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From: tedg@apollo.HP.COM (Ted Grzesik)
Newsgroups: comp.lang.ada
Subject: float constraint checks
Message-ID: <1991Jun12.190054.27094@apollo.hp.com>
Date: 12 Jun 91 19:00:54 GMT
Sender: netnews@apollo.hp.com (USENET posting account)
Organization: Hewlett-Packard Company, Chelmsford, MA
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List-Id: <comp.lang.ada>

I have a question regarding constraint checks of floating point assignments.

The LRM (3.5.7) does not make it clear to me whether my compiler is failing to give a CONSTRAINT_ERROR in the following situation:

Note: some code not shown.


with text_io;

procedure float_test is

   package short_float_io is new text_io.float_io ( short_float );
   package long_float_io is new text_io.float_io (float );
   package int_io is new text_io.integer_io (integer);
 
   value,  value1,  value2   : short_float;
   lvalue, lvalue1, lvalue2  : float;

   begin
       .
       .
       .

     value := short_float(-9.0E-150);
     text_io.put( "The value of -9.0E-150 is " );
     short_float_io.put ( value );
     text_io.new_line;

     value  := short_float(-9.0E-38);
     value1 :=  short_float(9.0E-38);
     value2 :=  value * value1;
     text_io.put ( "The value of -9.0E-37 * 9.0E-37 is ");
     short_float_io.put( value2 );
     text_io.new_line;

     lvalue  := float(-9.0E-500);
     text_io.put ( " The value of -9.0E-500 is " );
     long_float_io.put ( lvalue );
     text_io.new_line;

     lvalue  := float(-9.0E-500);
     lvalue1 :=  float(9.0E-500);
     lvalue2 :=  lvalue * lvalue1;
     text_io.put ( " The value of -9.0E-500 * -9.0E-500 is " );
     long_float_io.put( lvalue2 );
     text_io.new_line;

   end float_test;

Execution results:

Attributes for short_float:
DIGITS:           6
MANTISSA:          21
EPSILON:  9.53674316406250E-07
EMAX:          84
SMALL:  2.58493941422821E-26
LARGE:  1.93428038904620E+25
SAFE_EMAX:         126
SAFE_SMALL:  5.87747175411144E-39
SAFE_LARGE:  8.50705511654154E+37
Attributes for float:
DIGITS:          15
MANTISSA:          51
EPSILON:  8.88178419700125E-16
EMAX:         204
SMALL:  1.94469227433161E-62
LARGE:  2.57110087081438E+61
SAFE_EMAX:        1022
SAFE_SMALL:  1.11253692925360E-308
SAFE_LARGE:  4.49423283715579E+307
The value of -9.0E-150 is  0.00000E+00
The value of -9.0E-37 * 9.0E-37 is  0.00000E+00
 The value of -9.0E-500 is  0.00000000000000E+00
 The value of -9.0E-500 * -9.0E-500 is  0.00000000000000E+00

-- 
Ted Grzesik       Massachusetts Language Lab             Hewlett-Packard Company
tedg@apollo.hp.com                          Chelmsford, MA  (508) 256-6600 x5959
"Civilization is the limitless multiplication of unnecessary necessities."
                                       -- Mark Twain (Samuel Clemens)