FIX: F6099 w/ IAND in an IF Compiled w/ /4Yb and /Od

MS-DOS                   | OS/2

The information in this article applies to:

• Microsoft FORTRAN for MS-DOS, versions 4.0, 4.01, 4.1, 5.0, and 5.1
• Microsoft FORTRAN for OS/2, versions 4.1, 5.0, and 5.1

SYMPTOMS

Programs compiled with the /4Yb (or the $DEBUG metacommand) and /Od switches in Microsoft FORTRAN versions 4.0, 4.01, 4.1, 5.0, and 5.1 under MS-DOS and versions 4.1, 5.0, and 5.1 under OS/2 and that contain an IAND function within an IF statement may incorrectly generate the following error:

   Run-Time Error F6099: $DEBUG
        INTEGER overflow

CAUSE

The F6099 error occurs for constants less than 255 because the /4Yb compiler option (or the $DEBUG metacommand) causes the compiler to generate code for checking integer overflow in which an incorrect comparison is made on the low word of the variable stored in the AX register. A constant greater than 255 in the IAND function forces a comparison on the high word of the register, avoiding the generation of the incorrect overflow error.

RESOLUTION

To avoid this error, compile either without the /4Yb (or the $DEBUG metacommand) or the /Od compiler option.

STATUS

Microsoft has confirmed this to be a problem in FORTRAN versions 4.0, 4.01, 4.1, 5.0, and 5.1. This problem was corrected in FORTRAN PowerStation, version 1.0.

MORE INFORMATION

The following code can be used to reproduce the problem.

Sample Code 1

C Compile options needed: /Od

$debug

      integer*4 k
      k=32768
      if (iand(k, 1) .ne. 0) write(*, *) 'Not Equal to Zero'
      end