boxing_nan.h: implement Favor pointer NaN Boxing.
Favor pointer means encode NaN boxed values to keep pointer values
unmodified, to reduce the cost of far frequent pointer value retrievals.
MODIFY
include/mruby/boxing_nan.h
include/mruby/boxing_nan.h
#define MRB_FIXNUM_MAX INT32_MAX
enum mrb_nanbox_tt_inline {
- MRB_NANBOX_TT_OBJECT = 1,
- MRB_NANBOX_TT_INTEGER,
- MRB_NANBOX_TT_SYMBOL,
- MRB_NANBOX_TT_POINTER,
- MRB_NANBOX_TT_MISC,
+ MRB_NANBOX_TT_POINTER = 0,
+ MRB_NANBOX_TT_INTEGER = 1,
+ MRB_NANBOX_TT_SYMBOL = 2,
+ MRB_NANBOX_TT_MISC = 3,
};
/* value representation by nan-boxing:
- * float : FFFFFFFFFFFFFFFF FFFFFFFFFFFFFFFF FFFFFFFFFFFFFFFF FFFFFFFFFFFFFFFF
- * object: 1111111111110001 PPPPPPPPPPPPPPPP PPPPPPPPPPPPPPPP PPPPPPPPPPPPPPPP
- * int : 1111111111110010 0000000000000000 IIIIIIIIIIIIIIII IIIIIIIIIIIIIIII
- * sym : 1111111111110011 0000000000000000 SSSSSSSSSSSSSSSS SSSSSSSSSSSSSSSS
- * ptr : 1111111111110100 0000000000000000 SSSSSSSSSSSSSSSS SSSSSSSSSSSSSSSS
- * misc : 1111111111110101 0000000000000000 0000000000000000 TTTTTT000000MMMM
+ * float : SEEEEEEE EEEEFFFF FFFFFFFF FFFFFFFF FFFFFFFF FFFFFFFF FFFFFFFF FFFFFFFF
+ * +/-inf: S1111111 11110000 00000000 00000000 00000000 00000000 00000000 00000000
+ * nan : 01111111 11111000 00000000 00000000 00000000 00000000 00000000 00000000
+ * int : 01111111 11111001 00000000 00000000 IIIIIIII IIIIIIII IIIIIIII IIIIIIII
+ * sym : 01111111 11111110 00000000 00000000 SSSSSSSS SSSSSSSS SSSSSSSS SSSSSSSS
+ * misc : 01111111 11111111 00000000 00000000 00000000 00000000 00TTTTTT 0000MMMM
+ * object: 01111111 11111100 PPPPPPPP PPPPPPPP PPPPPPPP PPPPPPPP PPPPPPPP PPPPPP00
+ * ptr : 01111111 11111100 PPPPPPPP PPPPPPPP PPPPPPPP PPPPPPPP PPPPPPPP PPPPPP01
+ * Stored as O = R + 0x8004000000000000, retrieved as R = O - 0x8004000000000000.
+ * This makes pointers have all zeros in the top 32 bits.
+ * Small-ints and strs have 1 as LSB to make sure they don't look like pointers
+ * to the garbage collector.
*/
typedef struct mrb_value {
uint64_t u;
} mrb_value;
-union mrb_value_ {
- mrb_float f;
- uint64_t u;
-#ifdef MRB_64BIT
- void *p;
-# define NANBOX_IMMEDIATE_VALUE uint32_t i
-#else
-# define NANBOX_IMMEDIATE_VALUE union { uint32_t i; void *p; }
-#endif
- struct {
- MRB_ENDIAN_LOHI(
- uint32_t ttt;
- ,NANBOX_IMMEDIATE_VALUE;
- )
- };
- mrb_value value;
-};
-
-mrb_static_assert(sizeof(mrb_value) == sizeof(union mrb_value_));
-
static inline mrb_float
-mrb_float(mrb_value v)
+mrb_nan_boxing_value_float(mrb_value v)
{
union {
mrb_float f;
uint64_t u;
} x;
- x.u = v.u;
+ x.u = v.u - 0x8004000000000000;
return x.f;
}
-#define SET_FLOAT_VALUE(mrb,r,v) do { \
+#define SET_FLOAT_VALUE(mrb,r,f) do { \
union { \
mrb_float f; \
uint64_t u; \
} float_uint_union; \
- if ((v) != (v)) { /* NaN */ \
+ if ((f) != (f)) { /* NaN */ \
float_uint_union.u = 0x7ff8000000000000UL; \
} \
else { \
- float_uint_union.f = (v); \
+ float_uint_union.f = (f); \
} \
- r.u = float_uint_union.u; \
+ r.u = float_uint_union.u + 0x8004000000000000; \
} while(0)
#define NANBOX_SET_VALUE(o, tt, v) do { \
- (o).u = ((0xfff0|(tt))<<48) | (v).u; \
+ (o).u = ((uint64_t)tt<<48) | (uint64_t)(v); \
} while (0)
+#define mrb_float_p(o) (((uint64_t)(o.u)&0xfffc000000000000) != 0)
+
MRB_INLINE enum mrb_vtype
mrb_type(mrb_value o)
{
- if ((o.u >> 52) == 0xfff) return MRB_TT_FLOAT;
- switch ((o.u >> 48) & 7) {
- case MRB_NANBOX_TT_OBJECT: {
- uintptr_t u = o.u & ~((~0)<<48);
- return ((struct RBasic *)u)->tt;
+ if (mrb_float_p(o)) return MRB_TT_FLOAT;
+
+ uint64_t u = o.u;
+ switch ((enum mrb_nanbox_tt_inline)((u >> 48) & 3)) {
+ case MRB_NANBOX_TT_POINTER: {
+ if (u == 0) return MRB_TT_FALSE;
+ if (u & 1) return MRB_TT_CPTR;
+ return ((struct RBasic*)(uintptr_t)u)->tt;
}
case MRB_NANBOX_TT_INTEGER:
return MRB_TT_INTEGER;
case MRB_NANBOX_TT_SYMBOL:
return MRB_TT_SYMBOL;
- case MRB_NANBOX_TT_POINTER:
- return MRB_TT_CPTR;
case MRB_NANBOX_TT_MISC:
- return (enum mrb_vtype)(o.u >> 5) & 0x1f;
+ return (enum mrb_vtype)(o.u >> 8) & 0x1f;
default:
+ /* never happen */
return MRB_TT_FLOAT;
}
}
-#define mrb_fixnum(o) ((mrb_int)((uintptr_t)0xffffffff)&((o).u))
+#define NANBOX_SET_MISC_VALUE(r,t,i) NANBOX_SET_VALUE(r, MRB_NANBOX_TT_MISC, ((t)<<8) | i)
+
+#define mrb_float(o) mrb_nan_boxing_value_float(o)
+#define mrb_fixnum(o) ((mrb_int)(((uintptr_t)0xffffffff)&((o).u)))
#define mrb_integer(o) mrb_fixnum(o)
#define mrb_symbol(o) ((mrb_sym)((uintptr_t)0xffffffff)&((o).u))
-#define mrb_ptr(o) ((void*)(((uintptr_t)0xfffffffffff)&((o).u)))
-#define mrb_cptr(o) mrb_ptr(o)
+#define mrb_ptr(o) ((void*)(uintptr_t)(o).u)
+#define mrb_cptr(o) ((void*)(uintptr_t)(0xfffffffffffe&(o).u))
#define SET_NIL_VALUE(r) NANBOX_SET_MISC_VALUE(r, MRB_TT_FALSE, 0)
#define SET_FALSE_VALUE(r) NANBOX_SET_MISC_VALUE(r, MRB_TT_FALSE, 1)
#define SET_TRUE_VALUE(r) NANBOX_SET_MISC_VALUE(r, MRB_TT_TRUE, 1)
-#define SET_BOOL_VALUE(r,b) NANBOX_SET_MISC_VALUE(r, b ? MRB_TT_TRUE : MRB_TT_FALSE, 1)
+#define SET_BOOL_VALUE(r,b) NANBOX_SET_MISC_VALUE(r, (b) ? MRB_TT_TRUE : MRB_TT_FALSE, 1)
#define SET_INT_VALUE(mrb,r,n) SET_FIXNUM_VALUE(r,n)
#define SET_FIXNUM_VALUE(r,n) NANBOX_SET_VALUE(r, MRB_NANBOX_TT_INTEGER, (uint32_t)(n))
#define SET_SYM_VALUE(r,v) NANBOX_SET_VALUE(r, MRB_NANBOX_TT_SYMBOL, (uint32_t)(v))
-#define SET_OBJ_VALUE(r,v) NANBOX_SET_VALUE(o, MRB_NANBOT_TT_OBJECT, v)
-#define SET_CPTR_VALUE(mrb,r,v) NANBOX_SET_VALUE(o, MRB_NANBOT_TT_POINTER, v)
+#define SET_OBJ_VALUE(r,v) do {(r).u = (uint64_t)(uintptr_t)v;} while (0)
+#define SET_CPTR_VALUE(mrb,r,v) do {(r).u = ((uint64_t)(uintptr_t)v) | 1;} while (0)
#define SET_UNDEF_VALUE(r) NANBOX_SET_MISC_VALUE(r, MRB_TT_UNDEF, 4)
+#define mrb_nil_p(o) (mrb_type(o) == MRB_TT_FALSE && ((o).u & 3) == 0)
+#define mrb_false_p(o) (mrb_type(o) == MRB_TT_FALSE && ((o).u & 2) == 0)
+
#endif /* MRUBY_BOXING_NAN_H */

boxing_nan.h: implement Favor pointer NaN Boxing.

Favor pointer means encode NaN boxed values to keep pointer values
unmodified, to reduce the cost of far frequent pointer value retrievals.