1   
2   // Since this is Assembly Language code for Delphi, you need
3   //  a version (such as Enterprise) that supports compiling it.
4   
5   // NOTE: ByteBool, WordBool, and LongBool should be typecast
6   //  to Boolean when calling this function
7   // Example:  IntegerValue := B2I(Boolean(WB)); (cast of WordBool type)
8   
9   
10  // convert True or False to guaranteed 1 or 0
11  function B2I(b: Boolean): Integer;
12  // This block is how you might ordinarily do this in Delphi,
13  //  especially if you don't have a version that supports Assembly:
14  //begin          // recall that numerically, any nonzero value is True
15  //  Result := ORD(b <> False);
16  //end;
17  // But: the above code compiles to 8 bytes...
18  
19  
20  //Efficient Assembly Code (6 bytes):
21  // When the B2I() function begins, the Boolean value
22  //  from parameter  b  is in Register  al
23  //  and a zero is False; any other value can be True
24    asm
25      neg    al
26  // negation of any nonzero value will set the Carry Flag
27      sbb    eax, eax
28  // subtraction of itself (with borrow) yields 0 (or -1 if Carry set)
29      neg    eax
30  // negation now yields only one nonzero value (-1 becomes 1)
31    end;
32  // When this funcion ends, Register  eax  holds the Result value
33  
34  //NOTE: this function was developed because InterBase does
35  // not support Boolean data.  So, in converting a Paradox
36  // database to InterBase, it is convenient for existing boolean
37  // variables to remain the same, so long as when passed to the
38  // database, they are converted using B2I().  Note that converting
39  // them from 0 or 1 to true or false, when pulling the data back
40  // from InterBase integer form, is almost trivially easy:
41  
42  //BoolVar := (FieldByName('IntField').AsInteger <> 0);
43  
44  //Final note: for long-term portability, it is always best to
45  // compare a boolean value with False instead of True.
46  // That is:
47  //   if (BoolVar = False) then
48  // or
49  //   if (BoolVar <> False) then
50  // is better than 
51  //   if (BoolVar = True) then
52  // or
53  //   if (BoolVar <> True)
54  //The reason is because False is always exactly one value: zero
55  // while True may be any nonzero value in Delphi.  In porting a
56  // comparison of True, you cannot be certain that the ported
57  // comparison will work properly (True may have a particular
58  // value in the destination environment).