[AstroPy] Reading JPL ephemeris files on 64-bit architecture

[Tom Kuiper]

I'm trying to get pynovas to work under Linux-AMD64 and have run into a 
problem reading the JPL ephemeris file.  I encountered this previously 
with Rick Fisher's jplephem but I think I have more of an insight now.  
The problem, I think, lies in this structure in ephem_types.h:

    struct recOneData {           /* storage on 
disk:                         */
          char label[3][84];      /* 3*84   =  252 bytes =  31.5 
words        */
          char constName[400][6]; /* 400*6  = 2400       = 300 
words          */
        double timeData[3];       /* 3*8    =   24       =   3 
words          */
           int numConst;          /* 1*4    =    4       =   0.5 words, 
32-bit long */
        double AU;                /* 1*8    =    8       =   1 
words          */
        double EMRAT;             /* 1*8    =    8       =   1 
words          */
           int coeffPtr[12][3];   /* 12*3*4 =  144       =  18 words, 
32-bit longs */
           int DENUM;             /* 1*4    =    4       =   0.5 words, 
32-bit long */
           int libratPtr[3];      /* 3*4    =   12       =   1.5 words, 
32-bit long */
                                  /*        = 2856 bytes = 357 words */
      };

I've annotated the original code.  Also, the original 32-bit code had 
longs instead of ints.  Changing them to ints made no difference.  The 
first int, numConst, comes out the same (wrong value) either way. I've 
verified this structure using the Python struct module.  The question: 
is there a way in C to ignore the fact that this structure doesn't 
respect 64-bit word boundaries?  I've considered using union but that 
would involve a lot of code changes, wherever this structure is used.

One solution to all this is, I suppose, to use bin2asc (after 
downloading and re-compiling the JPL ephemeris C source code) and 
generate a new ASCII data file for 64-bit machines.  I will if I have to 
but it seems more elegant to use the ephemeris binary files as they are 
given.  Any suggestions?

Thanks and regards,

Tom

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