Re: FORTRAN bug(was Re: C++ vs. Ada -- Is Ada loosing?)

[noc.near.net!inmet!spock!stt@uunet.uu.net (Tucker Taft)]

In article <19921211.142820.329@almaden.ibm.com> 
  jnestoriak@vnet.ibm.com (John Nestoriak III) writes:

>In <1992Dec11.210404.2480@inmet.camb.inmet.com> Tucker Taft writes:

>>One of our goals for Ada 9X has been to give system programmers
>>back this feeling of satisfaction, so that you can do "code generation
>>in your head" for most Ada constructs.  In other words,
>>you can predict about how many machine instructions (and
>>generally which ones ;-) will be generated for each
>>construct in your program.  For a real-time embedded language,
>>this seems particulary important.
>
>Are there plans to add bitwise operations to Ada 9X?  Lack of
>built in shift operators was a disappointing discovery for me.
>I know that Ada is a high order language and therefor less suitable
>for manipulating bits than say C, but there are high level functions
>that need to manipulate bits.  I'm thinking in particular of
>compression routines.  The project I work on is Ada but we had to
>implement compression using C.

Yes.  We are planning to add "modular types" to Ada 9X,
which are unsigned, wrap-around types with a user-specified
modulus (normally a power-of-2).  These types will have +/-, etc., 
bit-wise and, or, xor, and not, as well as a language-defined
generic package that provides shift operations.  This
package is intended to be recognized by the compiler, so
that these shift operations result in inline machine instructions for
shifting.

Here is the tentative syntax:

   type Unsigned_16 is mod 2**16;  -- declare a 16-bit unsigned type

   package Shift_16 is new System.Shifts(Unsigned_16); use Shift_16;
                                   -- Get the shift functions
   X : Unsigned_16 := 16#00FF#;
   Y, Z : Unsigned_16;
begin
   Y := Left_Shift(X, 5);          -- Try them out
   Z := X and Y;
   if Z /= 16#00E0# then
       Put_Line("Send the 9X compiler back"); -- ;-)

etc...

S. Tucker Taft  stt@inmet.com
Ada 9X Mapping/Revision Team
Intermetrics, Inc.
Cambridge, MA  02138