| Re: Endian-ness [message #29307 is a reply to message #29233] |
Mon, 11 February 2002 07:16   |
Jonathan Joseph
Messages: 69
Registered: September 1998
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Member |
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Thank you David and Liam,
Liam's result seems more aesthetically pleasing (no offense David).
Unfortunately, I don't think I can use the swap_if_big_endian and
swap_if_little_endian keywords to OPEN, because whether I swap or
not depends on BOTH the hardware and the file. I have no a-priori
knowledge of the endian-ness of the file until I've already
opened it. Although, I guess I could open the file, figure out
what it is, close it and then re-open it. The file has a text header
(impervious to byte-order issues) that will indicate the endian-ness
of the file, followed by binary data.
Am I correct in assuming that Liam's functions don't need to be
specifically cast to Long? In other words,
byte(1,0) would yield the same result as byte(1L, 0L)
Thanks.
-Jonathan
"Liam E. Gumley" wrote:
>
> Jonathan Joseph wrote:
>> Is there a system variable that gives the endian-ness of the current
>> hardware? I am reading a file which tells me the endian-ness of the
>> data, and I'd like to swap_endian if it is different from the current
>> hardware. In lieu of finding a system variable to compare to, I have
>> done this:
>>
>> test_int = 1
>> byteorder,test_int,/ntohs
>> big_endian = test_int eq 1
>>
>> "network" byte order is big-endian, so I convert a 1 to the host
>> byte-order and see if it's still a 1.
>>
>> This way works fine, but it seems as thought I'm missing something.
>> Is there a better way? Using the byteorder routine to convert the data
>> is not an option (unless it's been improved for 5.5).
>
> ;---
> FUNCTION BIG_ENDIAN
>
> ;- Returns true (1B) if the host platform is big endian
> ;- (most significant byte first)
>
> return, 1B - byte(1L, 0L)
>
> END
> ;---
> FUNCTION LITTLE_ENDIAN
>
> ;- Returns true (1B) if the host platform is little endian
> ;- (least significant byte first)
>
> return, byte(1L, 0L)
>
> END
> ;---
>
> IDL Version 5.3 (IRIX mipseb). (c) 1999, Research Systems, Inc.
> IDL> print, big_endian(), little_endian()
> 1 0
>
> IDL Version 5.3 (Win32 x86). (c) 1999, Research Systems, Inc.
> IDL> print, big_endian(), little_endian()
> 0 1
>
> Cheers,
> Liam.
> Practical IDL Programming
> http://www.gumley.com/
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