Subject: Word-Alignment Question

From: [email-masked] (Don Wells)
Date: Sat, 21 Apr 90 14:45:14 EDT

Frank Ghigo asks [From [email-masked] Wed Apr  4 13:40:04
1990 To: [email-masked] Subject: more FITS queries]:

"Here is another question:  are IEEE reals and doubles required to be
aligned on 4-byte boundaries within a FITS binary table?  or are there
any alignment rules for these numbers?  I am under the impression that
there is no such requirement, but this point does not seem to be
mentioned in any of the official FITS writeups I've seen."

I am sending Frank's query and my answer to DISHFITS because it falls
into the "most frequently asked questions" category.

The answer is *no*, R*4 and R*8 values are not to be aligned modulo 4
or 8. Indeed, Bill Cotton specifies that the data from successive
columns in a row should be one contiguous stream, and he even
explicitly says (in the draft of the 3-D tables paper, which I am
currently reviewing) that "NAXIS1 (integer) is the number of 8 bit
bytes in each 'row'. This should correspond to the sum of the values
defined in the TFORMnnn keywords."

-Don