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Re: signed character [message #30412]

Thu, 25 April 2002 06:24

Mark Rivers
Messages: 49
Registered: February 2000

Member

Carmen <cambicambi@hotmail.com> wrote in message
news:8128b197.0204250239.509a20fb@posting.google.com...
> Hello,
>
> I am trying to access information stored in a matrix, byte per byte.
> If I were using C, I should read every byte as SIGNED CHARACTERS.
> But, IDL has not that definition.
>
> I would appreciate a lot if you can tell me what should I do in order
> to read the data correctly.

If A is the matrix containing an IDL byte array (which IDL assumes is
unsigned) then you could do

; First convert A to a signed 16-bit integer array
a = fix(a)
; Find the indices of the negative elements (MSB of 8-bit value set)
negs = where(a and '80'x)
; Extended the sign to 16 bits
a[negs]=a[negs] or 'ff80'x

The drawbacks of this approach are that your matrix is twice as big (16 bits
vs 8 bits), and that you need to create the temporary array "negs". If your
matrix is only 2-D and not terribly huge then this should be fine.

Mark Rivers

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[Message index]

		Re: signed character By: Mark Rivers on Thu, 25 April 2002 06:24
		Re: signed character By: Dick Jackson on Thu, 25 April 2002 06:19

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