[Bug report] 12 bytes LongReal - Gpc

8 Apr 2001


      Sorry, I discovered a serious bug.
The two smallest subnormal numbers (of 12 bytes LongReal type) cannot be
written ; the program hangs and can't be stopped with CTRL+C. :-(
(gpc version 20010331, based on 2.95.2 19991024 (release)
Machine : Intel Pentium 120 + Windows 98)
The first program allows to understand what is happening.
The second one is the shorter I can write.
--
Â«CouperinÂ»
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
Program LRBug1;
{  ----------------------------------------------------------------------
   BUG ! Intel IEEE Double-Extended (12 bytes) real numbers :
   The two smallest subnormal numbers cannot be written to the screen...
   The program hangs after : 1.000000000000001e-4950 (three steps above 0)
   ----------------------------------------------------------------------  }
Const
  LongRealSize = 12;
Type
  T_LongRealBis = Packed Array [1..LongRealSize] Of Byte;
  String2 = String(2);
Var
  A : LongReal;
  Abis : T_LongRealBis Absolute A; {to read the binary content of A}
  I,N : Byte;
Function Byte2Hex(X : Byte): String2;
  Const
    Hexa : Array [0..15] Of Char = '0123456789ABCDEF';
  Begin
    Byte2Hex := Hexa[X Shr 4] + Hexa[X And 15]
  End;
Begin
  If LongRealSize <> SizeOf(LongReal)
    Then
      Begin
        Writeln('This LongReal format (',SizeOf(LongReal),
          ') is unknown to this program.');
      End
    Else
      Begin
        A := 3.3621031431120935120e-4932; {biggest subnormal number}
        For I := 0 To 64 Do
          Begin
            Write('16#');
            {$ifdef __BYTES_BIG_ENDIAN__}
            For N := 1 To LongRealSize Do Write(Byte2Hex(Abis[N]));
            {$else}
            For N := LongRealSize DownTo 1 Do Write(Byte2Hex(Abis[N]));
            {$endif}
            Writeln(' is the representation of ',A);
            Writeln;
            A := A/2;
          End;
        Writeln;
        Writeln('OK')
    End
End.
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
Program LRBug2;
Var
  A : LongReal;
  I : Byte;
Begin
  A := 3.3621031431120935120e-4932; {biggest subnormal number}
  For I := 0 To 64 Do
    Begin
      Writeln(A);
    End;
  Writeln('OK')
End.