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.

include/mruby/boxing_nan.h

@@ -25,111 +25,106 @@
 #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 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 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)(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 */