Hi Zhijie
It's definitely a factor 4. The code is in subroutine QTIEEE in the
Fortran source I mentioned previously at this line:
See line:
A(I)=((A(I)+SIGN(2,A(I)))/4.AND..NOT.MNAN).OR.MDN2
If you prefer it in C code it's in function vaxF2ieeeF in:
ccp4-7.0-src/checkout/libccp4/ccp4/vmslibrary.c
See line:
out.c[0] = buffer[i].c[1] - (uint8)1; /* subtracts 2 from exponent */
i.e. subtract 2 from exponent -> division by 4.
Cheers
-- Ian
On Tue, 13 Nov 2018 at 19:52, Zhijie Li <[email protected]> wrote:
> If somebody is going to send these files by email, please send one to me
> too. Thanks in advance. I actually prefer to get a MTZ file because the
> miller indices would serve as good clues for understanding the encodings.
> Even the first 1024 bytes of an MTZ would do (data array starts at byte 80
> in MTZ).
>
> In my life I had only seen ieee754. According to what I can find, VAX has
> an exponent bias of 128 (ieee754 uses 127). Then it seems to me that when
> converting from vax to ieee a division of 2 is involved. However all
> procedures I have seen use a division of 4, which is quite puzzling to me.
> A real data file containing meaningful numbers (eg., HKL indices) would be
> very helpful. Thanks in advance.
>
> Zhijie
>
> > On Nov 13, 2018, at 2:21 PM, Johan Hattne <[email protected]> wrote:
> >
> > Related by not exactly on topic: would anybody on the list be able to
> share old map files (not MTZ:s) with Convex, Cray, Fujitsu, or VAX
> reals/strings? I’d be interested to see what those files actually look(ed)
> like.
> >
> > // Best wishes; Johan
> >
> >> On Nov 9, 2018, at 18:38, Zhijie Li <[email protected]> wrote:
> >>
> >> Hi all,
> >>
> >> On linux there are a few good GUI HEX editors. Here I’d like to
> recommend BLESS, which conveniently displays all possible numerical
> interpretations of the four bytes under cursor. It also allows the user to
> switch between big endian or little endian through a checkbox.
> Unfortunately all floats are assumed to be IEEE754, therefore VAX floats
> won’t be interpreted correctly. ( The simplest way to convert vax to ieee
> float would be to write a little program to do some bit operations. I’d be
> happy to take that as my weekend project)
> >>
> >>
> >> BTW, along the line of space efficiency, I can’t help noticing that the
> miller indices are saved as float32 in mtz, as all other numbers in mtz.
> This certainly have made mtz format a beautiful homogeneous data format
> ;). In this particular case, if we have doubts about the reliability of
> the machine stamp, trying to restore the miller indices would be a good way
> to test hypotheses.
> >>
> >> Zhijie
> >>
> >>> On Nov 9, 2018, at 9:04 PM, James Holton <
> [email protected]> wrote:
> >>>
> >>> As a beamline scientist I must say I am glad that diffraction image
> data is not usually stored as ASCII text. In fact, I am slowly warming to
> the idea of storing it as not just binary, but compressed formats.
> Problem, I'm sure will be that it won't be long before we forget how to
> decompress them, as most of the algorithms we are using aren't all that
> widespread. Probably around the same time future generations will curse us
> for using ASCII instead of unicode, which is a 16-bit standard. I'm sure we
> will be reviled for limiting ourselves so, just to save a factor of two in
> disk space.
> >>> In situations like this I always use the unix "od" command. It makes
> everything "human readable" by converting the bytes into strings you can
> read. Then it is just a matter of figuring out what the bytes are.
> >>> Unfortunately, "od" only decodes floats on the native platform, so if
> the mtz is from another platform (Windows vs Linux, for example), then you
> might need to do some swapping. Thus far, I have encountered files that
> require one of a few swapping strategies in order to make them work:
> >>>
> >>> 1 2 3 4 - no swapping
> >>>
> >>> 4 3 2 1 - reverse all bytes
> >>>
> >>> 3 4 1 2 - swap words and swap bytes within the words
> >>> 2 1 4 3 - reverse of previous
> >>>
> >>> 2-1 1 4 3 - same as last, but if not all zero, decrement byte #2
> before swapping
> >>> 3 4 1 2+1 - same as 3412, but if not all zero increment byte #2 before
> swapping
> >>> I'm sure there are other combinations, but the oldest MTZ I have is
> only from 1996.
> >>>
> >>> -James Holton
> >>> MAD Scientist
> >>>
> >>>
> >>>> On 11/9/2018 4:47 AM, Eleanor Dodson wrote:
> >>>> Anyone any idea what to do about this?? Created in 1992!!
> >>>> Seems unreadable..
> >>>>
> >>>> No CTYP lines input for file: 1
> >>>> Indices output even if all data items flagged "missing"
> >>>> Warning, NOT all LABOUT data lines given
> >>>> Warning: Machine stamp corrupted? Assuming native format.
> >>>>>>>>>> CCP4 library signal library_file:End of File (Error)
> >>>>
> >>>>
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> >
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