12 bytes LongReal type - Gpc

8 Apr 2001


      {
For those who want to understand the structure of the double extended
format, here is a little program which may be helpful :
(I'll appreciate comments to improve it)
--
Â«CouperinÂ»
}
Program Lr2Scr;
{  ----------------------------------------------------------------------
         What is Intel IEEE Double-Extended format (12 bytes) ?
                  "Couperin" f.couperin@online.fr
   ----------------------------------------------------------------------  }
Const
  LongRealSize = 12;
Type
  T_LongRealBis = Packed Array [1..LongRealSize] Of Byte;
  String2 = String(2);
  String11 = String(11);
  String16 = String(16);
  String27 = String(27);
  Int16 = Integer(16);
  Word16 = Word(16);
  Word64 = Word(64);
Var
  A : LongReal;
  Abis : T_LongRealBis Absolute A;
Function Byte2Hex(X : Byte): String2;
  Const
    Hexa : Array [0..15] Of Char = '0123456789ABCDEF';
  Begin
    Byte2Hex := Hexa[X Shr 4] + Hexa[X And 15]
  End;
Function ExtractE(X : T_LongRealBis): Word16;
  Var
    E : Word16;
  Begin
    E := X[10] And 2#01111111;
    ExtractE := (E Shl 8) + X[9]
  End;
Function F2Hex(X : T_LongRealBis): String16;
  Var
    S : String16 = '';
    I : Byte;
  Begin
    For I := 8 DownTo 2 Do S := S + Byte2Hex((X[I] Shl 1) + (X[I-1] Shr 7));
    S := S + Byte2Hex(X[1] Shl 1);
    F2Hex := S
  End;
Function Exponent(X : T_LongRealBis): Int16;
  Var
    E : Word16;
  Begin
    E := ((X[10] And 2#01111111) Shl 8) + X[9];
    If E = 0
      Then Exponent := -16382
      Else Exponent := E - 16383
  End;
Function Int2String(X:Integer):String11;
  Var
    S:String11;
  Begin
    Str(X,S);
    Int2String := S
  End;
Function LR2HexFloat(X : T_LongRealBis): String27;
  Var
    S : String27 = '$';
  Begin
    If (Abis[10] And 2#10000000) > 0 {sign}
      Then S := S + '-'
      Else S := S + '+';
    If (Abis[8] And 2#10000000) > 0 {explicit leading significand bit}
      Then S := S + '1.'
      Else S := S + '0.';
    LR2HexFloat := S + F2Hex(X) + 'p' + Int2String(Exponent(X))
  End;
Procedure DisplayA;
  Var
    N : Byte;
  Begin
    Writeln(A:28,' = ');
    Writeln(LR2HexFloat(Abis),' ("Hex Float") = ');
    For N := LongRealSize DownTo 1 Do Write(Byte2Hex(Abis[N]));
    Writeln(' (internal representation)');
    Write('s (sign) = ');
    Writeln(Ord((Abis[10] And 2#10000000) > 0));
    Write('e (biased exponent) = ',ExtractE(Abis));
    Writeln(' (e - 16383 = ',ExtractE(Abis) - 16383,')');
    Write('j (explicit leading significand bit) = ');
    Writeln(Ord((Abis[8] And 2#10000000) > 0));
    Write('f (fraction) = 16#',F2Hex(Abis));
    Writeln
  End;
Begin
  Writeln('Size of the LongReal type (in Bytes) : ',SizeOf(LongReal));
  If LongRealSize <> SizeOf(LongReal)
    Then Writeln('Sorry, this LongReal format (Size : ',SizeOf(LongReal),
                 ') is unknown to this program.')
    Else
      Begin
        {$ifdef __BYTES_BIG_ENDIAN__} {Is this really useful ?}
        Writeln('Big endian format.'#10#13,
                'Sorry, this program is made for the little endian format.')
        {$else}
        Writeln('Little endian format');
        Repeat
          Writeln;
          Writeln('Enter a real number (0 to Quit)');
          Readln(A);
          Writeln;
          DisplayA;
        Until A = 0
        {$endif}
      End
End.