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From: nahaj@u.cc.utah.edu (John Halleck)
Subject: Binary files vs Portablity vs Ada
Date: 1999/11/04
Message-ID: <7vt67r$qv0$1@coward.ks.cc.utah.edu>#1/1
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Organization: University of Utah - ACLIS
NNTP-Posting-Date: 4 Nov 1999 23:52:27 GMT
Newsgroups: comp.lang.ada
Date: 1999-11-04T23:52:27+00:00
List-Id: <comp.lang.ada>

Background:

  At one time I wrote a version of the Standard Hash Algorithm (SHA, 
  it went with the old government Digital Signature Standard)
  which I wrote in C...

  Lately, because GNAT is now around, I've hauled it out again,
  and redid it in Ada.  I then used it as an example for a coworker
  as to how you can be portable in Ada.

  The actual algorithm is defined for a bit stream, although almost
  everyone implements it for bits in byte size chunks. (As I did)
  Because of this, any file should be Hashable, even on machines
  with perverse word and byte sizes. 

Question:

  Is there even a portable way to get the "raw" bits for a file that
  works on all machines supporting Ada?  (So that it can be handed
  to a bit oriented version of SHA.)

  It is not hard to do something that just grabs bytes from a file
  until done, but that assumes the file is some multiple of eight
  bits long, and that all data for the file is in the bytes returned.
  On machines like the Sperry 1100 series, the native word size is
  36 bits (Usually chopped into four nine-bit bytes for Text use)
  And the file is "control word -> image"  instead of "embeded
  control."

  Can this be done portabily?  (I suspect not, but I'm not an Ada
  expert.)  I have something that seems to work for PC's, Mac's, 
  and Unix boxes, but it bugs me that I don't know how to do it in
  any general way.