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From: eachus@spectre.mitre.org (Robert I. Eachus)
Subject: Re: Looking for generic hash function
Date: 1996/08/19
Message-ID: <EACHUS.96Aug19172952@spectre.mitre.org>#1/1
X-Deja-AN: 175177006
references: <4v23jd$mg9@News.Dal.Ca>
organization: The Mitre Corp., Bedford, MA.
newsgroups: comp.lang.ada
Date: 1996-08-19T00:00:00+00:00
List-Id: <comp.lang.ada>


In article <4v23jd$mg9@News.Dal.Ca> grandyre@newton.ccs.tuns.ca (Robert Grandy) writes:

  > The function would return a pretty much random Integer based on its
  > generic parameter. I was thinking of using the 'size attribute, but
  > does anyone have any other suggestions.

   This is one case where I wouldn't complain about someone converting
a value of type System.Address to an Integer (assuming Ada 95):

  with System.Storage_Elements;
  function get_data_id return Integer is 
    Foo: Integer;
  begin
    return Integer(System.Storage_Elements.To_Integer(Foo'ADDRESS));
  exception
    when others =>
      return Integer(System.Storage_Elements.To_Integer(Foo'ADDRESS)
         mod System.Storage_Elements.Integer_Address(Integer'LAST));
      -- this return statement can only raise an exception when the
      -- previous one does not.
  end get_data_id;

    Note that, if Integer is 32-bits then every instance will create
its own return value.  And if all instances are at library level and
one per type, then the value returned for a particular type will be
unique within the partition.  If this is not what you are looking for
there are other variants.


					Robert I. Eachus

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--

					Robert I. Eachus

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