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add commentary to value representation

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This commit is contained in:
Yuichi Nishiwaki
2013-08-04 01:08:11 -07:00
parent 94a6d8380f
commit dd2ea59d61
1 changed files with 8 additions and 0 deletions
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include/mruby/value.h
+8
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@@ -144,6 +144,14 @@ typedef struct mrb_value {
};
} mrb_value;
/* value representation by nan-boxing:
* float : FFFFFFFFFFFFFFFF FFFFFFFFFFFFFFFF FFFFFFFFFFFFFFFF FFFFFFFFFFFFFFFF
* object: 111111111111TTTT TTPPPPPPPPPPPPPP PPPPPPPPPPPPPPPP PPPPPPPPPPPPPPPP
* int : 1111111111110000 1000000000000000 IIIIIIIIIIIIIIII IIIIIIIIIIIIIIII
* sym : 1111111111110000 1010000000000000 SSSSSSSSSSSSSSSS SSSSSSSSSSSSSSSS
* In order to get enough bit size to save TT, all pointers are shifted 2 bits
* in the right direction.
*/
#define mrb_tt(o) (((o).value.ttt & 0xfc000)>>14)
#define mrb_mktt(tt) (0xfff00000|((tt)<<14))
#define mrb_type(o) ((uint32_t)0xfff00000 < (o).value.ttt ? mrb_tt(o) : MRB_TT_FLOAT)