On Tuesday, November 13, 2018 1:06:01 PM PST Zhijie Li wrote:
> Hi Ethan,
> Thanks for the information. My guess is that in MTZ only F-float is expected,
> because it is the only 32bit form?
I do not remember exactly what was used for mtz files at that time.
It might have been REAL*4 or it might have been REAL*8.
<\me rummages along the shelf above my desk>
Looking here at my trusty VAX-11 Fortran manual from April 1982,
D_floating was the default for REAL*8.
F_floating: 1 bit sign, 8 bit exponent, 23 bit mantissa
D_floating: 1 bit sign, 8 bit exponent, 55 bit mantissa
G_floating: 1 bit sign, 11 bit exponent, 52 bit mantissa
Later on they introduced H_floating, S_floating, T_floating and probably an
entire
zoo that went extinct shortly after.
Bit assignments:
https://nssdc.gsfc.nasa.gov/nssdc/formats/VAXFloatingPoint.htm
Ethan
> Zhijie
>
> > On Nov 13, 2018, at 3:44 PM, Ethan A Merritt <merr...@u.washington.edu>
> > wrote:
> >
> >> On Tuesday, November 13, 2018 11:51:55 AM PST Zhijie Li 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.
> >
> > It's more complicated than that. VAXen supported multiple floating point
> > formats,
> > F-floating G-floating and H-floating.
> > They had differed by how many bits were used for the exponent, and hence how
> > many bits were left for the mantissa.
> > I can pull out the architecture manuals if necessary.
> >
> > ah, nostalgia
> >
> > Ethan
> >
> >
> >> 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 <hat...@ucla.edu> 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 <zhijie...@utoronto.ca> 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
> >>>>> <0000270165b9f4cf-dmarc-requ...@jiscmail.ac.uk> 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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> >>>>
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> >>>>
> >>>
> >>> Research Specialist @ Gonen Lab
> >>> ____________________________________________________
> >>> UCLA * 615 Charles E. Young Drive South
> >>> BSRB #347 * Los Angeles, CA 90095
> >>>
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> >
> >
> > --
> > Ethan A Merritt
> > Biomolecular Structure Center, K-428 Health Sciences Bldg
> > MS 357742, University of Washington, Seattle 98195-7742
> >
> >
> >
>
--
Ethan A Merritt
Biomolecular Structure Center, K-428 Health Sciences Bldg
MS 357742, University of Washington, Seattle 98195-7742
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