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Message-ID: <8706041655.AA23291@ucbvax.Berkeley.EDU>
Date: Thu, 4-Jun-87 12:21:00 EDT
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Posted: Thu Jun  4 12:21:00 1987
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DEC Ada Problem Report
from:  Mr. Gary Sivak  (513) 255-3586
ASD/ENASF
wright-Patterson Air Force Base, Ohio 45433-6503
     There seems to be a problem with the way the VAX-hosted DEC-Ada
compiler V1.3-24 handles SHORT_INTEGER variables.
     Explanation.  In VAX Ada, the SHORT_INTEGER is defined as a 16-bit
two's complement number with the sign bit, in the left-most position,
set to 1 for negative values.  For example, for 3-bit arithmetic we have:
NUMERIC_VALUE	BIT_REPRESENTATION
-4		100
-3		101
-2		110
-1		111
0		000
1		001
2		010
3		011
     The valid range of two's complement 3-bit numbers is thus -4 through +3.
Similarly, the range of 16-bit two's complement numbers is -32,768 through
+32,767.
     Problem.  One can store the minimum value -32,768 into a
SHORT_INTEGER variable with a GET instantiated for SHORT_INTEGER, but
you cannot do it Via an assignment statement.  The exception
NUMERIC_ERROR is raised when you try. The minimal value an assignment
statement will accept is -32,767. 
     The following simple source code and test results demonstrate the problem:


with TEXT_IO; use TEXT_IO;
with SHORT_INTEGER_TEXT_IO; use SHORT_INTEGER_TEXT_IO;
procedure TEST_READ is
   INPUT_VALUE : SHORT_INTEGER;
begin --TEST_READ
   loop
      PUT("Enter INPUT_VALUE. ");
      GET(INPUT_VALUE);
      NEW_LINE;
      PUT(INPUT_VALUE);
      NEW_LINE;
   end loop;
end TEST_READ;
RUN TEST_READ
Enter INPUT_VALUE. 32767
 32767
Enter INPUT_VALUE. -32767

-32767
Enter INPUT_VALUE. -32768

-32768
Enter INPUT_VALUE. 
*INTERRUPT*

with TEXT_IO; use TEXT_IO;
with SHORT_INTEGER_TEXT_IO; use SHORT_INTEGER_TEXT_IO;

procedure TEST_ASSIGN is
   INPUT_VALUE : SHORT_INTEGER;
begin --TEST_ASSIGN
   INPUT_VALUE := -32768;
   NEW_LINE;
   PUT(INPUT_VALUE);
   NEW_LINE;
end TEST_ASSIGN;
$ RUN TEST_ASSIGN
%ADA-I-NUMERIC_ERROR, NUMERIC_ERROR
%SYSTEM-F-INTDIV, arithmetic trap, integer divide by zero at PC=00000848, 
PSL=03C000A6
%TRACE-E-TRACEBACK, symbolic stack dump follows
module name     routine name                     line       rel PC    abs PC
                                                           0000D1D6  0000D1D6
----- above condition handler called with exception 00000484:
%SYSTEM-F-INTDIV, arithmetic trap, integer divide by zero at PC=00000848, 
PSL=03C000A6
----- end of exception message
TEST_ASSIGN     TEST_ASSIGN                         7      00000012  00000848
ADA$ELAB_TEST_A ADA$ELAB_TEST_ASSIGN                       00000009  00000609
                                                           000008D9  000008D9
                                                           0000CFD2  0000CFD2
ADA$ELAB_TEST_A ADA$ELAB_TEST_ASSIGN                       0000001B  0000061B
                                                           000008B4  000008B4
     if anyone knows why you can get but not assign, please let me know.
                                        gary Sivak

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