[mpich-discuss] why (int)0x4c000101???

[ÄþÄþ ¶­]

when I read mpich2-1.4.1 code, I saw code as follow:

Code:
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18 typedef int MPI_Datatype;
#define MPI_CHAR           ((MPI_Datatype)0x4c000101)
#define MPI_SIGNED_CHAR    ((MPI_Datatype)0x4c000118)
#define MPI_UNSIGNED_CHAR  ((MPI_Datatype)0x4c000102)
#define MPI_BYTE           ((MPI_Datatype)0x4c00010d)
#define MPI_WCHAR          ((MPI_Datatype)0x4c00040e)
#define MPI_SHORT          ((MPI_Datatype)0x4c000203)
#define MPI_UNSIGNED_SHORT ((MPI_Datatype)0x4c000204)
#define MPI_INT            ((MPI_Datatype)0x4c000405)
#define MPI_UNSIGNED       ((MPI_Datatype)0x4c000406)
#define MPI_LONG           ((MPI_Datatype)0x4c000407)
#define MPI_UNSIGNED_LONG  ((MPI_Datatype)0x4c000408)
#define MPI_FLOAT          ((MPI_Datatype)0x4c00040a)
#define MPI_DOUBLE         ((MPI_Datatype)0x4c00080b)
#define MPI_LONG_DOUBLE    ((MPI_Datatype)0x4c000c0c)
#define MPI_LONG_LONG_INT  ((MPI_Datatype)0x4c000809)
#define MPI_UNSIGNED_LONG_LONG ((MPI_Datatype)0x4c000819)
#define MPI_LONG_LONG      MPI_LONG_LONG_INT 
Anyone can tell me what is the meaning of those hex values? and why does the author use them?
why do they define "MPI_CHAR" as ((MPI_Datatype)0x4c000101) instead of "char"?
thx
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