[sac-dev] byte order and swapping

[George Helffrich]

 From Arthur Snoke's response:

> ... I don't agree with your statement that the byte order cannot be 
> discerned easily for SGF files.  The first "word" in an SGF file is a 
> 4-byte integer which is (using od -t -d2 on the Sun) 00000   00005 for 
> big endian and 01280   00000 on PC/Linux.  Am I missing something?

The reason Arthur's tactic works is because SAC always writes SGF files 
with a stanza that writes:

   bufsize:    16
   color:     7
   line:     1
   hwsize:       0.013       0.020     1     7
   color:     7
   no-op:

There is nothing to prevent an internal change in SAC that would not 
write these commands in this order;  if SAC were to flush its internal 
buffer later than it does, the magic word at the front would have a 
value different from 5.

Because there isn't anything in the SGF specification that requires 
this buffer be exactly this size and written in that order, the 
endianness of an SGF file cannot be reliably determined.

Next, Brian Savage's response:

> At present we still have a problem with the readhdr/writehdr routines 
> and this needs to be fixed.

MacSAC does not have this bug.  Not because it is as clever as Brian's 
proposal for SAC's handling of readhdr/writehdr, but because all files 
that MacSAC reads or writes are big-endian.  If we specify an 
endianness, there is no bug to be fixed.


                                                                         
      George Helffrich
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