The Tor Browser: js/public/Value.h@925c144e1f1f (annotated)

js/public/Value.h@925c144e1f1f (annotated)

js/public/Value.h

Fri, 16 Jan 2015 18:13:44 +0100

author: Michael Schloh von Bennewitz <michael@schloh.com>
date: Fri, 16 Jan 2015 18:13:44 +0100
branch: TOR_BUG_9701
changeset 14: 925c144e1f1f
permissions: -rw-r--r--

Integrate suggestion from review to improve consistency with existing code.

 /* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*-
  * vim: set ts=8 sts=4 et sw=4 tw=99:
  * This Source Code Form is subject to the terms of the Mozilla Public
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 /* JS::Value implementation. */
 #ifndef js_Value_h
 #define js_Value_h
 #include "mozilla/Attributes.h"
 #include "mozilla/FloatingPoint.h"
 #include "mozilla/Likely.h"
 #include <limits> /* for std::numeric_limits */
 #include "jstypes.h"
 #include "js/Anchor.h"
 #include "js/RootingAPI.h"
 #include "js/Utility.h"
 namespace JS { class Value; }
 /* JS::Value can store a full int32_t. */
 #define JSVAL_INT_BITS          32
 #define JSVAL_INT_MIN           ((int32_t)0x80000000)
 #define JSVAL_INT_MAX           ((int32_t)0x7fffffff)
 /*
  * Try to get jsvals 64-bit aligned. We could almost assert that all values are
  * aligned, but MSVC and GCC occasionally break alignment.
  */
 #if defined(__GNUC__) || defined(__xlc__) || defined(__xlC__)
 # define JSVAL_ALIGNMENT        __attribute__((aligned (8)))
 #elif defined(_MSC_VER)
   /*
    * Structs can be aligned with MSVC, but not if they are used as parameters,
    * so we just don't try to align.
    */
 # define JSVAL_ALIGNMENT
 #elif defined(__SUNPRO_C) || defined(__SUNPRO_CC)
 # define JSVAL_ALIGNMENT
 #elif defined(__HP_cc) || defined(__HP_aCC)
 # define JSVAL_ALIGNMENT
 #endif
 #if JS_BITS_PER_WORD == 64
 # define JSVAL_TAG_SHIFT 47
 #endif
 /*
  * We try to use enums so that printing a jsval_layout in the debugger shows
  * nice symbolic type tags, however we can only do this when we can force the
  * underlying type of the enum to be the desired size.
  */
 #if !defined(__SUNPRO_CC) && !defined(__xlC__)
 #if defined(_MSC_VER)
 # define JS_ENUM_HEADER(id, type)              enum id : type
 # define JS_ENUM_FOOTER(id)
 #else
 # define JS_ENUM_HEADER(id, type)              enum id
 # define JS_ENUM_FOOTER(id)                    __attribute__((packed))
 #endif
 /* Remember to propagate changes to the C defines below. */
 JS_ENUM_HEADER(JSValueType, uint8_t)
 {
     JSVAL_TYPE_DOUBLE              = 0x00,
     JSVAL_TYPE_INT32               = 0x01,
     JSVAL_TYPE_UNDEFINED           = 0x02,
     JSVAL_TYPE_BOOLEAN             = 0x03,
     JSVAL_TYPE_MAGIC               = 0x04,
     JSVAL_TYPE_STRING              = 0x05,
     JSVAL_TYPE_NULL                = 0x06,
     JSVAL_TYPE_OBJECT              = 0x07,
     /* These never appear in a jsval; they are only provided as an out-of-band value. */
     JSVAL_TYPE_UNKNOWN             = 0x20,
     JSVAL_TYPE_MISSING             = 0x21
 } JS_ENUM_FOOTER(JSValueType);
 JS_STATIC_ASSERT(sizeof(JSValueType) == 1);
 #if JS_BITS_PER_WORD == 32
 /* Remember to propagate changes to the C defines below. */
 JS_ENUM_HEADER(JSValueTag, uint32_t)
 {
     JSVAL_TAG_CLEAR                = 0xFFFFFF80,
     JSVAL_TAG_INT32                = JSVAL_TAG_CLEAR | JSVAL_TYPE_INT32,
     JSVAL_TAG_UNDEFINED            = JSVAL_TAG_CLEAR | JSVAL_TYPE_UNDEFINED,
     JSVAL_TAG_STRING               = JSVAL_TAG_CLEAR | JSVAL_TYPE_STRING,
     JSVAL_TAG_BOOLEAN              = JSVAL_TAG_CLEAR | JSVAL_TYPE_BOOLEAN,
     JSVAL_TAG_MAGIC                = JSVAL_TAG_CLEAR | JSVAL_TYPE_MAGIC,
     JSVAL_TAG_NULL                 = JSVAL_TAG_CLEAR | JSVAL_TYPE_NULL,
     JSVAL_TAG_OBJECT               = JSVAL_TAG_CLEAR | JSVAL_TYPE_OBJECT
 } JS_ENUM_FOOTER(JSValueTag);
 JS_STATIC_ASSERT(sizeof(JSValueTag) == 4);
 #elif JS_BITS_PER_WORD == 64
 /* Remember to propagate changes to the C defines below. */
 JS_ENUM_HEADER(JSValueTag, uint32_t)
 {
     JSVAL_TAG_MAX_DOUBLE           = 0x1FFF0,
     JSVAL_TAG_INT32                = JSVAL_TAG_MAX_DOUBLE | JSVAL_TYPE_INT32,
     JSVAL_TAG_UNDEFINED            = JSVAL_TAG_MAX_DOUBLE | JSVAL_TYPE_UNDEFINED,
     JSVAL_TAG_STRING               = JSVAL_TAG_MAX_DOUBLE | JSVAL_TYPE_STRING,
     JSVAL_TAG_BOOLEAN              = JSVAL_TAG_MAX_DOUBLE | JSVAL_TYPE_BOOLEAN,
     JSVAL_TAG_MAGIC                = JSVAL_TAG_MAX_DOUBLE | JSVAL_TYPE_MAGIC,
     JSVAL_TAG_NULL                 = JSVAL_TAG_MAX_DOUBLE | JSVAL_TYPE_NULL,
     JSVAL_TAG_OBJECT               = JSVAL_TAG_MAX_DOUBLE | JSVAL_TYPE_OBJECT
 } JS_ENUM_FOOTER(JSValueTag);
 JS_STATIC_ASSERT(sizeof(JSValueTag) == sizeof(uint32_t));
 JS_ENUM_HEADER(JSValueShiftedTag, uint64_t)
 {
     JSVAL_SHIFTED_TAG_MAX_DOUBLE   = ((((uint64_t)JSVAL_TAG_MAX_DOUBLE) << JSVAL_TAG_SHIFT) | 0xFFFFFFFF),
     JSVAL_SHIFTED_TAG_INT32        = (((uint64_t)JSVAL_TAG_INT32)      << JSVAL_TAG_SHIFT),
     JSVAL_SHIFTED_TAG_UNDEFINED    = (((uint64_t)JSVAL_TAG_UNDEFINED)  << JSVAL_TAG_SHIFT),
     JSVAL_SHIFTED_TAG_STRING       = (((uint64_t)JSVAL_TAG_STRING)     << JSVAL_TAG_SHIFT),
     JSVAL_SHIFTED_TAG_BOOLEAN      = (((uint64_t)JSVAL_TAG_BOOLEAN)    << JSVAL_TAG_SHIFT),
     JSVAL_SHIFTED_TAG_MAGIC        = (((uint64_t)JSVAL_TAG_MAGIC)      << JSVAL_TAG_SHIFT),
     JSVAL_SHIFTED_TAG_NULL         = (((uint64_t)JSVAL_TAG_NULL)       << JSVAL_TAG_SHIFT),
     JSVAL_SHIFTED_TAG_OBJECT       = (((uint64_t)JSVAL_TAG_OBJECT)     << JSVAL_TAG_SHIFT)
 } JS_ENUM_FOOTER(JSValueShiftedTag);
 JS_STATIC_ASSERT(sizeof(JSValueShiftedTag) == sizeof(uint64_t));
 #endif
 #else  /* !defined(__SUNPRO_CC) && !defined(__xlC__) */
 typedef uint8_t JSValueType;
 #define JSVAL_TYPE_DOUBLE            ((uint8_t)0x00)
 #define JSVAL_TYPE_INT32             ((uint8_t)0x01)
 #define JSVAL_TYPE_UNDEFINED         ((uint8_t)0x02)
 #define JSVAL_TYPE_BOOLEAN           ((uint8_t)0x03)
 #define JSVAL_TYPE_MAGIC             ((uint8_t)0x04)
 #define JSVAL_TYPE_STRING            ((uint8_t)0x05)
 #define JSVAL_TYPE_NULL              ((uint8_t)0x06)
 #define JSVAL_TYPE_OBJECT            ((uint8_t)0x07)
 #define JSVAL_TYPE_UNKNOWN           ((uint8_t)0x20)
 #if JS_BITS_PER_WORD == 32
 typedef uint32_t JSValueTag;
 #define JSVAL_TAG_CLEAR              ((uint32_t)(0xFFFFFF80))
 #define JSVAL_TAG_INT32              ((uint32_t)(JSVAL_TAG_CLEAR | JSVAL_TYPE_INT32))
 #define JSVAL_TAG_UNDEFINED          ((uint32_t)(JSVAL_TAG_CLEAR | JSVAL_TYPE_UNDEFINED))
 #define JSVAL_TAG_STRING             ((uint32_t)(JSVAL_TAG_CLEAR | JSVAL_TYPE_STRING))
 #define JSVAL_TAG_BOOLEAN            ((uint32_t)(JSVAL_TAG_CLEAR | JSVAL_TYPE_BOOLEAN))
 #define JSVAL_TAG_MAGIC              ((uint32_t)(JSVAL_TAG_CLEAR | JSVAL_TYPE_MAGIC))
 #define JSVAL_TAG_NULL               ((uint32_t)(JSVAL_TAG_CLEAR | JSVAL_TYPE_NULL))
 #define JSVAL_TAG_OBJECT             ((uint32_t)(JSVAL_TAG_CLEAR | JSVAL_TYPE_OBJECT))
 #elif JS_BITS_PER_WORD == 64
 typedef uint32_t JSValueTag;
 #define JSVAL_TAG_MAX_DOUBLE         ((uint32_t)(0x1FFF0))
 #define JSVAL_TAG_INT32              (uint32_t)(JSVAL_TAG_MAX_DOUBLE | JSVAL_TYPE_INT32)
 #define JSVAL_TAG_UNDEFINED          (uint32_t)(JSVAL_TAG_MAX_DOUBLE | JSVAL_TYPE_UNDEFINED)
 #define JSVAL_TAG_STRING             (uint32_t)(JSVAL_TAG_MAX_DOUBLE | JSVAL_TYPE_STRING)
 #define JSVAL_TAG_BOOLEAN            (uint32_t)(JSVAL_TAG_MAX_DOUBLE | JSVAL_TYPE_BOOLEAN)
 #define JSVAL_TAG_MAGIC              (uint32_t)(JSVAL_TAG_MAX_DOUBLE | JSVAL_TYPE_MAGIC)
 #define JSVAL_TAG_NULL               (uint32_t)(JSVAL_TAG_MAX_DOUBLE | JSVAL_TYPE_NULL)
 #define JSVAL_TAG_OBJECT             (uint32_t)(JSVAL_TAG_MAX_DOUBLE | JSVAL_TYPE_OBJECT)
 typedef uint64_t JSValueShiftedTag;
 #define JSVAL_SHIFTED_TAG_MAX_DOUBLE ((((uint64_t)JSVAL_TAG_MAX_DOUBLE) << JSVAL_TAG_SHIFT) | 0xFFFFFFFF)
 #define JSVAL_SHIFTED_TAG_INT32      (((uint64_t)JSVAL_TAG_INT32)      << JSVAL_TAG_SHIFT)
 #define JSVAL_SHIFTED_TAG_UNDEFINED  (((uint64_t)JSVAL_TAG_UNDEFINED)  << JSVAL_TAG_SHIFT)
 #define JSVAL_SHIFTED_TAG_STRING     (((uint64_t)JSVAL_TAG_STRING)     << JSVAL_TAG_SHIFT)
 #define JSVAL_SHIFTED_TAG_BOOLEAN    (((uint64_t)JSVAL_TAG_BOOLEAN)    << JSVAL_TAG_SHIFT)
 #define JSVAL_SHIFTED_TAG_MAGIC      (((uint64_t)JSVAL_TAG_MAGIC)      << JSVAL_TAG_SHIFT)
 #define JSVAL_SHIFTED_TAG_NULL       (((uint64_t)JSVAL_TAG_NULL)       << JSVAL_TAG_SHIFT)
 #define JSVAL_SHIFTED_TAG_OBJECT     (((uint64_t)JSVAL_TAG_OBJECT)     << JSVAL_TAG_SHIFT)
 #endif  /* JS_BITS_PER_WORD */
 #endif  /* !defined(__SUNPRO_CC) && !defined(__xlC__) */
 #define JSVAL_LOWER_INCL_TYPE_OF_OBJ_OR_NULL_SET        JSVAL_TYPE_NULL
 #define JSVAL_UPPER_EXCL_TYPE_OF_PRIMITIVE_SET          JSVAL_TYPE_OBJECT
 #define JSVAL_UPPER_INCL_TYPE_OF_NUMBER_SET             JSVAL_TYPE_INT32
 #define JSVAL_LOWER_INCL_TYPE_OF_PTR_PAYLOAD_SET        JSVAL_TYPE_MAGIC
 #if JS_BITS_PER_WORD == 32
 #define JSVAL_TYPE_TO_TAG(type)      ((JSValueTag)(JSVAL_TAG_CLEAR | (type)))
 #define JSVAL_LOWER_INCL_TAG_OF_OBJ_OR_NULL_SET         JSVAL_TAG_NULL
 #define JSVAL_UPPER_EXCL_TAG_OF_PRIMITIVE_SET           JSVAL_TAG_OBJECT
 #define JSVAL_UPPER_INCL_TAG_OF_NUMBER_SET              JSVAL_TAG_INT32
 #define JSVAL_LOWER_INCL_TAG_OF_GCTHING_SET             JSVAL_TAG_STRING
 #elif JS_BITS_PER_WORD == 64
 #define JSVAL_PAYLOAD_MASK           0x00007FFFFFFFFFFFLL
 #define JSVAL_TAG_MASK               0xFFFF800000000000LL
 #define JSVAL_TYPE_TO_TAG(type)      ((JSValueTag)(JSVAL_TAG_MAX_DOUBLE | (type)))
 #define JSVAL_TYPE_TO_SHIFTED_TAG(type) (((uint64_t)JSVAL_TYPE_TO_TAG(type)) << JSVAL_TAG_SHIFT)
 #define JSVAL_LOWER_INCL_TAG_OF_OBJ_OR_NULL_SET         JSVAL_TAG_NULL
 #define JSVAL_UPPER_EXCL_TAG_OF_PRIMITIVE_SET           JSVAL_TAG_OBJECT
 #define JSVAL_UPPER_INCL_TAG_OF_NUMBER_SET              JSVAL_TAG_INT32
 #define JSVAL_LOWER_INCL_TAG_OF_GCTHING_SET             JSVAL_TAG_STRING
 #define JSVAL_LOWER_INCL_SHIFTED_TAG_OF_OBJ_OR_NULL_SET  JSVAL_SHIFTED_TAG_NULL
 #define JSVAL_UPPER_EXCL_SHIFTED_TAG_OF_PRIMITIVE_SET    JSVAL_SHIFTED_TAG_OBJECT
 #define JSVAL_UPPER_EXCL_SHIFTED_TAG_OF_NUMBER_SET       JSVAL_SHIFTED_TAG_UNDEFINED
 #define JSVAL_LOWER_INCL_SHIFTED_TAG_OF_GCTHING_SET      JSVAL_SHIFTED_TAG_STRING
 #endif /* JS_BITS_PER_WORD */
 typedef enum JSWhyMagic
 {
     JS_ELEMENTS_HOLE,            /* a hole in a native object's elements */
     JS_NATIVE_ENUMERATE,         /* indicates that a custom enumerate hook forwarded
                                   * to JS_EnumerateState, which really means the object can be
                                   * enumerated like a native object. */
     JS_NO_ITER_VALUE,            /* there is not a pending iterator value */
     JS_GENERATOR_CLOSING,        /* exception value thrown when closing a generator */
     JS_NO_CONSTANT,              /* compiler sentinel value */
     JS_THIS_POISON,              /* used in debug builds to catch tracing errors */
     JS_ARG_POISON,               /* used in debug builds to catch tracing errors */
     JS_SERIALIZE_NO_NODE,        /* an empty subnode in the AST serializer */
     JS_LAZY_ARGUMENTS,           /* lazy arguments value on the stack */
     JS_OPTIMIZED_ARGUMENTS,      /* optimized-away 'arguments' value */
     JS_IS_CONSTRUCTING,          /* magic value passed to natives to indicate construction */
     JS_OVERWRITTEN_CALLEE,       /* arguments.callee has been overwritten */
     JS_BLOCK_NEEDS_CLONE,        /* value of static block object slot */
     JS_HASH_KEY_EMPTY,           /* see class js::HashableValue */
     JS_ION_ERROR,                /* error while running Ion code */
     JS_ION_BAILOUT,              /* status code to signal EnterIon will OSR into Interpret */
     JS_OPTIMIZED_OUT,            /* optimized out slot */
     JS_GENERIC_MAGIC             /* for local use */
 } JSWhyMagic;
 #if defined(IS_LITTLE_ENDIAN)
 # if JS_BITS_PER_WORD == 32
 typedef union jsval_layout
 {
     uint64_t asBits;
     struct {
         union {
             int32_t        i32;
             uint32_t       u32;
             uint32_t       boo;     // Don't use |bool| -- it must be four bytes.
             JSString       *str;
             JSObject       *obj;
             void           *ptr;
             JSWhyMagic     why;
             size_t         word;
             uintptr_t      uintptr;
         } payload;
         JSValueTag tag;
     } s;
     double asDouble;
     void *asPtr;
 } JSVAL_ALIGNMENT jsval_layout;
 # elif JS_BITS_PER_WORD == 64
 typedef union jsval_layout
 {
     uint64_t asBits;
 #if !defined(_WIN64)
     /* MSVC does not pack these correctly :-( */
     struct {
         uint64_t           payload47 : 47;
         JSValueTag         tag : 17;
     } debugView;
 #endif
     struct {
         union {
             int32_t        i32;
             uint32_t       u32;
             JSWhyMagic     why;
         } payload;
     } s;
     double asDouble;
     void *asPtr;
     size_t asWord;
     uintptr_t asUIntPtr;
 } JSVAL_ALIGNMENT jsval_layout;
 # endif  /* JS_BITS_PER_WORD */
 #else   /* defined(IS_LITTLE_ENDIAN) */
 # if JS_BITS_PER_WORD == 32
 typedef union jsval_layout
 {
     uint64_t asBits;
     struct {
         JSValueTag tag;
         union {
             int32_t        i32;
             uint32_t       u32;
             uint32_t       boo;     // Don't use |bool| -- it must be four bytes.
             JSString       *str;
             JSObject       *obj;
             void           *ptr;
             JSWhyMagic     why;
             size_t         word;
             uintptr_t      uintptr;
         } payload;
     } s;
     double asDouble;
     void *asPtr;
 } JSVAL_ALIGNMENT jsval_layout;
 # elif JS_BITS_PER_WORD == 64
 typedef union jsval_layout
 {
     uint64_t asBits;
     struct {
         JSValueTag         tag : 17;
         uint64_t           payload47 : 47;
     } debugView;
     struct {
         uint32_t           padding;
         union {
             int32_t        i32;
             uint32_t       u32;
             JSWhyMagic     why;
         } payload;
     } s;
     double asDouble;
     void *asPtr;
     size_t asWord;
     uintptr_t asUIntPtr;
 } JSVAL_ALIGNMENT jsval_layout;
 # endif /* JS_BITS_PER_WORD */
 #endif  /* defined(IS_LITTLE_ENDIAN) */
 JS_STATIC_ASSERT(sizeof(jsval_layout) == 8);
 /*
  * For codesize purposes on some platforms, it's important that the
  * compiler know that JS::Values constructed from constant values can be
  * folded to constant bit patterns at compile time, rather than
  * constructed at runtime.  Doing this requires a fair amount of C++11
  * features, which are not supported on all of our compilers.  Set up
  * some defines and helper macros in an attempt to confine the ugliness
  * here, rather than scattering it all about the file.  The important
  * features are:
  *
  * - constexpr;
  * - defaulted functions;
  * - C99-style designated initializers.
  */
 #if defined(__clang__)
 #  if __has_feature(cxx_constexpr) && __has_feature(cxx_defaulted_functions)
 #    define JS_VALUE_IS_CONSTEXPR
 #  endif
 #elif defined(__GNUC__)
 /*
  * We need 4.5 for defaulted functions, 4.6 for constexpr, 4.7 because 4.6
  * doesn't understand |(X) { .field = ... }| syntax, and 4.7.3 because
  * versions prior to that have bugs in the C++ front-end that cause crashes.
  */
 #  if MOZ_GCC_VERSION_AT_LEAST(4, 7, 3)
 #    define JS_VALUE_IS_CONSTEXPR
 #  endif
 #endif
 #if defined(JS_VALUE_IS_CONSTEXPR)
 #  define JS_RETURN_LAYOUT_FROM_BITS(BITS) \
     return (jsval_layout) { .asBits = (BITS) }
 #  define JS_VALUE_CONSTEXPR MOZ_CONSTEXPR
 #  define JS_VALUE_CONSTEXPR_VAR MOZ_CONSTEXPR_VAR
 #else
 #  define JS_RETURN_LAYOUT_FROM_BITS(BITS) \
     jsval_layout l;                        \
     l.asBits = (BITS);                     \
     return l;
 #  define JS_VALUE_CONSTEXPR
 #  define JS_VALUE_CONSTEXPR_VAR const
 #endif
 #if JS_BITS_PER_WORD == 32
 /*
  * N.B. GCC, in some but not all cases, chooses to emit signed comparison of
  * JSValueTag even though its underlying type has been forced to be uint32_t.
  * Thus, all comparisons should explicitly cast operands to uint32_t.
  */
 static inline JS_VALUE_CONSTEXPR jsval_layout
 BUILD_JSVAL(JSValueTag tag, uint32_t payload)
 {
     JS_RETURN_LAYOUT_FROM_BITS((((uint64_t)(uint32_t)tag) << 32) | payload);
 }
 static inline bool
 JSVAL_IS_DOUBLE_IMPL(jsval_layout l)
 {
     return (uint32_t)l.s.tag <= (uint32_t)JSVAL_TAG_CLEAR;
 }
 static inline jsval_layout
 DOUBLE_TO_JSVAL_IMPL(double d)
 {
     jsval_layout l;
     l.asDouble = d;
     MOZ_ASSERT(JSVAL_IS_DOUBLE_IMPL(l));
     return l;
 }
 static inline bool
 JSVAL_IS_INT32_IMPL(jsval_layout l)
 {
     return l.s.tag == JSVAL_TAG_INT32;
 }
 static inline int32_t
 JSVAL_TO_INT32_IMPL(jsval_layout l)
 {
     return l.s.payload.i32;
 }
 static inline JS_VALUE_CONSTEXPR jsval_layout
 INT32_TO_JSVAL_IMPL(int32_t i)
 {
 #if defined(JS_VALUE_IS_CONSTEXPR)
     return BUILD_JSVAL(JSVAL_TAG_INT32, i);
 #else
     jsval_layout l;
     l.s.tag = JSVAL_TAG_INT32;
     l.s.payload.i32 = i;
     return l;
 #endif
 }
 static inline bool
 JSVAL_IS_NUMBER_IMPL(jsval_layout l)
 {
     JSValueTag tag = l.s.tag;
     MOZ_ASSERT(tag != JSVAL_TAG_CLEAR);
     return (uint32_t)tag <= (uint32_t)JSVAL_UPPER_INCL_TAG_OF_NUMBER_SET;
 }
 static inline bool
 JSVAL_IS_UNDEFINED_IMPL(jsval_layout l)
 {
     return l.s.tag == JSVAL_TAG_UNDEFINED;
 }
 static inline bool
 JSVAL_IS_STRING_IMPL(jsval_layout l)
 {
     return l.s.tag == JSVAL_TAG_STRING;
 }
 static inline jsval_layout
 STRING_TO_JSVAL_IMPL(JSString *str)
 {
     jsval_layout l;
     MOZ_ASSERT(uintptr_t(str) > 0x1000);
     l.s.tag = JSVAL_TAG_STRING;
     l.s.payload.str = str;
     return l;
 }
 static inline JSString *
 JSVAL_TO_STRING_IMPL(jsval_layout l)
 {
     return l.s.payload.str;
 }
 static inline bool
 JSVAL_IS_BOOLEAN_IMPL(jsval_layout l)
 {
     return l.s.tag == JSVAL_TAG_BOOLEAN;
 }
 static inline bool
 JSVAL_TO_BOOLEAN_IMPL(jsval_layout l)
 {
     return l.s.payload.boo;
 }
 static inline jsval_layout
 BOOLEAN_TO_JSVAL_IMPL(bool b)
 {
     jsval_layout l;
     l.s.tag = JSVAL_TAG_BOOLEAN;
     l.s.payload.boo = b;
     return l;
 }
 static inline bool
 JSVAL_IS_MAGIC_IMPL(jsval_layout l)
 {
     return l.s.tag == JSVAL_TAG_MAGIC;
 }
 static inline bool
 JSVAL_IS_OBJECT_IMPL(jsval_layout l)
 {
     return l.s.tag == JSVAL_TAG_OBJECT;
 }
 static inline bool
 JSVAL_IS_PRIMITIVE_IMPL(jsval_layout l)
 {
     return (uint32_t)l.s.tag < (uint32_t)JSVAL_UPPER_EXCL_TAG_OF_PRIMITIVE_SET;
 }
 static inline bool
 JSVAL_IS_OBJECT_OR_NULL_IMPL(jsval_layout l)
 {
     MOZ_ASSERT((uint32_t)l.s.tag <= (uint32_t)JSVAL_TAG_OBJECT);
     return (uint32_t)l.s.tag >= (uint32_t)JSVAL_LOWER_INCL_TAG_OF_OBJ_OR_NULL_SET;
 }
 static inline JSObject *
 JSVAL_TO_OBJECT_IMPL(jsval_layout l)
 {
     return l.s.payload.obj;
 }
 static inline jsval_layout
 OBJECT_TO_JSVAL_IMPL(JSObject *obj)
 {
     jsval_layout l;
     MOZ_ASSERT(uintptr_t(obj) > 0x1000 || uintptr_t(obj) == 0x42);
     l.s.tag = JSVAL_TAG_OBJECT;
     l.s.payload.obj = obj;
     return l;
 }
 static inline bool
 JSVAL_IS_NULL_IMPL(jsval_layout l)
 {
     return l.s.tag == JSVAL_TAG_NULL;
 }
 static inline jsval_layout
 PRIVATE_PTR_TO_JSVAL_IMPL(void *ptr)
 {
     jsval_layout l;
     MOZ_ASSERT(((uint32_t)ptr & 1) == 0);
     l.s.tag = (JSValueTag)0;
     l.s.payload.ptr = ptr;
     MOZ_ASSERT(JSVAL_IS_DOUBLE_IMPL(l));
     return l;
 }
 static inline void *
 JSVAL_TO_PRIVATE_PTR_IMPL(jsval_layout l)
 {
     return l.s.payload.ptr;
 }
 static inline bool
 JSVAL_IS_GCTHING_IMPL(jsval_layout l)
 {
     /* gcc sometimes generates signed < without explicit casts. */
     return (uint32_t)l.s.tag >= (uint32_t)JSVAL_LOWER_INCL_TAG_OF_GCTHING_SET;
 }
 static inline void *
 JSVAL_TO_GCTHING_IMPL(jsval_layout l)
 {
     return l.s.payload.ptr;
 }
 static inline bool
 JSVAL_IS_TRACEABLE_IMPL(jsval_layout l)
 {
     return l.s.tag == JSVAL_TAG_STRING || l.s.tag == JSVAL_TAG_OBJECT;
 }
 static inline uint32_t
 JSVAL_TRACE_KIND_IMPL(jsval_layout l)
 {
     return (uint32_t)(bool)JSVAL_IS_STRING_IMPL(l);
 }
 static inline bool
 JSVAL_IS_SPECIFIC_INT32_IMPL(jsval_layout l, int32_t i32)
 {
     return l.s.tag == JSVAL_TAG_INT32 && l.s.payload.i32 == i32;
 }
 static inline bool
 JSVAL_IS_SPECIFIC_BOOLEAN(jsval_layout l, bool b)
 {
     return (l.s.tag == JSVAL_TAG_BOOLEAN) && (l.s.payload.boo == uint32_t(b));
 }
 static inline jsval_layout
 MAGIC_TO_JSVAL_IMPL(JSWhyMagic why)
 {
     jsval_layout l;
     l.s.tag = JSVAL_TAG_MAGIC;
     l.s.payload.why = why;
     return l;
 }
 static inline jsval_layout
 MAGIC_UINT32_TO_JSVAL_IMPL(uint32_t payload)
 {
     jsval_layout l;
     l.s.tag = JSVAL_TAG_MAGIC;
     l.s.payload.u32 = payload;
     return l;
 }
 static inline bool
 JSVAL_SAME_TYPE_IMPL(jsval_layout lhs, jsval_layout rhs)
 {
     JSValueTag ltag = lhs.s.tag, rtag = rhs.s.tag;
     return ltag == rtag || (ltag < JSVAL_TAG_CLEAR && rtag < JSVAL_TAG_CLEAR);
 }
 static inline JSValueType
 JSVAL_EXTRACT_NON_DOUBLE_TYPE_IMPL(jsval_layout l)
 {
     uint32_t type = l.s.tag & 0xF;
     MOZ_ASSERT(type > JSVAL_TYPE_DOUBLE);
     return (JSValueType)type;
 }
 #elif JS_BITS_PER_WORD == 64
 static inline JS_VALUE_CONSTEXPR jsval_layout
 BUILD_JSVAL(JSValueTag tag, uint64_t payload)
 {
     JS_RETURN_LAYOUT_FROM_BITS((((uint64_t)(uint32_t)tag) << JSVAL_TAG_SHIFT) | payload);
 }
 static inline bool
 JSVAL_IS_DOUBLE_IMPL(jsval_layout l)
 {
     return l.asBits <= JSVAL_SHIFTED_TAG_MAX_DOUBLE;
 }
 static inline jsval_layout
 DOUBLE_TO_JSVAL_IMPL(double d)
 {
     jsval_layout l;
     l.asDouble = d;
     MOZ_ASSERT(l.asBits <= JSVAL_SHIFTED_TAG_MAX_DOUBLE);
     return l;
 }
 static inline bool
 JSVAL_IS_INT32_IMPL(jsval_layout l)
 {
     return (uint32_t)(l.asBits >> JSVAL_TAG_SHIFT) == JSVAL_TAG_INT32;
 }
 static inline int32_t
 JSVAL_TO_INT32_IMPL(jsval_layout l)
 {
     return (int32_t)l.asBits;
 }
 static inline JS_VALUE_CONSTEXPR jsval_layout
 INT32_TO_JSVAL_IMPL(int32_t i32)
 {
     JS_RETURN_LAYOUT_FROM_BITS(((uint64_t)(uint32_t)i32) | JSVAL_SHIFTED_TAG_INT32);
 }
 static inline bool
 JSVAL_IS_NUMBER_IMPL(jsval_layout l)
 {
     return l.asBits < JSVAL_UPPER_EXCL_SHIFTED_TAG_OF_NUMBER_SET;
 }
 static inline bool
 JSVAL_IS_UNDEFINED_IMPL(jsval_layout l)
 {
     return l.asBits == JSVAL_SHIFTED_TAG_UNDEFINED;
 }
 static inline bool
 JSVAL_IS_STRING_IMPL(jsval_layout l)
 {
     return (uint32_t)(l.asBits >> JSVAL_TAG_SHIFT) == JSVAL_TAG_STRING;
 }
 static inline jsval_layout
 STRING_TO_JSVAL_IMPL(JSString *str)
 {
     jsval_layout l;
     uint64_t strBits = (uint64_t)str;
     MOZ_ASSERT(uintptr_t(str) > 0x1000);
     MOZ_ASSERT((strBits >> JSVAL_TAG_SHIFT) == 0);
     l.asBits = strBits | JSVAL_SHIFTED_TAG_STRING;
     return l;
 }
 static inline JSString *
 JSVAL_TO_STRING_IMPL(jsval_layout l)
 {
     return (JSString *)(l.asBits & JSVAL_PAYLOAD_MASK);
 }
 static inline bool
 JSVAL_IS_BOOLEAN_IMPL(jsval_layout l)
 {
     return (uint32_t)(l.asBits >> JSVAL_TAG_SHIFT) == JSVAL_TAG_BOOLEAN;
 }
 static inline bool
 JSVAL_TO_BOOLEAN_IMPL(jsval_layout l)
 {
     return (bool)(l.asBits & JSVAL_PAYLOAD_MASK);
 }
 static inline jsval_layout
 BOOLEAN_TO_JSVAL_IMPL(bool b)
 {
     jsval_layout l;
     l.asBits = ((uint64_t)(uint32_t)b) | JSVAL_SHIFTED_TAG_BOOLEAN;
     return l;
 }
 static inline bool
 JSVAL_IS_MAGIC_IMPL(jsval_layout l)
 {
     return (l.asBits >> JSVAL_TAG_SHIFT) == JSVAL_TAG_MAGIC;
 }
 static inline bool
 JSVAL_IS_PRIMITIVE_IMPL(jsval_layout l)
 {
     return l.asBits < JSVAL_UPPER_EXCL_SHIFTED_TAG_OF_PRIMITIVE_SET;
 }
 static inline bool
 JSVAL_IS_OBJECT_IMPL(jsval_layout l)
 {
     MOZ_ASSERT((l.asBits >> JSVAL_TAG_SHIFT) <= JSVAL_TAG_OBJECT);
     return l.asBits >= JSVAL_SHIFTED_TAG_OBJECT;
 }
 static inline bool
 JSVAL_IS_OBJECT_OR_NULL_IMPL(jsval_layout l)
 {
     MOZ_ASSERT((l.asBits >> JSVAL_TAG_SHIFT) <= JSVAL_TAG_OBJECT);
     return l.asBits >= JSVAL_LOWER_INCL_SHIFTED_TAG_OF_OBJ_OR_NULL_SET;
 }
 static inline JSObject *
 JSVAL_TO_OBJECT_IMPL(jsval_layout l)
 {
     uint64_t ptrBits = l.asBits & JSVAL_PAYLOAD_MASK;
     MOZ_ASSERT((ptrBits & 0x7) == 0);
     return (JSObject *)ptrBits;
 }
 static inline jsval_layout
 OBJECT_TO_JSVAL_IMPL(JSObject *obj)
 {
     jsval_layout l;
     uint64_t objBits = (uint64_t)obj;
     MOZ_ASSERT(uintptr_t(obj) > 0x1000 || uintptr_t(obj) == 0x42);
     MOZ_ASSERT((objBits >> JSVAL_TAG_SHIFT) == 0);
     l.asBits = objBits | JSVAL_SHIFTED_TAG_OBJECT;
     return l;
 }
 static inline bool
 JSVAL_IS_NULL_IMPL(jsval_layout l)
 {
     return l.asBits == JSVAL_SHIFTED_TAG_NULL;
 }
 static inline bool
 JSVAL_IS_GCTHING_IMPL(jsval_layout l)
 {
     return l.asBits >= JSVAL_LOWER_INCL_SHIFTED_TAG_OF_GCTHING_SET;
 }
 static inline void *
 JSVAL_TO_GCTHING_IMPL(jsval_layout l)
 {
     uint64_t ptrBits = l.asBits & JSVAL_PAYLOAD_MASK;
     MOZ_ASSERT((ptrBits & 0x7) == 0);
     return (void *)ptrBits;
 }
 static inline bool
 JSVAL_IS_TRACEABLE_IMPL(jsval_layout l)
 {
     return JSVAL_IS_GCTHING_IMPL(l) && !JSVAL_IS_NULL_IMPL(l);
 }
 static inline uint32_t
 JSVAL_TRACE_KIND_IMPL(jsval_layout l)
 {
     return (uint32_t)(bool)!(JSVAL_IS_OBJECT_IMPL(l));
 }
 static inline jsval_layout
 PRIVATE_PTR_TO_JSVAL_IMPL(void *ptr)
 {
     jsval_layout l;
     uint64_t ptrBits = (uint64_t)ptr;
     MOZ_ASSERT((ptrBits & 1) == 0);
     l.asBits = ptrBits >> 1;
     MOZ_ASSERT(JSVAL_IS_DOUBLE_IMPL(l));
     return l;
 }
 static inline void *
 JSVAL_TO_PRIVATE_PTR_IMPL(jsval_layout l)
 {
     MOZ_ASSERT((l.asBits & 0x8000000000000000LL) == 0);
     return (void *)(l.asBits << 1);
 }
 static inline bool
 JSVAL_IS_SPECIFIC_INT32_IMPL(jsval_layout l, int32_t i32)
 {
     return l.asBits == (((uint64_t)(uint32_t)i32) | JSVAL_SHIFTED_TAG_INT32);
 }
 static inline bool
 JSVAL_IS_SPECIFIC_BOOLEAN(jsval_layout l, bool b)
 {
     return l.asBits == (((uint64_t)(uint32_t)b) | JSVAL_SHIFTED_TAG_BOOLEAN);
 }
 static inline jsval_layout
 MAGIC_TO_JSVAL_IMPL(JSWhyMagic why)
 {
     jsval_layout l;
     l.asBits = ((uint64_t)(uint32_t)why) | JSVAL_SHIFTED_TAG_MAGIC;
     return l;
 }
 static inline jsval_layout
 MAGIC_UINT32_TO_JSVAL_IMPL(uint32_t payload)
 {
     jsval_layout l;
     l.asBits = ((uint64_t)payload) | JSVAL_SHIFTED_TAG_MAGIC;
     return l;
 }
 static inline bool
 JSVAL_SAME_TYPE_IMPL(jsval_layout lhs, jsval_layout rhs)
 {
     uint64_t lbits = lhs.asBits, rbits = rhs.asBits;
     return (lbits <= JSVAL_SHIFTED_TAG_MAX_DOUBLE && rbits <= JSVAL_SHIFTED_TAG_MAX_DOUBLE) ||
            (((lbits ^ rbits) & 0xFFFF800000000000LL) == 0);
 }
 static inline JSValueType
 JSVAL_EXTRACT_NON_DOUBLE_TYPE_IMPL(jsval_layout l)
 {
    uint64_t type = (l.asBits >> JSVAL_TAG_SHIFT) & 0xF;
    MOZ_ASSERT(type > JSVAL_TYPE_DOUBLE);
    return (JSValueType)type;
 }
 #endif  /* JS_BITS_PER_WORD */
 static inline jsval_layout JSVAL_TO_IMPL(JS::Value v);
 static inline JS_VALUE_CONSTEXPR JS::Value IMPL_TO_JSVAL(jsval_layout l);
 namespace JS {
 static inline JS_VALUE_CONSTEXPR JS::Value UndefinedValue();
 /**
  * Returns a generic quiet NaN value, with all payload bits set to zero.
  *
  * Among other properties, this NaN's bit pattern conforms to JS::Value's
  * bit pattern restrictions.
  */
 static MOZ_ALWAYS_INLINE double
 GenericNaN()
 {
   return mozilla::SpecificNaN<double>(0, 0x8000000000000ULL);
 }
 /* MSVC with PGO miscompiles this function. */
 #if defined(_MSC_VER)
 # pragma optimize("g", off)
 #endif
 static inline double
 CanonicalizeNaN(double d)
 {
     if (MOZ_UNLIKELY(mozilla::IsNaN(d)))
         return GenericNaN();
     return d;
 }
 #if defined(_MSC_VER)
 # pragma optimize("", on)
 #endif
 /*
  * JS::Value is the interface for a single JavaScript Engine value.  A few
  * general notes on JS::Value:
  *
  * - JS::Value has setX() and isX() members for X in
  *
  *     { Int32, Double, String, Boolean, Undefined, Null, Object, Magic }
  *
  *   JS::Value also contains toX() for each of the non-singleton types.
  *
  * - Magic is a singleton type whose payload contains either a JSWhyMagic "reason" for
  *   the magic value or a uint32_t value. By providing JSWhyMagic values when
  *   creating and checking for magic values, it is possible to assert, at
  *   runtime, that only magic values with the expected reason flow through a
  *   particular value. For example, if cx->exception has a magic value, the
  *   reason must be JS_GENERATOR_CLOSING.
  *
  * - The JS::Value operations are preferred.  The JSVAL_* operations remain for
  *   compatibility; they may be removed at some point.  These operations mostly
  *   provide similar functionality.  But there are a few key differences.  One
  *   is that JS::Value gives null a separate type. Thus
  *
  *           JSVAL_IS_OBJECT(v) === v.isObjectOrNull()
  *       !JSVAL_IS_PRIMITIVE(v) === v.isObject()
  *
  *   Also, to help prevent mistakenly boxing a nullable JSObject* as an object,
  *   Value::setObject takes a JSObject&. (Conversely, Value::toObject returns a
  *   JSObject&.)  A convenience member Value::setObjectOrNull is provided.
  *
  * - JSVAL_VOID is the same as the singleton value of the Undefined type.
  *
  * - Note that JS::Value is 8 bytes on 32 and 64-bit architectures. Thus, on
  *   32-bit user code should avoid copying jsval/JS::Value as much as possible,
  *   preferring to pass by const Value &.
  */
 class Value
 {
   public:
     /*
      * N.B. the default constructor leaves Value unitialized. Adding a default
      * constructor prevents Value from being stored in a union.
      */
 #if defined(JS_VALUE_IS_CONSTEXPR)
     Value() = default;
     Value(const Value& v) = default;
 #endif
     /*** Mutators ***/
     void setNull() {
         data.asBits = BUILD_JSVAL(JSVAL_TAG_NULL, 0).asBits;
     }
     void setUndefined() {
         data.asBits = BUILD_JSVAL(JSVAL_TAG_UNDEFINED, 0).asBits;
     }
     void setInt32(int32_t i) {
         data = INT32_TO_JSVAL_IMPL(i);
     }
     int32_t &getInt32Ref() {
         MOZ_ASSERT(isInt32());
         return data.s.payload.i32;
     }
     void setDouble(double d) {
         data = DOUBLE_TO_JSVAL_IMPL(d);
     }
     void setNaN() {
         setDouble(GenericNaN());
     }
     double &getDoubleRef() {
         MOZ_ASSERT(isDouble());
         return data.asDouble;
     }
     void setString(JSString *str) {
         MOZ_ASSERT(!IsPoisonedPtr(str));
         data = STRING_TO_JSVAL_IMPL(str);
     }
     void setObject(JSObject &obj) {
         MOZ_ASSERT(!IsPoisonedPtr(&obj));
         data = OBJECT_TO_JSVAL_IMPL(&obj);
     }
     void setBoolean(bool b) {
         data = BOOLEAN_TO_JSVAL_IMPL(b);
     }
     void setMagic(JSWhyMagic why) {
         data = MAGIC_TO_JSVAL_IMPL(why);
     }
     void setMagicUint32(uint32_t payload) {
         data = MAGIC_UINT32_TO_JSVAL_IMPL(payload);
     }
     bool setNumber(uint32_t ui) {
         if (ui > JSVAL_INT_MAX) {
             setDouble((double)ui);
             return false;
         } else {
             setInt32((int32_t)ui);
             return true;
         }
     }
     bool setNumber(double d) {
         int32_t i;
         if (mozilla::NumberIsInt32(d, &i)) {
             setInt32(i);
             return true;
         }
         setDouble(d);
         return false;
     }
     void setObjectOrNull(JSObject *arg) {
         if (arg)
             setObject(*arg);
         else
             setNull();
     }
     void swap(Value &rhs) {
         uint64_t tmp = rhs.data.asBits;
         rhs.data.asBits = data.asBits;
         data.asBits = tmp;
     }
     /*** Value type queries ***/
     bool isUndefined() const {
         return JSVAL_IS_UNDEFINED_IMPL(data);
     }
     bool isNull() const {
         return JSVAL_IS_NULL_IMPL(data);
     }
     bool isNullOrUndefined() const {
         return isNull() || isUndefined();
     }
     bool isInt32() const {
         return JSVAL_IS_INT32_IMPL(data);
     }
     bool isInt32(int32_t i32) const {
         return JSVAL_IS_SPECIFIC_INT32_IMPL(data, i32);
     }
     bool isDouble() const {
         return JSVAL_IS_DOUBLE_IMPL(data);
     }
     bool isNumber() const {
         return JSVAL_IS_NUMBER_IMPL(data);
     }
     bool isString() const {
         return JSVAL_IS_STRING_IMPL(data);
     }
     bool isObject() const {
         return JSVAL_IS_OBJECT_IMPL(data);
     }
     bool isPrimitive() const {
         return JSVAL_IS_PRIMITIVE_IMPL(data);
     }
     bool isObjectOrNull() const {
         return JSVAL_IS_OBJECT_OR_NULL_IMPL(data);
     }
     bool isGCThing() const {
         return JSVAL_IS_GCTHING_IMPL(data);
     }
     bool isBoolean() const {
         return JSVAL_IS_BOOLEAN_IMPL(data);
     }
     bool isTrue() const {
         return JSVAL_IS_SPECIFIC_BOOLEAN(data, true);
     }
     bool isFalse() const {
         return JSVAL_IS_SPECIFIC_BOOLEAN(data, false);
     }
     bool isMagic() const {
         return JSVAL_IS_MAGIC_IMPL(data);
     }
     bool isMagic(JSWhyMagic why) const {
         MOZ_ASSERT_IF(isMagic(), data.s.payload.why == why);
         return JSVAL_IS_MAGIC_IMPL(data);
     }
     bool isMarkable() const {
         return JSVAL_IS_TRACEABLE_IMPL(data);
     }
     JSGCTraceKind gcKind() const {
         MOZ_ASSERT(isMarkable());
         return JSGCTraceKind(JSVAL_TRACE_KIND_IMPL(data));
     }
     JSWhyMagic whyMagic() const {
         MOZ_ASSERT(isMagic());
         return data.s.payload.why;
     }
     uint32_t magicUint32() const {
         MOZ_ASSERT(isMagic());
         return data.s.payload.u32;
     }
     /*** Comparison ***/
     bool operator==(const Value &rhs) const {
         return data.asBits == rhs.data.asBits;
     }
     bool operator!=(const Value &rhs) const {
         return data.asBits != rhs.data.asBits;
     }
     friend inline bool SameType(const Value &lhs, const Value &rhs);
     /*** Extract the value's typed payload ***/
     int32_t toInt32() const {
         MOZ_ASSERT(isInt32());
         return JSVAL_TO_INT32_IMPL(data);
     }
     double toDouble() const {
         MOZ_ASSERT(isDouble());
         return data.asDouble;
     }
     double toNumber() const {
         MOZ_ASSERT(isNumber());
         return isDouble() ? toDouble() : double(toInt32());
     }
     JSString *toString() const {
         MOZ_ASSERT(isString());
         return JSVAL_TO_STRING_IMPL(data);
     }
     JSObject &toObject() const {
         MOZ_ASSERT(isObject());
         return *JSVAL_TO_OBJECT_IMPL(data);
     }
     JSObject *toObjectOrNull() const {
         MOZ_ASSERT(isObjectOrNull());
         return JSVAL_TO_OBJECT_IMPL(data);
     }
     void *toGCThing() const {
         MOZ_ASSERT(isGCThing());
         return JSVAL_TO_GCTHING_IMPL(data);
     }
     bool toBoolean() const {
         MOZ_ASSERT(isBoolean());
         return JSVAL_TO_BOOLEAN_IMPL(data);
     }
     uint32_t payloadAsRawUint32() const {
         MOZ_ASSERT(!isDouble());
         return data.s.payload.u32;
     }
     uint64_t asRawBits() const {
         return data.asBits;
     }
     JSValueType extractNonDoubleType() const {
         return JSVAL_EXTRACT_NON_DOUBLE_TYPE_IMPL(data);
     }
     /*
      * Private API
      *
      * Private setters/getters allow the caller to read/write arbitrary types
      * that fit in the 64-bit payload. It is the caller's responsibility, after
      * storing to a value with setPrivateX to read only using getPrivateX.
      * Privates values are given a type which ensures they are not marked.
      */
     void setPrivate(void *ptr) {
         data = PRIVATE_PTR_TO_JSVAL_IMPL(ptr);
     }
     void *toPrivate() const {
         MOZ_ASSERT(JSVAL_IS_DOUBLE_IMPL(data));
         return JSVAL_TO_PRIVATE_PTR_IMPL(data);
     }
     void setPrivateUint32(uint32_t ui) {
         MOZ_ASSERT(uint32_t(int32_t(ui)) == ui);
         setInt32(int32_t(ui));
     }
     uint32_t toPrivateUint32() const {
         return uint32_t(toInt32());
     }
     /*
      * An unmarked value is just a void* cast as a Value. Thus, the Value is
      * not safe for GC and must not be marked. This API avoids raw casts
      * and the ensuing strict-aliasing warnings.
      */
     void setUnmarkedPtr(void *ptr) {
         data.asPtr = ptr;
     }
     void *toUnmarkedPtr() const {
         return data.asPtr;
     }
     const size_t *payloadWord() const {
 #if JS_BITS_PER_WORD == 32
         return &data.s.payload.word;
 #elif JS_BITS_PER_WORD == 64
         return &data.asWord;
 #endif
     }
     const uintptr_t *payloadUIntPtr() const {
 #if JS_BITS_PER_WORD == 32
         return &data.s.payload.uintptr;
 #elif JS_BITS_PER_WORD == 64
         return &data.asUIntPtr;
 #endif
     }
 #if !defined(_MSC_VER) && !defined(__sparc)
   // Value must be POD so that MSVC will pass it by value and not in memory
   // (bug 689101); the same is true for SPARC as well (bug 737344).  More
   // precisely, we don't want Value return values compiled as out params.
   private:
 #endif
     jsval_layout data;
   private:
 #if defined(JS_VALUE_IS_CONSTEXPR)
     JS_VALUE_CONSTEXPR Value(jsval_layout layout) : data(layout) {}
 #endif
     void staticAssertions() {
         JS_STATIC_ASSERT(sizeof(JSValueType) == 1);
         JS_STATIC_ASSERT(sizeof(JSValueTag) == 4);
         JS_STATIC_ASSERT(sizeof(JSWhyMagic) <= 4);
         JS_STATIC_ASSERT(sizeof(Value) == 8);
     }
     friend jsval_layout (::JSVAL_TO_IMPL)(Value);
     friend Value JS_VALUE_CONSTEXPR (::IMPL_TO_JSVAL)(jsval_layout l);
     friend Value JS_VALUE_CONSTEXPR (JS::UndefinedValue)();
 };
 inline bool
 IsPoisonedValue(const Value &v)
 {
     if (v.isString())
         return IsPoisonedPtr(v.toString());
     if (v.isObject())
         return IsPoisonedPtr(&v.toObject());
     return false;
 }
 inline bool
 IsOptimizedPlaceholderMagicValue(const Value &v)
 {
     if (v.isMagic()) {
         MOZ_ASSERT(v.whyMagic() == JS_OPTIMIZED_ARGUMENTS || v.whyMagic() == JS_OPTIMIZED_OUT);
         return true;
     }
     return false;
 }
 /************************************************************************/
 static inline Value
 NullValue()
 {
     Value v;
     v.setNull();
     return v;
 }
 static inline JS_VALUE_CONSTEXPR Value
 UndefinedValue()
 {
 #if defined(JS_VALUE_IS_CONSTEXPR)
     return Value(BUILD_JSVAL(JSVAL_TAG_UNDEFINED, 0));
 #else
     JS::Value v;
     v.setUndefined();
     return v;
 #endif
 }
 static inline Value
 Int32Value(int32_t i32)
 {
     Value v;
     v.setInt32(i32);
     return v;
 }
 static inline Value
 DoubleValue(double dbl)
 {
     Value v;
     v.setDouble(dbl);
     return v;
 }
 static inline Value
 DoubleNaNValue()
 {
     Value v;
     v.setNaN();
     return v;
 }
 static inline Value
 Float32Value(float f)
 {
     Value v;
     v.setDouble(f);
     return v;
 }
 static inline Value
 StringValue(JSString *str)
 {
     Value v;
     v.setString(str);
     return v;
 }
 static inline Value
 BooleanValue(bool boo)
 {
     Value v;
     v.setBoolean(boo);
     return v;
 }
 static inline Value
 TrueValue()
 {
     Value v;
     v.setBoolean(true);
     return v;
 }
 static inline Value
 FalseValue()
 {
     Value v;
     v.setBoolean(false);
     return v;
 }
 static inline Value
 ObjectValue(JSObject &obj)
 {
     Value v;
     v.setObject(obj);
     return v;
 }
 static inline Value
 ObjectValueCrashOnTouch()
 {
     Value v;
     v.setObject(*reinterpret_cast<JSObject *>(0x42));
     return v;
 }
 static inline Value
 MagicValue(JSWhyMagic why)
 {
     Value v;
     v.setMagic(why);
     return v;
 }
 static inline Value
 MagicValueUint32(uint32_t payload)
 {
     Value v;
     v.setMagicUint32(payload);
     return v;
 }
 static inline Value
 NumberValue(float f)
 {
     Value v;
     v.setNumber(f);
     return v;
 }
 static inline Value
 NumberValue(double dbl)
 {
     Value v;
     v.setNumber(dbl);
     return v;
 }
 static inline Value
 NumberValue(int8_t i)
 {
     return Int32Value(i);
 }
 static inline Value
 NumberValue(uint8_t i)
 {
     return Int32Value(i);
 }
 static inline Value
 NumberValue(int16_t i)
 {
     return Int32Value(i);
 }
 static inline Value
 NumberValue(uint16_t i)
 {
     return Int32Value(i);
 }
 static inline Value
 NumberValue(int32_t i)
 {
     return Int32Value(i);
 }
 static inline Value
 NumberValue(uint32_t i)
 {
     Value v;
     v.setNumber(i);
     return v;
 }
 namespace detail {
 template <bool Signed>
 class MakeNumberValue
 {
   public:
     template<typename T>
     static inline Value create(const T t)
     {
         Value v;
         if (JSVAL_INT_MIN <= t && t <= JSVAL_INT_MAX)
             v.setInt32(int32_t(t));
         else
             v.setDouble(double(t));
         return v;
     }
 };
 template <>
 class MakeNumberValue<false>
 {
   public:
     template<typename T>
     static inline Value create(const T t)
     {
         Value v;
         if (t <= JSVAL_INT_MAX)
             v.setInt32(int32_t(t));
         else
             v.setDouble(double(t));
         return v;
     }
 };
 } // namespace detail
 template <typename T>
 static inline Value
 NumberValue(const T t)
 {
     MOZ_ASSERT(T(double(t)) == t, "value creation would be lossy");
     return detail::MakeNumberValue<std::numeric_limits<T>::is_signed>::create(t);
 }
 static inline Value
 ObjectOrNullValue(JSObject *obj)
 {
     Value v;
     v.setObjectOrNull(obj);
     return v;
 }
 static inline Value
 PrivateValue(void *ptr)
 {
     Value v;
     v.setPrivate(ptr);
     return v;
 }
 static inline Value
 PrivateUint32Value(uint32_t ui)
 {
     Value v;
     v.setPrivateUint32(ui);
     return v;
 }
 inline bool
 SameType(const Value &lhs, const Value &rhs)
 {
     return JSVAL_SAME_TYPE_IMPL(lhs.data, rhs.data);
 }
 } // namespace JS
 /************************************************************************/
 #ifdef JSGC_GENERATIONAL
 namespace JS {
 JS_PUBLIC_API(void) HeapValuePostBarrier(Value *valuep);
 JS_PUBLIC_API(void) HeapValueRelocate(Value *valuep);
 }
 #endif
 namespace js {
 template <> struct GCMethods<const JS::Value>
 {
     static JS::Value initial() { return JS::UndefinedValue(); }
     static ThingRootKind kind() { return THING_ROOT_VALUE; }
     static bool poisoned(const JS::Value &v) { return JS::IsPoisonedValue(v); }
 };
 template <> struct GCMethods<JS::Value>
 {
     static JS::Value initial() { return JS::UndefinedValue(); }
     static ThingRootKind kind() { return THING_ROOT_VALUE; }
     static bool poisoned(const JS::Value &v) { return JS::IsPoisonedValue(v); }
     static bool needsPostBarrier(const JS::Value &v) { return v.isMarkable(); }
 #ifdef JSGC_GENERATIONAL
     static void postBarrier(JS::Value *v) { JS::HeapValuePostBarrier(v); }
     static void relocate(JS::Value *v) { JS::HeapValueRelocate(v); }
 #endif
 };
 template <class Outer> class MutableValueOperations;
 /*
  * A class designed for CRTP use in implementing the non-mutating parts of the
  * Value interface in Value-like classes.  Outer must be a class inheriting
  * ValueOperations<Outer> with a visible extract() method returning the
  * const Value* abstracted by Outer.
  */
 template <class Outer>
 class ValueOperations
 {
     friend class MutableValueOperations<Outer>;
     const JS::Value * value() const { return static_cast<const Outer*>(this)->extract(); }
   public:
     bool isUndefined() const { return value()->isUndefined(); }
     bool isNull() const { return value()->isNull(); }
     bool isBoolean() const { return value()->isBoolean(); }
     bool isTrue() const { return value()->isTrue(); }
     bool isFalse() const { return value()->isFalse(); }
     bool isNumber() const { return value()->isNumber(); }
     bool isInt32() const { return value()->isInt32(); }
     bool isDouble() const { return value()->isDouble(); }
     bool isString() const { return value()->isString(); }
     bool isObject() const { return value()->isObject(); }
     bool isMagic() const { return value()->isMagic(); }
     bool isMagic(JSWhyMagic why) const { return value()->isMagic(why); }
     bool isMarkable() const { return value()->isMarkable(); }
     bool isPrimitive() const { return value()->isPrimitive(); }
     bool isGCThing() const { return value()->isGCThing(); }
     bool isNullOrUndefined() const { return value()->isNullOrUndefined(); }
     bool isObjectOrNull() const { return value()->isObjectOrNull(); }
     bool toBoolean() const { return value()->toBoolean(); }
     double toNumber() const { return value()->toNumber(); }
     int32_t toInt32() const { return value()->toInt32(); }
     double toDouble() const { return value()->toDouble(); }
     JSString *toString() const { return value()->toString(); }
     JSObject &toObject() const { return value()->toObject(); }
     JSObject *toObjectOrNull() const { return value()->toObjectOrNull(); }
     void *toGCThing() const { return value()->toGCThing(); }
     JSValueType extractNonDoubleType() const { return value()->extractNonDoubleType(); }
     uint32_t toPrivateUint32() const { return value()->toPrivateUint32(); }
     JSWhyMagic whyMagic() const { return value()->whyMagic(); }
     uint32_t magicUint32() const { return value()->magicUint32(); }
 };
 /*
  * A class designed for CRTP use in implementing all the mutating parts of the
  * Value interface in Value-like classes.  Outer must be a class inheriting
  * MutableValueOperations<Outer> with visible extractMutable() and extract()
  * methods returning the const Value* and Value* abstracted by Outer.
  */
 template <class Outer>
 class MutableValueOperations : public ValueOperations<Outer>
 {
     JS::Value * value() { return static_cast<Outer*>(this)->extractMutable(); }
   public:
     void setNull() { value()->setNull(); }
     void setUndefined() { value()->setUndefined(); }
     void setInt32(int32_t i) { value()->setInt32(i); }
     void setDouble(double d) { value()->setDouble(d); }
     void setNaN() { setDouble(JS::GenericNaN()); }
     void setBoolean(bool b) { value()->setBoolean(b); }
     void setMagic(JSWhyMagic why) { value()->setMagic(why); }
     bool setNumber(uint32_t ui) { return value()->setNumber(ui); }
     bool setNumber(double d) { return value()->setNumber(d); }
     void setString(JSString *str) { this->value()->setString(str); }
     void setObject(JSObject &obj) { this->value()->setObject(obj); }
     void setObjectOrNull(JSObject *arg) { this->value()->setObjectOrNull(arg); }
 };
 /*
  * Augment the generic Heap<T> interface when T = Value with
  * type-querying, value-extracting, and mutating operations.
  */
 template <>
 class HeapBase<JS::Value> : public ValueOperations<JS::Heap<JS::Value> >
 {
     typedef JS::Heap<JS::Value> Outer;
     friend class ValueOperations<Outer>;
     const JS::Value * extract() const { return static_cast<const Outer*>(this)->address(); }
     void setBarriered(const JS::Value &v) {
         static_cast<JS::Heap<JS::Value> *>(this)->set(v);
     }
   public:
     void setNull() { setBarriered(JS::NullValue()); }
     void setUndefined() { setBarriered(JS::UndefinedValue()); }
     void setInt32(int32_t i) { setBarriered(JS::Int32Value(i)); }
     void setDouble(double d) { setBarriered(JS::DoubleValue(d)); }
     void setNaN() { setDouble(JS::GenericNaN()); }
     void setBoolean(bool b) { setBarriered(JS::BooleanValue(b)); }
     void setMagic(JSWhyMagic why) { setBarriered(JS::MagicValue(why)); }
     void setString(JSString *str) { setBarriered(JS::StringValue(str)); }
     void setObject(JSObject &obj) { setBarriered(JS::ObjectValue(obj)); }
     bool setNumber(uint32_t ui) {
         if (ui > JSVAL_INT_MAX) {
             setDouble((double)ui);
             return false;
         } else {
             setInt32((int32_t)ui);
             return true;
         }
     }
     bool setNumber(double d) {
         int32_t i;
         if (mozilla::NumberIsInt32(d, &i)) {
             setInt32(i);
             return true;
         }
         setDouble(d);
         return false;
     }
     void setObjectOrNull(JSObject *arg) {
         if (arg)
             setObject(*arg);
         else
             setNull();
     }
 };
 /*
  * Augment the generic Handle<T> interface when T = Value with type-querying
  * and value-extracting operations.
  */
 template <>
 class HandleBase<JS::Value> : public ValueOperations<JS::Handle<JS::Value> >
 {
     friend class ValueOperations<JS::Handle<JS::Value> >;
     const JS::Value * extract() const {
         return static_cast<const JS::Handle<JS::Value>*>(this)->address();
     }
 };
 /*
  * Augment the generic MutableHandle<T> interface when T = Value with
  * type-querying, value-extracting, and mutating operations.
  */
 template <>
 class MutableHandleBase<JS::Value> : public MutableValueOperations<JS::MutableHandle<JS::Value> >
 {
     friend class ValueOperations<JS::MutableHandle<JS::Value> >;
     const JS::Value * extract() const {
         return static_cast<const JS::MutableHandle<JS::Value>*>(this)->address();
     }
     friend class MutableValueOperations<JS::MutableHandle<JS::Value> >;
     JS::Value * extractMutable() {
         return static_cast<JS::MutableHandle<JS::Value>*>(this)->address();
     }
 };
 /*
  * Augment the generic Rooted<T> interface when T = Value with type-querying,
  * value-extracting, and mutating operations.
  */
 template <>
 class RootedBase<JS::Value> : public MutableValueOperations<JS::Rooted<JS::Value> >
 {
     friend class ValueOperations<JS::Rooted<JS::Value> >;
     const JS::Value * extract() const {
         return static_cast<const JS::Rooted<JS::Value>*>(this)->address();
     }
     friend class MutableValueOperations<JS::Rooted<JS::Value> >;
     JS::Value * extractMutable() {
         return static_cast<JS::Rooted<JS::Value>*>(this)->address();
     }
 };
 } // namespace js
 inline jsval_layout
 JSVAL_TO_IMPL(JS::Value v)
 {
     return v.data;
 }
 inline JS_VALUE_CONSTEXPR JS::Value
 IMPL_TO_JSVAL(jsval_layout l)
 {
 #if defined(JS_VALUE_IS_CONSTEXPR)
     return JS::Value(l);
 #else
     JS::Value v;
     v.data = l;
     return v;
 #endif
 }
 namespace JS {
 #ifndef __GNUC__
 /*
  * The default assignment operator for |struct C| has the signature:
  *
  *   C& C::operator=(const C&)
  *
  * And in particular requires implicit conversion of |this| to type |C| for the
  * return value. But |volatile C| cannot thus be converted to |C|, so just
  * doing |sink = hold| as in the non-specialized version would fail to compile.
  * Do the assignment on asBits instead, since I don't think we want to give
  * jsval_layout an assignment operator returning |volatile jsval_layout|.
  */
 template<>
 inline Anchor<Value>::~Anchor()
 {
     volatile uint64_t bits;
     bits = JSVAL_TO_IMPL(hold).asBits;
 }
 #endif
 #ifdef JS_DEBUG
 namespace detail {
 struct ValueAlignmentTester { char c; JS::Value v; };
 static_assert(sizeof(ValueAlignmentTester) == 16,
               "JS::Value must be 16-byte-aligned");
 struct LayoutAlignmentTester { char c; jsval_layout l; };
 static_assert(sizeof(LayoutAlignmentTester) == 16,
               "jsval_layout must be 16-byte-aligned");
 } // namespace detail
 #endif /* JS_DEBUG */
 } // namespace JS
 /*
  * JS::Value and jsval are the same type; jsval is the old name, kept around
  * for backwards compatibility along with all the JSVAL_* operations below.
  * jsval_layout is an implementation detail and should not be used externally.
  */
 typedef JS::Value jsval;
 static_assert(sizeof(jsval_layout) == sizeof(JS::Value),
               "jsval_layout and JS::Value must have identical layouts");
 /************************************************************************/
 static inline bool
 JSVAL_IS_NULL(jsval v)
 {
     return JSVAL_IS_NULL_IMPL(JSVAL_TO_IMPL(v));
 }
 static inline bool
 JSVAL_IS_VOID(jsval v)
 {
     return JSVAL_IS_UNDEFINED_IMPL(JSVAL_TO_IMPL(v));
 }
 static inline bool
 JSVAL_IS_INT(jsval v)
 {
     return JSVAL_IS_INT32_IMPL(JSVAL_TO_IMPL(v));
 }
 static inline int32_t
 JSVAL_TO_INT(jsval v)
 {
     MOZ_ASSERT(JSVAL_IS_INT(v));
     return JSVAL_TO_INT32_IMPL(JSVAL_TO_IMPL(v));
 }
 static inline JS_VALUE_CONSTEXPR jsval
 INT_TO_JSVAL(int32_t i)
 {
     return IMPL_TO_JSVAL(INT32_TO_JSVAL_IMPL(i));
 }
 static inline bool
 JSVAL_IS_DOUBLE(jsval v)
 {
     return JSVAL_IS_DOUBLE_IMPL(JSVAL_TO_IMPL(v));
 }
 static inline double
 JSVAL_TO_DOUBLE(jsval v)
 {
     jsval_layout l;
     MOZ_ASSERT(JSVAL_IS_DOUBLE(v));
     l = JSVAL_TO_IMPL(v);
     return l.asDouble;
 }
 static inline JS_VALUE_CONSTEXPR jsval
 DOUBLE_TO_JSVAL(double d)
 {
     /*
      * This is a manually inlined version of:
      *    d = JS_CANONICALIZE_NAN(d);
      *    return IMPL_TO_JSVAL(DOUBLE_TO_JSVAL_IMPL(d));
      * because GCC from XCode 3.1.4 miscompiles the above code.
      */
 #if defined(JS_VALUE_IS_CONSTEXPR)
     return IMPL_TO_JSVAL(MOZ_UNLIKELY(d != d)
                          ? (jsval_layout) { .asBits = 0x7FF8000000000000LL }
                          : (jsval_layout) { .asDouble = d });
 #else
     jsval_layout l;
     if (MOZ_UNLIKELY(d != d))
         l.asBits = 0x7FF8000000000000LL;
     else
         l.asDouble = d;
     return IMPL_TO_JSVAL(l);
 #endif
 }
 static inline JS_VALUE_CONSTEXPR jsval
 UINT_TO_JSVAL(uint32_t i)
 {
     return (i <= JSVAL_INT_MAX
             ? INT_TO_JSVAL((int32_t)i)
             : DOUBLE_TO_JSVAL((double)i));
 }
 static inline bool
 JSVAL_IS_NUMBER(jsval v)
 {
     return JSVAL_IS_NUMBER_IMPL(JSVAL_TO_IMPL(v));
 }
 static inline bool
 JSVAL_IS_STRING(jsval v)
 {
     return JSVAL_IS_STRING_IMPL(JSVAL_TO_IMPL(v));
 }
 static inline JSString *
 JSVAL_TO_STRING(jsval v)
 {
     MOZ_ASSERT(JSVAL_IS_STRING(v));
     return JSVAL_TO_STRING_IMPL(JSVAL_TO_IMPL(v));
 }
 static inline jsval
 STRING_TO_JSVAL(JSString *str)
 {
     return IMPL_TO_JSVAL(STRING_TO_JSVAL_IMPL(str));
 }
 static inline JSObject *
 JSVAL_TO_OBJECT(jsval v)
 {
     MOZ_ASSERT(JSVAL_IS_OBJECT_OR_NULL_IMPL(JSVAL_TO_IMPL(v)));
     return JSVAL_TO_OBJECT_IMPL(JSVAL_TO_IMPL(v));
 }
 static inline jsval
 OBJECT_TO_JSVAL(JSObject *obj)
 {
     if (obj)
         return IMPL_TO_JSVAL(OBJECT_TO_JSVAL_IMPL(obj));
     return IMPL_TO_JSVAL(BUILD_JSVAL(JSVAL_TAG_NULL, 0));
 }
 static inline bool
 JSVAL_IS_BOOLEAN(jsval v)
 {
     return JSVAL_IS_BOOLEAN_IMPL(JSVAL_TO_IMPL(v));
 }
 static inline bool
 JSVAL_TO_BOOLEAN(jsval v)
 {
     MOZ_ASSERT(JSVAL_IS_BOOLEAN(v));
     return JSVAL_TO_BOOLEAN_IMPL(JSVAL_TO_IMPL(v));
 }
 static inline jsval
 BOOLEAN_TO_JSVAL(bool b)
 {
     return IMPL_TO_JSVAL(BOOLEAN_TO_JSVAL_IMPL(b));
 }
 static inline bool
 JSVAL_IS_PRIMITIVE(jsval v)
 {
     return JSVAL_IS_PRIMITIVE_IMPL(JSVAL_TO_IMPL(v));
 }
 static inline bool
 JSVAL_IS_GCTHING(jsval v)
 {
     return JSVAL_IS_GCTHING_IMPL(JSVAL_TO_IMPL(v));
 }
 static inline void *
 JSVAL_TO_GCTHING(jsval v)
 {
     MOZ_ASSERT(JSVAL_IS_GCTHING(v));
     return JSVAL_TO_GCTHING_IMPL(JSVAL_TO_IMPL(v));
 }
 /* To be GC-safe, privates are tagged as doubles. */
 static inline jsval
 PRIVATE_TO_JSVAL(void *ptr)
 {
     return IMPL_TO_JSVAL(PRIVATE_PTR_TO_JSVAL_IMPL(ptr));
 }
 static inline void *
 JSVAL_TO_PRIVATE(jsval v)
 {
     MOZ_ASSERT(JSVAL_IS_DOUBLE(v));
     return JSVAL_TO_PRIVATE_PTR_IMPL(JSVAL_TO_IMPL(v));
 }
 // JS constants. For efficiency, prefer predicates (e.g. v.isNull()) and
 // constructing values from scratch (e.g. Int32Value(0)).  These constants are
 // stored in memory and initialized at startup, so testing against them and
 // using them requires memory loads and will be correspondingly slow.
 extern JS_PUBLIC_DATA(const jsval) JSVAL_NULL;
 extern JS_PUBLIC_DATA(const jsval) JSVAL_ZERO;
 extern JS_PUBLIC_DATA(const jsval) JSVAL_ONE;
 extern JS_PUBLIC_DATA(const jsval) JSVAL_FALSE;
 extern JS_PUBLIC_DATA(const jsval) JSVAL_TRUE;
 extern JS_PUBLIC_DATA(const jsval) JSVAL_VOID;
 namespace JS {
 extern JS_PUBLIC_DATA(const HandleValue) NullHandleValue;
 extern JS_PUBLIC_DATA(const HandleValue) UndefinedHandleValue;
 }
 #undef JS_VALUE_IS_CONSTEXPR
 #undef JS_RETURN_LAYOUT_FROM_BITS
 #endif /* js_Value_h */

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js/public/Value.h