From mboxrd@z Thu Jan  1 00:00:00 1970
X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) on polar.synack.me
X-Spam-Level: 
X-Spam-Status: No, score=-1.3 required=5.0 tests=BAYES_00,INVALID_MSGID
	autolearn=no autolearn_force=no version=3.4.4
X-Google-Language: ENGLISH,ASCII-7-bit
X-Google-Thread: 103376,9c86eb13dd395066
X-Google-Attributes: gid103376,public
From: dewar@merv.cs.nyu.edu (Robert Dewar)
Subject: Re: CRC in Ada?
Date: 1997/03/08
Message-ID: <dewar.857828494@merv>#1/1
X-Deja-AN: 223977391
References: <1997Mar2.220652@nova.wright.edu> <1997Mar5.131846.1@eisner>
 <5fmo1k$adm@mulga.cs.mu.OZ.AU> <1997Mar6.114441.1@eisner>
 <E6n850.3Ct@world.std.com> <1997Mar7.090814.1@eisner> <33206340.2616@bix.com>
 <1997Mar7.202252.1@eisner>
Organization: New York University
Newsgroups: comp.lang.ada
Date: 1997-03-08T00:00:00+00:00
List-Id: <comp.lang.ada>


Larry says

<<As for a C implementation being better than an Ada implementation
at single character reads, I imagine there must be another language
characteristics where Ada has some advantage or other.>>

The comparison between C and Ada here is apples-oranges. Text_IO.Get
has far more elaborate semantics than getchar, so you cannot compare
the two. This is a common effect (see another example below). If you
want the simple minded semantics of getchar, then this is trivially
programmed in Ada (the GNAT package GNAT.IO is a much closer approximation
to the C level semantics).

Another interesting case of this is a timing comparison that Bob Klungle
sent me comparing the use of the official log and the log in the
"secret" package Aux. The log in Aux is a direct call to C, the log
in Ada has rather different semantics, as you can see from its coding:

   function Log (X : Float_Type'Base) return Float_Type'Base is
   begin
      if X < 0.0 then
         raise Argument_Error;

      elsif X = 0.0 then
         raise Constraint_Error;

      elsif X = 1.0 then
         return 0.0;
      end if;

      return Float_Type'Base (Aux.Log (Double (X)));
   end Log;

Those extra tests, required by Ada semantics, end up making the use of
the Ada log function very much slower (almost a factor of two in Bob's tests)
which is a bit worrisome -- safety and accuracy are not free :-)