Intel x86-64 now fully supported using Microsoft Visual C++ (Visual Studio)
Note that this environment does NOT support inline assembly, so built-in
intrinsics must be used instead, like umul128()

Use a header file like 

#define MR_LITTLE_ENDIAN
#define MIRACL 64
#define mr_utype __int64
#define MR_IBITS 32
#define MR_LBITS 32
#define mr_unsign32 unsigned int
#define mr_unsign64 unsigned __int64
#define MR_FLASH 52
#define MAXBASE ((mr_small)1<<(MIRACL-1))
#define BITSINCHAR 8

and use the file mrmuldv.w64 as mrmuldv.c

There is also a macro file win64.mcs  - see kcmcomba.txt and makemcs.txt

To build the windows x86-64 miracl library, execute the batch file ms64doit.bat