline intptr_t reinterpretDoubleToIntptr(double value)
    {
        return WTF::bitwise_cast<intptr_t>(value);
    }

    inline double reinterpretIntptrToDouble(intptr_t value)
    {
        return WTF::bitwise_cast<double>(value);
    }
#endif

    /*
     * A JSValue* is either a pointer to a cell (a heap-allocated object) or an immediate (a type-tagged 
     * value masquerading as a pointer). The low two bits in a JSValue* are available for type tagging
     * because allocator alignment guarantees they will be 00 in cell pointers.
     *
     * For example, on a 32 bit system:
     *
     * JSCell*:             XXXXXXXXXXXXXXXXXXXXXXXXXXXXXX                     00
     *                      [ high 30 bits: pointer address ]  [ low 2 bits -- always 0 ]
     * JSImmediate:         XXXXXXXXXXXXXXXXXXXXXXXXXXXXXX                     TT
     *                      [ high 30 bits: 'payload' ]             [ low 2 bits -- tag ]
     *
     * Where the bottom two bits are non-zero they either indicate that the immediate is a 31 bit signed
     * integer, or they mark the value as being an immediate of a type other than integer, with a secondary
     * tag used to indicate the exact type.
     *
     * Where the lowest bit is set (TT is equal to 01 or 11) the high 31 bits form a 31 bit signed int value.
     * Where TT is equal to 10 this indicates this is a type of immediate other than an integer, and the next
     * two bits will form an extended tag.
     *
     * 31 bit signed int:   XXXXXXXXXXXXXXXXXXXXXXXXXXXXXX                     X1
     *                      [ high 30 bits of the value ]      [ high bit part of value ]
     * Other:               YYYYYYYYYYYYYYYYYYYYYYYYYYYY      ZZ               10
     *                      [ extended 'payload' ]  [  extended tag  ]  [  tag 'other'  ]
     *
     * Where the first bit of the extended tag is set this flags the value as being a boolean, and the following
     * bit would flag the value as undefined.  If neither bits are set, the value is null.
     *
     * Other:               YYYYYYYYYYYYYYYYYYYYYYYYYYYY      UB               10
     *                      [ extended 'payload' ]  [ undefined | bool ]  [ tag 'other' ]
     *
     * For boolean value the lowest bit in the payload holds the value of the bool, all remaining bits are zero.
     * For undefined or null immediates the payload is zero.
     *
     * Boolean:             000000000000000000000000000V      01               10
     *                      [ boolean value ]              [ bool ]       [ tag 'other' ]
     * Undefined:           0000000000000000000000000000      10               10
     *                      [ zero ]                    [ undefined ]     [ tag 'other' ]
     * Null:                0000000000000000000000000000      00               10
     *                      [ zero ]                       [ zero ]       [ tag 'other' ]
     */

    /*
     * On 64-bit platforms, we support an alternative encoding form for immediates, if
     * USE(ALTERNATE_JSIMMEDIATE) is defined.  When this format is used, double precision
     * floating point values may also be encoded as JSImmediates.
     *
     * The encoding makes use of unused NaN space in the IEEE754 representation.  Any value
     * with the top 13 bits set represents a QNaN (with the sign bit set).  QNaN values
     * can encode a 51-bit payload.  Hardware produced and C-library payloads typically
     * have a payload of zero.  We assume that non-zero payloads are available to encode
     * pointer and integer values.  Since any 64-bit bit pattern where the top 15 bits are
     * all set represents a NaN with a non-zero payload, we can use this space in the NaN
     * ranges to encode other values (however there are also other ranges of NaN space that
     * could have been selected).  This range of NaN space is represented by 64-bit numbers
     * begining with the 16-bit hex patterns 0xFFFE and 0xFFFF - we rely on the fact that no
     * valid double-precision numbers will begin fall in these ranges.
     *
     * The scheme we have implemented encodes double precision values by adding 2^48 to the
     * 64-bit integer representation of the number.  After this manipulation, no encoded
     * double-precision value will begin with the pattern 0x0000 or 0xFFFF.
     *
     * The top 16-bits denote the type of the encoded JSImmediate:
     *
     * Pointer: 0000:PPPP:PPPP:PPPP
     *          0001:****:****:****
     * Double:{         ...
     *          FFFE:****:****:****
     * Integer: FFFF:0000:IIII:IIII
     *
     * 32-bit signed integers are marked with the 16-bit tag 0xFFFF.  The tag 0x0000
     * denotes a pointer, or another form of tagged immediate.  Boolean, null and undefined
     * values are encoded in the same manner as the default format.
     */

    class JSImmediate {
    private:
        friend class JIT;
        friend class JSValuePtr;
        friend class JSFastMath;
        friend JSValuePtr js0();
        friend JSValuePtr jsNull();
        friend JSValuePtr jsBoolean(bool b);
        friend JSValuePtr jsUndefined();
        friend JSValuePtr jsImpossibleValue();
        friend JSValuePtr jsNumber(ExecState* exec, double d);
        friend JSValuePtr jsNumber(ExecState*, char i);
        friend JSValuePtr jsNumber(ExecState*, unsigned char i);
        friend JSValuePtr jsNumber(ExecState*, short i);
        friend JSValuePtr jsNumber(ExecState*, unsigned short i);
        friend JSValuePtr jsNumber(ExecState* exec, int i);
        friend JSValuePtr jsNumber(ExecState* exec, unsigned i);
        friend JSValuePtr jsNumber(ExecState* exec, long i);
        friend JSValuePtr jsNumber(ExecState* exec, unsigned long i);
        friend JSValuePtr jsNumber(ExecState* exec, long long i);
        friend JSValuePtr jsNumber(ExecState* exec, unsigned long long i);
        friend JSValuePtr jsNumber(JSGlobalData* globalData, double d);
        friend JSValuePtr jsNumber(JSGlobalData* globalData, short i);
        friend JSValuePtr jsNumber(JSGlobalData* globalData, unsigned short i);
        friend JSValuePtr jsNumber(JSGlobalData* globalData, int i);
        friend JSValuePtr jsNumber(JSGlobalData* globalData, unsigned i);
        friend JSValuePtr jsNumber(JSGlobalData* globalData, long i);
        friend JSValuePtr jsNumber(JSGlobalData* globalData, unsigned long i);
        friend JSValuePtr jsNumber(JSGlobalData* globalData, long long i);
        friend JSValuePtr jsNumber(JSGlobalData* globalData, unsigned long long i);

#if USE(ALTERNATE_JSIMMEDIATE)
        // If all bits in the mask are set, this indicates an integer number,
        // if any but not all are set this value is a double precision number.
        static const intptr_t TagTypeNumber = 0xffff000000000000ll;
        // This value is 2^48, used to encode doubles such that the encoded value will begin
        // with a 16-bit pattern within the range 0x0001..0xFFFE.
        static const intptr_t DoubleEncodeOffset = 0x1000000000000ll;
#else
        static const intptr_t TagTypeNumber = 0x1; // bottom bit set indicates integer, this dominates the following bit
#endif
        static const intptr_t TagBitTypeOther   = 0x2; // second bit set indicates immediate other than an integer
        static const intptr_t TagMask           = TagTypeNumber | TagBitTypeOther;

        static const intptr_t ExtendedTagMask         = 0xC; // extended tag holds a further two bits
        static const intptr_t ExtendedTagBitBool      = 0x4;
        static const intptr_t ExtendedTagBitUndefined = 0x8;

        static const intptr_t FullTagTypeMask      = TagMask | ExtendedTagMask;
        static const intptr_t FullTagTypeBool      = TagBitTypeOther | ExtendedTagBitBool;
        static const intptr_t FullTagTypeUndefined = TagBitTypeOther | ExtendedTagBitUndefined;
        static const intptr_t FullTagTypeNull      = TagBitTypeOther;

#if USE(ALTERNATE_JSIMMEDIATE)
        static const int32_t IntegerPayloadShift  = 0;
#else
        static const int32_t IntegerPayloadShift  = 1;
#endif
        static const int32_t ExtendedPayloadShift = 4;

        static const intptr_t ExtendedPayloadBitBoolValue = 1 << ExtendedPayloadShift;

        static const int32_t signBit = 0x80000000;
 
        static ALWAYS_INLINE bool isImmediate(JSValuePtr v)
        {
            return rawValue(v) & TagMask;
        }
        
        static ALWAYS_INLINE bool isNumber(JSValuePtr v)
        {
            return rawValue(v) & TagTypeNumber;
        }

        static ALWAYS_INLINE bool isIntegerNumber(JSValuePtr v)
        {
#if USE(ALTERNATE_JSIMMEDIATE)
            return (rawValue(v) & TagTypeNumber) == TagTypeNumber;
#else
            return isNumber(v);
#endif
        }

#if USE(ALTERNATE_JSIMMEDIATE)
        static ALWAYS_INLINE bool isDoubleNumber(JSValuePtr v)
        {
            return isNumber(v) && !isIntegerNumber(v);
        }
#endif

        static ALWAYS_INLINE bool isPositiveIntegerNumber(JSValuePtr v)
        {
            // A single mask to check for the sign bit and the number tag all at once.
            return (rawValue(v) & (signBit | TagTypeNumber)) == TagTypeNumber;
        }
        
        static ALWAYS_INLINE bool isBoolean(JSValuePtr v)
        {
            return (rawValue(v) & FullTagTypeMask) == FullTagTypeBool;
        }
        
        static ALWAYS_INLINE bool isUndefinedOrNull(JSValuePtr v)
        {
            // Undefined and null share the same value, bar the 'undefined' bit in the extended tag.
            return (rawValue(v) & ~ExtendedTagBitUndefined) == FullTagTypeNull;
        }

        static JSValuePtr from(char);
        static JSValuePtr from(signed char);
        static JSValuePtr from(unsigned char);
        static JSValuePtr from(short);
        static JSValuePtr from(unsigned short);
        static JSValuePtr from(int);
        static JSValuePtr from(unsigned);
        static JSValuePtr from(long);
        static JSValuePtr from(unsigned long);
        static JSValuePtr from(long long);
        static JSValuePtr from(unsigned long long);
        static JSValuePtr from(double);

        static ALWAYS_INLINE bool isEitherImmediate(JSValuePtr v1, JSValuePtr v2)
        {
            return (rawValue(v1) | rawValue(v2)) & TagMask;
        }

        static ALWAYS_INLINE bool areBothImmediate(JSValuePtr v1, JSValuePtr v2)
        {
            return isImmediate(v1) & isImmediate(v2);
        }

        static ALWAYS_INLINE bool areBothImmediateIntegerNumbers(JSValuePtr v1, JSValuePtr v2)
        {
#if USE(ALTERNATE_JSIMMEDIATE)
            return (rawValue(v1) & rawValue(v2) & TagTypeNumber) == TagTypeNumber;
#else
            return rawValue(v1) & rawValue(v2) & TagTypeNumber;
#endif
        }

        static double toDouble(JSValuePtr);
        static bool toBoolean(JSValuePtr);
        static JSObject* toObject(JSValuePtr, ExecState*);
        static JSObject* toThisObject(JSValuePtr, ExecState*);
        static UString toString(JSValuePtr);

        static bool getUInt32(JSValuePtr, uint32_t&);
        static bool getTruncatedInt32(JSValuePtr, int32_t&);
        static bool getTruncatedUInt32(JSValuePtr, uint32_t&);

        static int32_t getTruncatedInt32(JSValuePtr);
        static uint32_t getTruncatedUInt32(JSValuePtr);

        static JSValuePtr trueImmediate();
        static JSValuePtr falseImmediate();
        static JSValuePtr undefinedImmediate();
        static JSValuePtr nullImmediate();
        static JSValuePtr zeroImmediate();
        static JSValuePtr oneImmediate();

        static JSValuePtr impossibleValue();
        
        static JSObject* prototype(JSValuePtr, ExecState*);

    private:
#if USE(ALTERNATE_JSIMMEDIATE)
        static const int minImmediateInt = ((-INT_MAX) - 1);
        static const int maxImmediateInt = INT_MAX;
#else
        static const int minImmediateInt = ((-INT_MAX) - 1) >> IntegerPayloadShift;
        static const int maxImmediateInt = INT_MAX >> IntegerPayloadShift;
#endif
        static const unsigned maxImmediateUInt = maxImmediateInt;

        static ALWAYS_INLINE JSValuePtr makeValue(intptr_t integer)
        {
            return JSValuePtr::makeImmediate(integer);
        }

        // With USE(ALTERNATE_JSIMMEDIATE) we want the argument to be zero extended, so the
        // integer doesn't interfere with the tag bits in the upper word.  In the default encoding,
        // if intptr_t id larger then int32_t we sign extend the value through the upper word.
#if USE(ALTERNATE_JSIMMEDIATE)
        static ALWAYS_INLINE JSValuePtr makeInt(uint32_t value)
#else
        static ALWAYS_INLINE JSValuePtr makeInt(int32_t value)
#endif
        {
            return makeValue((static_cast<intptr_t>(value) << IntegerPayloadShift) | TagTypeNumber);
        }
        
#if USE(ALTERNATE_JSIMMEDIATE)
        static ALWAYS_INLINE JSValuePtr makeDouble(double value)
        {
            return makeValue(reinterpretDoubleToIntptr(value) + DoubleEncodeOffset);
        }
#endif
        
        static ALWAYS_INLINE JSValuePtr makeBool(bool b)
        {
            return makeValue((static_cast<intptr_t>(b) << ExtendedPayloadShift) | FullTagTypeBool);
        }
        
        static ALWAYS_INLINE JSValuePtr makeUndefined()
        {
            return makeValue(FullTagTypeUndefined);
        }
        
        static ALWAYS_INLINE JSValuePtr makeNull()
        {
            return makeValue(FullTagTypeNull);
        }

        template<typename T>
        static JSValuePtr fromNumberOutsideIntegerRange(T);

#if USE(ALTERNATE_JSIMMEDIATE)
        static ALWAYS_INLINE double doubleValue(JSValuePtr v)
        {
            return reinterpretIntptrToDouble(rawValue(v) - DoubleEncodeOffset);
        }
#endif

        static ALWAYS_INLINE int32_t intValue(JSValuePtr v)
        {
            return static_cast<int32_t>(rawValue(v) >> IntegerPayloadShift);
        }
        
        static ALWAYS_INLINE uint32_t uintValue(JSValuePtr v)
        {
            return static_cast<uint32_t>(rawValue(v) >> IntegerPayloadShift);
        }
        
        static ALWAYS_INLINE bool boolValue(JSValuePtr v)
        {
            return rawValue(v) & ExtendedPayloadBitBoolValue;
        }
        
        static ALWAYS_INLINE intptr_t rawValue(JSValuePtr v)
        {
            return v.immediateValue();
        }

        static double nonInlineNaN();
    };

    ALWAYS_INLINE JSValuePtr JSImmediate::trueImmediate() { return makeBool(true); }
    ALWAYS_INLINE JSValuePtr JSImmediate::falseImmediate() { return makeBool(false); }
    ALWAYS_INLINE JSValuePtr JSImmediate::undefinedImmediate() { return makeUndefined(); }
    ALWAYS_INLINE JSValuePtr JSImmediate::nullImmediate() { return makeNull(); }
    ALWAYS_INLINE JSValuePtr JSImmediate::zeroImmediate() { return makeInt(0); }
    ALWAYS_INLINE JSValuePtr JSImmediate::oneImmediate() { return makeInt(1); }

    // This value is impossible because 0x4 is not a valid pointer but a tag of 0 would indicate non-immediate
    ALWAYS_INLINE JSValuePtr JSImmediate::impossibleValue() { return makeValue(0x4); }

#if USE(ALTERNATE_JSIMMEDIATE)
    inline bool doubleToBoolean(double value)
    {
        return value < 0.0 || value > 0.0;
    }

    ALWAYS_INLINE bool JSImmediate::toBoolean(JSValuePtr v)