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Re: modulo reset [message #41702 is a reply to message #41700]

Tue, 23 November 2004 07:52

Wayne Landsman
Messages: 117
Registered: January 1997

Senior Member

Ralf Schaa wrote:
> I'm reading out some binary data and the description says this about a
> data field :
>
> in the case of a modulo reset add 2^32
>
> What is this about? googling for "modulo reset" didn't get me far;
> I only imagine that I need some kind of overflow to get things fixed,
> but it is very unclear to me what is happening and why ...

Well, my first guess is that you are working with unsigned 32bit
integers which have a maximum value of 2^32-1, and then resets to zero.

STIS>print,2UL^31,2UL^32
2147483648 0

The easiest way to correct for this reset would be to use 64 bit integers

data = ulong64(datafield) + 2ULL^32

A less likely possiblity is that "modulo reset" refers to a 32bit
checksum, e.g. as implemented in
http://idlastro.gsfc.nasa.gov/ftp/pro/misc/checksum32.pro
which includes links to more documentation.

Good Luck, --Wayne Landsman

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[Message index]

		Re: modulo reset By: Ralf Schaa on Tue, 23 November 2004 08:39
		Re: modulo reset By: Wayne Landsman on Tue, 23 November 2004 07:52
		Re: modulo reset By: James Kuyper on Tue, 23 November 2004 10:51

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