| hexadecimal variables [message #15093] |
Wed, 21 April 1999 00:00  |
Pavel Romashkin
Messages: 166
Registered: April 1999
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Senior Member |
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Hi,
Is there a nice way to convert hexadecimal variables? Here's what I am
trying to do:
This is received from the outside.
h_string = '40000FC0DA'
h_long = long(h_string)
This, obviously, fails to recognize alphabetical hexadecimal part and
sets h_long to 40,000.
temp = execute("h_long = long(' "+h_string+" 'x)")
This, naturally, works, setting h_long to the desired 1032410, but looks
quite ugly. Besides, it is 3 times slower than without "execute" - not
really a concern on fast machines, but inefficient code just bugs me.
I am sure I am missing something here. Can anyone suggest a neater way
to do this? Maybe, there is a way to use Z-formatted READ here?
Thank you,
Pavel
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| Re: hexadecimal variables [message #15167 is a reply to message #15093] |
Fri, 23 April 1999 00:00  |
wmc
Messages: 117
Registered: February 1995
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Senior Member |
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Pavel Romashkin <promashkin@cmdl.noaa.gov> wrote:
> This is received from the outside.
> h_string = '40000FC0DA'
> h_long = long(h_string)
> This, obviously, fails to recognize alphabetical hexadecimal part and
> sets h_long to 40,000.
> temp = execute("h_long = long(' "+h_string+" 'x)")
> This, naturally, works, setting h_long to the desired 1032410
As others have pointed out, its a 64 bit string.
Looking at your "execute", I thought that
wmc> h_long = long(h_string+''x)
Ought to work, but it produces
wmc> print,h_long
-2556760
(I'd forgotten that its a 64-bit string)
However,
wmc> h_long = long64(h_string+''x)
Seems to work perfectly well
wmc> print,h_long
4398043954346
- William
--
William M Connolley | wmc@bas.ac.uk | http://www.nbs.ac.uk/public/icd/wmc/
Climate Modeller, British Antarctic Survey | Disclaimer: I speak for myself
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| Re: hexadecimal variables [message #15175 is a reply to message #15093] |
Thu, 22 April 1999 00:00 |
Vapuser
Messages: 63
Registered: November 1998
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Member |
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Pavel Romashkin <promashkin@cmdl.noaa.gov> writes:
> Hi,
> Is there a nice way to convert hexadecimal variables? Here's what I am
> trying to do:
>
> This is received from the outside.
> h_string = '40000FC0DA'
>
> h_long = long(h_string)
> This, obviously, fails to recognize alphabetical hexadecimal part and
> sets h_long to 40,000.
>
> temp = execute("h_long = long(' "+h_string+" 'x)")
> This, naturally, works, setting h_long to the desired 1032410,
This is not what h_long equals; 1032410 = 'fc0da'x. You've only gotten
the first 32 bits. See below.
> but looks
> quite ugly. Besides, it is 3 times slower than without "execute" - not
> really a concern on fast machines, but inefficient code just bugs me.
>
> I am sure I am missing something here. Can anyone suggest a neater way
> to do this? Maybe, there is a way to use Z-formatted READ here?
>
> Thank you,
> Pavel
>
40000FC0DA is larger than 32 bits. Unless you're using idl 5.2,
having access to 64 bit integers, you're out of luck, without kluging
together something having the same flavor as a 'far' pointer in old
MS-DOS.
The general method, however, is to use reads, which works on scalars
and arrays. Here's an example, using IDL 5.2, and 64 bit integers.
IDL> h='40000FC0DA'
IDL> x=0LL
IDL> help,x
X LONG64 = 0
IDL> reads,h,x,form='(Z)'
IDL> print,x,form='(z)'
40000fc0da
IDL> print,x
274878939354
IDL>
If you try this in idl<5.2,(with x=0L) you'll only get the right
most 32 bits, i.e. X = 'fc0da'x. Witness...
IDL> x1=0L
IDL> reads,h,x1,form='(Z)'
IDL> print,x1
1032410
IDL> print,x1,form='(z)'
fc0da
If you really need the > 32 bits, you're going to have to use idl
5.2, or read it, split it, and recombine it as a double?
--
William Daffer
vapuser@catspaw.jpl.nasa.gov
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| Re: hexadecimal variables [message #15177 is a reply to message #15093] |
Thu, 22 April 1999 00:00 |
Pavel Romashkin
Messages: 166
Registered: April 1999
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Senior Member |
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Dick,
I appreciate it! It is certainly what I looked for, and I was looking for
READS yesterday before I wrote a question. But, apparently quite dumb by the
end of the day, I typed "READ" in the search string, naively thinking that
all READ-related functions will be there. READ/READF surely are, but READS
happened to be separate. And, after using IGOR and IDL at the same time, I
thought I rememberd seeing READS among IGOR's functions.
However, after I tried READS, it is even slower than "execute" (by 0.02 s but
still)! That is strange. I guess compiling a string takes less time than
string conversion. READS might appear more efficient if a string to pass to
"execute" was more complicated.
Dick Jackson wrote:
> You've got it, using ReadS (read from string). It looks like you have five
> bytes so you need a very long integer to store this, giving me the first
> chance I've had to use IDL 5.2's new data types:
Well, in fact I have 8 bytes (in the real data) but I am checking only on
bits 12 and 13, so even INT will do. If I need to check on higher level
bits, I can cut the string apart.
Thanks again,
Pavel
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| Re: hexadecimal variables [message #15224 is a reply to message #15093] |
Mon, 26 April 1999 00:00 |
wmc
Messages: 117
Registered: February 1995
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Senior Member |
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wmc@bas.ac.uk wrote:
> Pavel Romashkin <promashkin@cmdl.noaa.gov> wrote:
>> h_string = '40000FC0DA'
> wmc> h_long = long64(h_string+''x)
> Seems to work perfectly well
> wmc> print,h_long
> 4398043954346
Oops, I didn't check this properly. I just looked at the above & thought it
was about right, but IDL has been fooling me:
I thought the string+''x syntax ought to work (why doesn't it?) but it doesn't,
it just doesn't always generate an error message. Oh dear. In fact:
wmc> h_string='10' & h_long = long(h_string+''x) & print,h_long
-2596734
wmc> h_string='10' & h_long = long(h_string+''xl) & print,h_long
h_string='10' & h_long = long(h_string+'
^
% Long integer constant must be less than 2147483648.
I'm confused..., but I suspect IDL is too...
-W
btw: { alpha OSF unix 5.2 Oct 30 1998}
--
William M Connolley | wmc@bas.ac.uk | http://www.nbs.ac.uk/public/icd/wmc/
Climate Modeller, British Antarctic Survey | Disclaimer: I speak for myself
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