| Re: understanding 'fix' command! [message #59828 is a reply to message #59823] |
Fri, 18 April 2008 09:32  |
Foldy Lajos
Messages: 268
Registered: October 2001
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Senior Member |
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On Fri, 18 Apr 2008, vino wrote:
> Hi!
> I was trying out the 'FIX' command and i couldnt understand all the
> arguments present. Can someone help me please? below is whats i did!
> IDL> c=[1.2,-3.4,5.]
> IDL> print,fix(c)
> 1 -3 5
You have converted a float array to int.
FIX converts to IDL int, which is 16 bits wide, is signed and its range is
-32768 <= int <= 32767. I assume you know how numbers are represented in
computers. (The following is valid on little-endian machines only.)
Your float array occupies 12 bytes in memory, namely:
154 153 153 63 154 153 89 192 0 0 160 64 (in decimal)
> IDL> print,fix(c,0)
> -26214
reads memory as int from offset 0: the two bytes 154, 153 give -26214
(154+256*153 = 39322 = 65536-26214 = -26214)
> IDL> print,fix(c,1)
> -26215
reads memory as int from offset 1: the two bytes 153, 153 give -26215
(153+256*153 = 39321 = 65536-26215 = -26215)
> IDL> print,fix(c,2)
> 16281
reads memory as int from offset 2: the two bytes 153, 63 give 16281
(153+256*63 = 16281)
> IDL> print,fix(c,0,1)
> -26214
same as first, reads 1 int (from offset 0)
> IDL> print,fix(c,0,2)
> -26214 16281
>
same as first and third, reads 2 ints (from offset 0 and 2)
regards,
lajos
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