kjs/JSImmediate.h

   1 /*
   2  *  Copyright (C) 2003, 2004, 2005, 2006, 2007 Apple Inc. All rights reserved.
   3  *  Copyright (C) 2006 Alexey Proskuryakov (ap@webkit.org)
   4  *
   5  *  This library is free software; you can redistribute it and/or
   6  *  modify it under the terms of the GNU Library General Public
   7  *  License as published by the Free Software Foundation; either
   8  *  version 2 of the License, or (at your option) any later version.
   9  *
  10  *  This library is distributed in the hope that it will be useful,
  11  *  but WITHOUT ANY WARRANTY; without even the implied warranty of
  12  *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  13  *  Library General Public License for more details.
  14  *
  15  *  You should have received a copy of the GNU Library General Public License
  16  *  along with this library; see the file COPYING.LIB.  If not, write to
  17  *  the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
  18  *  Boston, MA 02110-1301, USA.
  19  *
  20  */
  21
  22 #ifndef KJS_JS_IMMEDIATE_H
  23 #define KJS_JS_IMMEDIATE_H
  24
  25 #include "JSType.h"
  26 #include <wtf/Assertions.h>
  27 #include <wtf/AlwaysInline.h>
  28 #include <wtf/MathExtras.h>
  29 #include <limits>
  30 #include <stdarg.h>
  31 #include <stdint.h>
  32 #include <stdlib.h>
  33
  34 namespace KJS {
  35
  36 class ExecState;
  37 class JSObject;
  38 class JSValue;
  39 class UString;
  40
  41 /*
  42  * A JSValue*  is either a pointer to a cell (a heap-allocated object) or an immediate (a type-tagged
  43  * signed int masquerading as a pointer). The low two bits in a JSValue* are available
  44  * for type tagging because allocator alignment guarantees they will be 00 in cell pointers.
  45  *
  46  * For example, on a 32 bit system:
  47  *
  48  * JSCell*:       XXXXXXXXXXXXXXXXXXXXXXXXXXXXXX                 00
  49  *               [ high 30 bits: pointer address ]  [ low 2 bits -- always 0 ]
  50  *
  51  * JSImmediate:   XXXXXXXXXXXXXXXXXXXXXXXXXXXXXX                 TT
  52  *               [ high 30 bits: signed int ]       [ low 2 bits -- type tag ]
  53  *
  54  * The bit "payload" (the high 30 bits) is a 30 bit signed int for immediate numbers, a flag to distinguish true/false
  55  * and undefined/null.
  56  *
  57  * Notice that the JSType value of NullType is 4, which requires 3 bits to encode. Since we only have 2 bits
  58  * available for type tagging, we tag the null immediate with UndefinedType, and JSImmediate::type() has
  59  * to sort them out.
  60  */
  61
  62 class JSImmediate {
  63 public:
  64     static ALWAYS_INLINE bool isImmediate(const JSValue* v)
  65     {
  66         return getTag(v) != 0;
  67     }
  68
  69     static ALWAYS_INLINE bool isNumber(const JSValue* v)
  70     {
  71         return (getTag(v) == NumberType);
  72     }
  73
  74     static ALWAYS_INLINE bool isBoolean(const JSValue* v)
  75     {
  76         return (getTag(v) == BooleanType);
  77     }
  78
  79     // Since we have room for only 3 unique tags, null and undefined have to share.
  80     static ALWAYS_INLINE bool isUndefinedOrNull(const JSValue* v)
  81     {
  82         return (getTag(v) == UndefinedType);
  83     }
  84
  85     static JSValue* from(char);
  86     static JSValue* from(signed char);
  87     static JSValue* from(unsigned char);
  88     static JSValue* from(short);
  89     static JSValue* from(unsigned short);
  90     static JSValue* from(int);
  91     static JSValue* from(unsigned);
  92     static JSValue* from(long);
  93     static JSValue* from(unsigned long);
  94     static JSValue* from(long long);
  95     static JSValue* from(unsigned long long);
  96     static JSValue* from(double);
  97
  98     static ALWAYS_INLINE bool areBothImmediateNumbers(const JSValue* v1, const JSValue* v2)
  99     {
 100         return (reinterpret_cast<uintptr_t>(v1) & reinterpret_cast<uintptr_t>(v2) & TagMask) == NumberType;
 101     }
 102
 103     static ALWAYS_INLINE JSValue* andImmediateNumbers(const JSValue* v1, const JSValue* v2)
 104     {
 105         ASSERT(areBothImmediateNumbers(v1, v2));
 106         return reinterpret_cast<JSValue*>(reinterpret_cast<uintptr_t>(v1) & reinterpret_cast<uintptr_t>(v2));
 107     }
 108
 109     static double toDouble(const JSValue*);
 110     static bool toBoolean(const JSValue*);
 111     static JSObject* toObject(const JSValue*, ExecState*);
 112     static UString toString(const JSValue*);
 113     static JSType type(const JSValue*);
 114
 115     static bool getUInt32(const JSValue*, uint32_t&);
 116     static bool getTruncatedInt32(const JSValue*, int32_t&);
 117     static bool getTruncatedUInt32(const JSValue*, uint32_t&);
 118
 119     static int32_t getTruncatedInt32(const JSValue*);
 120
 121     static JSValue* trueImmediate();
 122     static JSValue* falseImmediate();
 123     static JSValue* undefinedImmediate();
 124     static JSValue* nullImmediate();
 125
 126 private:
 127     static const uintptr_t TagMask = 3; // type tags are 2 bits long
 128
 129     // Immediate values are restricted to a 30 bit signed value.
 130     static const int minImmediateInt = -(1 << 29);
 131     static const int maxImmediateInt = (1 << 29) - 1;
 132     static const unsigned maxImmediateUInt = maxImmediateInt;
 133
 134     static ALWAYS_INLINE JSValue* tag(uintptr_t bits, uintptr_t tag)
 135     {
 136         return reinterpret_cast<JSValue*>(bits | tag);
 137     }
 138
 139     static ALWAYS_INLINE uintptr_t unTag(const JSValue* v)
 140     {
 141         return reinterpret_cast<uintptr_t>(v) & ~TagMask;
 142     }
 143
 144     static ALWAYS_INLINE uintptr_t getTag(const JSValue* v)
 145     {
 146         return reinterpret_cast<uintptr_t>(v) & TagMask;
 147     }
 148 };
 149
 150 ALWAYS_INLINE JSValue* JSImmediate::trueImmediate() { return tag(1 << 2, BooleanType); }
 151 ALWAYS_INLINE JSValue* JSImmediate::falseImmediate() { return tag(0, BooleanType); }
 152 ALWAYS_INLINE JSValue* JSImmediate::undefinedImmediate() { return tag(1 << 2, UndefinedType); }
 153 ALWAYS_INLINE JSValue* JSImmediate::nullImmediate() { return tag(0, UndefinedType); }
 154
 155 ALWAYS_INLINE bool JSImmediate::toBoolean(const JSValue* v)
 156 {
 157     ASSERT(isImmediate(v));
 158     uintptr_t bits = unTag(v);
 159     return (bits != 0) & (JSImmediate::getTag(v) != UndefinedType);
 160 }
 161
 162 ALWAYS_INLINE JSValue* JSImmediate::from(char i)
 163 {
 164     return tag(i << 2, NumberType);
 165 }
 166
 167 ALWAYS_INLINE JSValue* JSImmediate::from(signed char i)
 168 {
 169     return tag(i << 2, NumberType);
 170 }
 171
 172 ALWAYS_INLINE JSValue* JSImmediate::from(unsigned char i)
 173 {
 174     return tag(i << 2, NumberType);
 175 }
 176
 177 ALWAYS_INLINE JSValue* JSImmediate::from(short i)
 178 {
 179     return tag(i << 2, NumberType);
 180 }
 181
 182 ALWAYS_INLINE JSValue* JSImmediate::from(unsigned short i)
 183 {
 184     return tag(i << 2, NumberType);
 185 }
 186
 187 ALWAYS_INLINE JSValue* JSImmediate::from(int i)
 188 {
 189     if ((i < minImmediateInt) | (i > maxImmediateInt))
 190         return 0;
 191     return tag(i << 2, NumberType);
 192 }
 193
 194 ALWAYS_INLINE JSValue* JSImmediate::from(unsigned i)
 195 {
 196     if (i > maxImmediateUInt)
 197         return 0;
 198     return tag(i << 2, NumberType);
 199 }
 200
 201 ALWAYS_INLINE JSValue* JSImmediate::from(long i)
 202 {
 203     if ((i < minImmediateInt) | (i > maxImmediateInt))
 204         return 0;
 205     return tag(i << 2, NumberType);
 206 }
 207
 208 ALWAYS_INLINE JSValue* JSImmediate::from(unsigned long i)
 209 {
 210     if (i > maxImmediateUInt)
 211         return 0;
 212     return tag(i << 2, NumberType);
 213 }
 214
 215 ALWAYS_INLINE JSValue* JSImmediate::from(long long i)
 216 {
 217     if ((i < minImmediateInt) | (i > maxImmediateInt))
 218         return 0;
 219     return tag(static_cast<uintptr_t>(i) << 2, NumberType);
 220 }
 221
 222 ALWAYS_INLINE JSValue* JSImmediate::from(unsigned long long i)
 223 {
 224     if (i > maxImmediateUInt)
 225         return 0;
 226     return tag(static_cast<uintptr_t>(i) << 2, NumberType);
 227 }
 228
 229 ALWAYS_INLINE JSValue* JSImmediate::from(double d)
 230 {
 231     const int intVal = static_cast<int>(d);
 232
 233     if ((intVal < minImmediateInt) | (intVal > maxImmediateInt))
 234         return 0;
 235
 236     // Check for data loss from conversion to int.
 237     if ((intVal != d) || (!intVal && signbit(d)))
 238         return 0;
 239
 240     return tag(intVal << 2, NumberType);
 241 }
 242
 243 ALWAYS_INLINE int32_t JSImmediate::getTruncatedInt32(const JSValue* v)
 244 {
 245     ASSERT(isNumber(v));
 246     return static_cast<int32_t>(unTag(v)) >> 2;
 247 }
 248
 249 ALWAYS_INLINE double JSImmediate::toDouble(const JSValue* v)
 250 {
 251     ASSERT(isImmediate(v));
 252     const int32_t i = static_cast<int32_t>(unTag(v)) >> 2;
 253     if (JSImmediate::getTag(v) == UndefinedType && i)
 254         return std::numeric_limits<double>::quiet_NaN();
 255     return i;
 256 }
 257
 258 ALWAYS_INLINE bool JSImmediate::getUInt32(const JSValue* v, uint32_t& i)
 259 {
 260     const int32_t si = static_cast<int32_t>(unTag(v)) >> 2;
 261     i = si;
 262     return isNumber(v) & (si >= 0);
 263 }
 264
 265 ALWAYS_INLINE bool JSImmediate::getTruncatedInt32(const JSValue* v, int32_t& i)
 266 {
 267     i = static_cast<int32_t>(unTag(v)) >> 2;
 268     return isNumber(v);
 269 }
 270
 271 ALWAYS_INLINE bool JSImmediate::getTruncatedUInt32(const JSValue* v, uint32_t& i)
 272 {
 273     return getUInt32(v, i);
 274 }
 275
 276 } // namespace KJS
 277
 278 #endif