| Re: 4-bit words [message #5409] |
Fri, 22 December 1995 00:00 |
orbach
Messages: 9
Registered: June 1994
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Junior Member |
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In message <DJxwrH.ou@midway.uchicago.edu> - rivers@cars3.uchicago.edu (Mark
Rivers) writes:
:>
:>In article <DJw3nF.D8n@rockyd.rockefeller.edu>, orbach@rockvax.rockefeller.edu (Darren Orbach) writes:
:>>I have a file that consists of a 256*256 array of 4-bit
:>>words created in another application, written as a binary
:>>file. I need to manipulate this array by shifting these
:>>4-bit elements to the right by various amounts, and wrapping
:>>around to the other side of the array. However, since the
:>>smallest data type in WAVE or IDL is a full byte, I don't see
:>>a straightforward way to do this. Any suggestions?
:>
:>I am assuming that your data files have the 4-bit values packed together. If so
:>then the following should create the array you want:
:>
:>; Make a 1-D byte array big enough to hold image from disk
:>IDL> temp = bytarr(2L^15)
:>; Read in the data
:>IDL> readu, lun, temp
:>; Make new array to hold decomposed data
:>IDL> data = bytarr(2, 2L^15)
:>; Low order 4 bits in even elements
:>IDL> data(0,*) = (temp and '00FF'X)
:>; High order 4 bits in odd elements
:>IDL> data(1,*) = (temp/16 and '00FF'X)
:>; Reform into 256x256 array
:>IDL> data = reform(data, 256, 256)
:>
:> ____________________________________________________________
:>Mark Rivers (312) 702-2279 (office)
:>CARS (312) 702-9951 (secretary)
:>Univ. of Chicago (312) 702-5454 (FAX)
:>5640 S. Ellis Ave. (708) 922-0499 (home)
:>Chicago, IL 60637 rivers@cars3.uchicago.edu (Internet)
:>
Mark's suggestion worked nicely, with the proviso that the hex
number to use is '000F'x. The rest of the procedure involved
bit-shifting to the right, keeping proper account of where
high bits are so formed & moving them separately, and then
re-packing the data(2, 2L^15) array back into a temp(1, 2L^15)
array with the operation temp = (data(0,*) or data(1,*)).
Thanks to all.
-Darren Orbach
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| Re: 4-bit words [message #5415 is a reply to message #5411] |
Thu, 21 December 1995 00:00  |
David S. Foster/Admin
Messages: 14
Registered: May 1995
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Junior Member |
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orbach@rockvax.rockefeller.edu (Darren Orbach) wrote:
>
> I have a file that consists of a 256*256 array of 4-bit
> words created in another application, written as a binary
> file. I need to manipulate this array by shifting these
> 4-bit elements to the right by various amounts, and wrapping
> around to the other side of the array. However, since the
> smallest data type in WAVE or IDL is a full byte, I don't see
> a straightforward way to do this. Any suggestions?
I think I would write a routine that reads in the data two
elements (8 bits) at a time, then extract the two elements
from the byte, and puts these two bytes into a
corresponding 256x256 array of bytes; then manipulate
this byte array.
Given a byte of data stored in 'value':
val = value
lo = 0B
for i = 0, 3 do begin
higher_bit = 2L ^ long(i+1)
rem = val mod higher_bit
if (rem ne 0) then begin
lo = lo + 2L ^ long(i)
val = val - rem
endif
endfor
hi = 0B
for i = 4, 7 do begin
higher_bit = 2L ^ long(i+1)
rem = val mod higher_bit
if (rem ne 0) then begin
hi = hi + 2L ^ long(i-4)
val = val - rem
endif
endfor
This *should* give the lower and upper halves of the original byte,
as two byte values, 'lo' and 'hi'. I've tested this and it seems
to work. But hey, my job description says that my programming
only has to be 90% accurate!
Wouldn't it be nice if IDL had bitwise operators!
Dave Foster
foster@bial6.ucsd.edu
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| Re: 4-bit words [message #5421 is a reply to message #5411] |
Thu, 21 December 1995 00:00 |
rivers
Messages: 228
Registered: March 1991
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Senior Member |
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In article <DJw3nF.D8n@rockyd.rockefeller.edu>, orbach@rockvax.rockefeller.edu (Darren Orbach) writes:
> I have a file that consists of a 256*256 array of 4-bit
> words created in another application, written as a binary
> file. I need to manipulate this array by shifting these
> 4-bit elements to the right by various amounts, and wrapping
> around to the other side of the array. However, since the
> smallest data type in WAVE or IDL is a full byte, I don't see
> a straightforward way to do this. Any suggestions?
I am assuming that your data files have the 4-bit values packed together. If so
then the following should create the array you want:
; Make a 1-D byte array big enough to hold image from disk
IDL> temp = bytarr(2L^15)
; Read in the data
IDL> readu, lun, temp
; Make new array to hold decomposed data
IDL> data = bytarr(2, 2L^15)
; Low order 4 bits in even elements
IDL> data(0,*) = (temp and '00FF'X)
; High order 4 bits in odd elements
IDL> data(1,*) = (temp/16 and '00FF'X)
; Reform into 256x256 array
IDL> data = reform(data, 256, 256)
____________________________________________________________
Mark Rivers (312) 702-2279 (office)
CARS (312) 702-9951 (secretary)
Univ. of Chicago (312) 702-5454 (FAX)
5640 S. Ellis Ave. (708) 922-0499 (home)
Chicago, IL 60637 rivers@cars3.uchicago.edu (Internet)
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