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Q61434: XOR, OR, AND Convert Floating Point to Integer

Article: Q61434
Product(s): See article
Version(s): 4.00 4.00b 4.50
Operating System(s): MS-DOS
Keyword(s): ENDUSER | SR# S900424-129 B_BasicCom | mspl13_basic
Last Modified: 1-MAY-1990

The BASIC bitwise operators (AND, OR, XOR, and NOT) do not operate
directly on floating-point numbers (SINGLE ! or DOUBLE #) or string
variables ($). They also do not operate directly on currency data type
numbers (@) in Microsoft BASIC Professional Development System (PDS)
version 7.00. When a bitwise operation is attempted with a
floating-point variable that has a value greater than the maximum LONG
integer (2,147,483,647), an "Overflow" error occurs.

To properly perform a bitwise operation on a floating-point variable,
the floating-point number must be moved into a LONG using a bitwise
move. Two functions are listed below to move between SINGLEs and LONGs
so that bitwise operations can be used on SINGLE floating-point
numbers.

This information applies to Microsoft QuickBASIC versions 4.00, 4.00b,
and 4.50, and Microsoft BASIC Compiler versions 6.00 and 6.00b for
MS-DOS and MS OS/2, and Microsoft BASIC PDS version 7.00 for MS-DOS
and MS OS/2.

When a bitwise operation is attempted on a floating point or currency
numeric type, the fractional number is converted to its INTEGER or
LONG equivalent and the operation is then performed using INTEGERs or
LONGs. This can cause an "Overflow" error message if the value of the
floating-point number exceeds the maximum value of a LONG integer.

Another method of performing bitwise operations on a floating-point
number is to convert the number to a LONG, manipulate the bits, and
then convert it back to a floating-point number. The code example
below demonstrates moving between SINGLEs and LONGs using the MKS$,
MKL$, CVS, and CVL functions. Converting DOUBLEs is more involved
because they are longer than any integer type. A similar operation
could be performed to convert DOUBLEs using two LONGs and the MKD$ and
CVD functions as well.

Code Example
------------

The following code example performs a bitwise move by using the MKS$,
MKL$, CVS, and CVL functions using a string as an intermediary:

'Module level demonstrates using functions
s! = 1.0
t! = 1.1
l& = SingleToLong(s!)
m& = SingleToLong(t!)
n& = l& XOR m&                    'Bit AND (won't work with SINGLEs)
PRINT HEX$(l&), HEX$(m&), HEX$(n&)'3F800000   3F8CCCCD   3F800000
u! = LongToSingle(n&)             'Equivalent of bit AND of s! and
                                  't!
PRINT u!                          '1.75495E-39
END

FUNCTION SingleToLong&(s!)
  SingleToLong& = CVL(MKS$(s!))
END FUNCTION

FUNCTION LongToSingle!(l&)
  LongToSingle! = CVS(MKL$(l&))
END FUNCTION

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