/*
Format of a non-union-type Lisp Object
- For the USE_MINIMAL_TAGBITS implementation:
-
3 2 1 0
bit 10987654321098765432109876543210
--------------------------------
--------------------------------
VVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVT
- For the non-USE_MINIMAL_TAGBITS implementation:
-
- 3 2 1 0
- bit 10987654321098765432109876543210
- --------------------------------
- TTTMVVVVVVVVVVVVVVVVVVVVVVVVVVVV
-
- V = value bits
- T = type bits
- M = mark bits
-
For integral Lisp types, i.e. integers and characters, the value
bits are the Lisp object.
- The object is obtained by masking off the type and mark
- bits. In the USE_MINIMAL_TAGBITS implementation, bit 1 is
- used as a value bit by splitting the Lisp integer type into
- two subtypes, Lisp_Type_Int_Even and Lisp_Type_Int_Odd. By
+ The object is obtained by masking off the type and mark bits.
+ Bit 1 is used as a value bit by splitting the Lisp integer type
+ into two subtypes, Lisp_Type_Int_Even and Lisp_Type_Int_Odd. By
this trickery we get 31 bits for integers instead of 30.
- In the non-USE_MINIMAL_TAGBITS world, Lisp integers are 28 bits,
- or more properly (BITS_PER_EMACS_INT - GCTYPEBITS - 1) bits.
-
For non-integral types, the value bits of a Lisp_Object contain
a pointer to a structure containing the object. The pointer is
obtained by masking off the type and mark bits.
- In the USE_MINIMAL_TAGBITS implementation, all
- pointer-based types are coalesced under a single type called
+ All pointer-based types are coalesced under a single type called
Lisp_Type_Record. The type bits for this type are required
by the implementation to be 00, just like the least
significant bits of word-aligned struct pointers on 32-bit
hardware. Because of this, Lisp_Object pointers don't have
to be masked and are full-sized.
- In the non-USE_MINIMAL_TAGBITS implementation, the type and
- mark bits must be masked off and pointers are limited to 28
- bits (really BITS_PER_EMACS_INT - GCTYPEBITS - 1 bits).
-
- There are no mark bits in the USE_MINIMAL_TAGBITS implementation.
+ There are no mark bits.
Integers and characters don't need to be marked. All other types
are lrecord-based, which means they get marked by incrementing
their ->implementation pointer.
- In the non-USE_MINIMAL_TAGBITS implementation, the markbit is stored
- in the Lisp_Object itself. It is stored in the middle so that the
- type bits can be obtained by simply shifting them.
-
- Outside of garbage collection, all mark bits are always zero.
-
Here is a brief description of the following macros:
- XMARKBIT Extract the mark bit (non-USE_MINIMAL_TAGBITS)
- XMARK Set the mark bit of this Lisp_Object (non-USE_MINIMAL_TAGBITS)
- XUNMARK Clear the mark bit of this Lisp_Object (non-USE_MINIMAL_TAGBITS)
XTYPE The type bits of a Lisp_Object
XPNTRVAL The value bits of a Lisp_Object storing a pointer
XCHARVAL The value bits of a Lisp_Object storing a Emchar
INTP Non-zero if this Lisp_Object an integer?
Qzero Lisp Integer 0
EQ Non-zero if two Lisp_Objects are identical
- GC_EQ Version of EQ used during garbage collection
-*/
+ GC_EQ Version of EQ used during garbage collection */
typedef EMACS_INT Lisp_Object;
-#ifdef USE_MINIMAL_TAGBITS
-
-# define Lisp_Type_Int_Bit (Lisp_Type_Int_Even & Lisp_Type_Int_Odd)
-# define XUNMARK(x) DO_NOTHING
-# define make_obj(vartype, x) ((Lisp_Object) (x))
-# define make_int(x) ((Lisp_Object) (((x) << INT_GCBITS) | Lisp_Type_Int_Bit))
-# define make_char(x) ((Lisp_Object) (((x) << GCBITS) | Lisp_Type_Char))
-# define VALMASK (((1UL << VALBITS) - 1UL) << GCTYPEBITS)
-# define XTYPE(x) ((enum Lisp_Type) (((EMACS_UINT)(x)) & ~VALMASK))
-# define XPNTRVAL(x) (x) /* This depends on Lisp_Type_Record == 0 */
-# define XCHARVAL(x) ((x) >> GCBITS)
-# define GC_EQ(x,y) EQ (x,y)
-# define XREALINT(x) ((x) >> INT_GCBITS)
-# define XUINT(x) ((EMACS_UINT)(x) >> INT_GCBITS)
-# define INTP(x) ((EMACS_UINT)(x) & Lisp_Type_Int_Bit)
-
-#else /* !USE_MINIMAL_TAGBITS */
-
-# define MARKBIT (1UL << VALBITS)
-# define XMARKBIT(x) (((x) & MARKBIT) != 0)
-# define XMARK(x) ((void) ((x) |= MARKBIT))
-# define XUNMARK(x) ((void) ((x) &= ~MARKBIT))
-# define make_obj(vartype, value) \
- ((Lisp_Object) (((EMACS_UINT) (vartype) << (VALBITS + GCMARKBITS)) \
- + ((EMACS_UINT) (value) & VALMASK)))
-# define make_int(value) make_obj (Lisp_Type_Int, value)
-# define make_char(value) make_obj (Lisp_Type_Char, value)
-# define VALMASK ((1UL << VALBITS) - 1UL)
-# define XTYPE(x) ((enum Lisp_Type) (((EMACS_UINT)(x)) >> (VALBITS + GCMARKBITS)))
-# define XPNTRVAL(x) ((x) & VALMASK)
-# define XCHARVAL(x) XPNTRVAL(x)
-# define GC_EQ(x,y) (((x) & ~MARKBIT) == ((y) & ~MARKBIT))
-# define XREALINT(x) (((x) << INT_GCBITS) >> INT_GCBITS)
-# define XUINT(x) ((EMACS_UINT) ((x) & VALMASK))
-# define INTP(x) (XTYPE (x) == Lisp_Type_Int)
-
-#endif /* !USE_MINIMAL_TAGBITS */
+#define Lisp_Type_Int_Bit (Lisp_Type_Int_Even & Lisp_Type_Int_Odd)
+#define make_obj(vartype, x) ((Lisp_Object) (x))
+#define make_int(x) ((Lisp_Object) (((x) << INT_GCBITS) | Lisp_Type_Int_Bit))
+#define make_char(x) ((Lisp_Object) (((x) << GCBITS) | Lisp_Type_Char))
+#define VALMASK (((1UL << VALBITS) - 1UL) << GCTYPEBITS)
+#define XTYPE(x) ((enum Lisp_Type) (((EMACS_UINT)(x)) & ~VALMASK))
+#define XPNTRVAL(x) (x) /* This depends on Lisp_Type_Record == 0 */
+#define XCHARVAL(x) ((x) >> GCBITS)
+#define GC_EQ(x,y) EQ (x,y)
+#define XREALINT(x) ((x) >> INT_GCBITS)
+#define XUINT(x) ((EMACS_UINT)(x) >> INT_GCBITS)
+#define INTP(x) ((EMACS_UINT)(x) & Lisp_Type_Int_Bit)
#define Qzero make_int (0)
#define Qnull_pointer ((Lisp_Object) 0)
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