comp.lang.idl-pvwave archive - RDF feed
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description: Messages from Usenet group comp.lang.idl-pvwave, compiled by Paulo Penteado
items: Re: Hex constants interpreted differently in IDL/v5.2

Re: Hex constants interpreted differently in IDL/v5.2
type: item
description: William Thompson (thompson@orpheus.nascom.nasa.gov) writes: > Apparently, IDL/v5.2 interprets some hexadecimal constants differently than > previous versions. For example, the statement > > IDL> help,'aa7f'x > > under IDL/v5.1 produces the result > > <Expression> LONG = 43647 > > while under IDL/v5.2, the following is returned > > <Expression> INT = -21889 Yep. I think I reported this already. (Or meant to, if I didn't.) I first noticed it with this kind of syntax: Plot, data, Color='00ffff'x This used to draw a yellow plot, but started drawing white plots in IDL 5.2. Of course, the previous behavior was decidedly a bug (that I had gotten used to, darn it), but if you want a 24-bit number, you really do need to make it a long: Plot, data, color='00ffff'xL I presume the bug was found and fixed when the programmers were implementing the unsigned integer data type. :-) Cheers, David -- David Fanning, Ph.D. Fanning Software Consulting Phone: 970-221-0438 E-Mail: davidf@dfanning.com Coyote's Guide to IDL Programming: http://www.dfanning.com/ Toll-Free IDL Book Orders: 1-888-461-0155
creator: davidf
date: 1999-05-24T07:00:00-00:00

Re: Hex constants interpreted differently in IDL/v5.2
type: item
description: thompson@orpheus.nascom.nasa.gov (William Thompson) writes: > A colleague of mine (Craig DeForrest) pointed this out to me, and I thought it > important enough to distribute more widely. Has anybody else run into this > one? > Apparently, IDL/v5.2 interprets some hexadecimal constants differently than > previous versions. For example, the statement > IDL> help,'aa7f'x > under IDL/v5.1 produces the result > <Expression> LONG = 43647 > while under IDL/v5.2, the following is returned > <Expression> INT = -21889 Update -- I just heard that RSI considers this a bug, because v5.2 acts differently in this regard than all earlier versions of IDL. The next version of IDL should go back to the old behavior. Bill Thompson
creator: thompson
date: 1999-05-25T07:00:00-00:00

Re: Hex constants interpreted differently in IDL/v5.2
type: item
description: In an earlier message, I had written > To be affected, the hexadecimal constant needs to be exactly four bytes long, ^^^^^^^^^^ Oops, I meant to say "four nibbles" (i.e. two bytes). :^) Bill Thompson
creator: thompson
date: 1999-05-25T07:00:00-00:00

Re: Hex constants interpreted differently in IDL/v5.2
type: item
description: David Fanning wrote: > > William Thompson (thompson@orpheus.nascom.nasa.gov) writes: > >> Apparently, IDL/v5.2 interprets some hexadecimal constants differently than >> previous versions. For example, the statement >> >> IDL> help,'aa7f'x >> >> under IDL/v5.1 produces the result >> >> <Expression> LONG = 43647 >> >> while under IDL/v5.2, the following is returned >> >> <Expression> INT = -21889 > > Yep. I think I reported this already. (Or meant to, > if I didn't.) > > I first noticed it with this kind of syntax: > > Plot, data, Color='00ffff'x > > This used to draw a yellow plot, but started drawing > white plots in IDL 5.2. Of course, the previous behavior > was decidedly a bug (that I had gotten used to, darn it), > but if you want a 24-bit number, you really do need to > make it a long: > > Plot, data, color='00ffff'xL > > I presume the bug was found and fixed when the programmers > were implementing the unsigned integer data type. :-) > > Cheers, > > David Why should this be a bug? With '00ffff'x you are specifying 3 bytes, hence you need at least a long variable. I would think it's OK if this is interpreted as such. For the cases that William mentions, it i sarguable whether the correct behaviour should be to produce an unsigned int instead of a 'normal' int. At least in my experience, hex numbers are usually meant to be positive. And you could still force it as fix('f000'x). Regards, Martin -- |||||||||||||||\\\\\\\\\\\\\-------------------///////////// //||||||||||||||| Martin Schultz, DEAS, Harvard University, 29 Oxford St., Pierce 109, Cambridge, MA 02138 phone (617) 496 8318 fax (617) 495 4551 e-mail mgs@io.harvard.edu web http://www-as/people/staff/mgs/
creator: Martin Schultz
date: 1999-05-25T07:00:00-00:00