/*
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.
- 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. 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
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.
- All pointer-based types are coalesced under a single type called
+ In the USE_MINIMAL_TAGBITS implementation, 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.
- There are no mark bits.
+ 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.
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
XUINT The value bits of a Lisp_Object storing an integer, unsigned
INTP Non-zero if this Lisp_Object an integer?
Qzero Lisp Integer 0
- EQ Non-zero if two Lisp_Objects are identical */
-
+ EQ Non-zero if two Lisp_Objects are identical
+ GC_EQ Version of EQ used during garbage collection
+*/
typedef EMACS_INT Lisp_Object;
-#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 XREALINT(x) ((x) >> INT_GCBITS)
-#define XUINT(x) ((EMACS_UINT)(x) >> INT_GCBITS)
-#define INTP(x) ((EMACS_UINT)(x) & Lisp_Type_Int_Bit)
-#define INT_PLUS(x,y) ((x)+(y)-Lisp_Type_Int_Bit)
-#define INT_MINUS(x,y) ((x)-(y)+Lisp_Type_Int_Bit)
-#define INT_PLUS1(x) INT_PLUS (x, make_int (1))
-#define INT_MINUS1(x) INT_MINUS (x, make_int (1))
-
-#define Qzero make_int (0)
-#define Qnull_pointer ((Lisp_Object) 0)
+#ifdef USE_MINIMAL_TAGBITS
+
+# define XUNMARK(x) DO_NOTHING
+# define make_obj(vartype, x) ((Lisp_Object) (x))
+# define make_int(x) ((Lisp_Object) (((x) << INT_GCBITS) + 1))
+# 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) & 1)
+# define Qzero ((Lisp_Object) 1UL)
+
+#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)
+# define Qzero ((Lisp_Object) Lisp_Type_Int)
+
+#endif /* !USE_MINIMAL_TAGBITS */
+
+#define Qnull_pointer 0
+#define XGCTYPE(x) XTYPE(x)
#define EQ(x,y) ((x) == (y))
#define XSETINT(var, value) ((void) ((var) = make_int (value)))
#define XSETCHAR(var, value) ((void) ((var) = make_char (value)))
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