Article ID: 111234
Article Last Modified on 10/17/2003
APPLIES TO
- Microsoft FORTRAN PowerStation 1.0 Standard Edition
- Microsoft Fortran PowerStation 1.0a for MS-DOS
- Microsoft FORTRAN PowerStation 32
This article was previously published under Q111234
SYMPTOMS
The ISHL and ISHFT intrinsic functions may return incorrect results when shifting INTEGER*1 or INTEGER*2 variables. The incorrect results occur only when right-shifting negative values.
CAUSE
The compiler converts the value to be shifted to a 4-byte value. For 1- and 2-byte negative integers, the higher order bits are filled with 1s, which can be incorrectly shifted into the low order bytes.
RESOLUTION
Convert the bit pattern of the negative INTEGER*1 or INTEGER*2 value to an unsigned INTEGER*4 value. This is done by adding 256 to a negative INTEGER*1 value or by adding 65536 to a negative INTEGER*2 value. Then shift the resulting INTEGER*4 value.
STATUS
Microsoft has confirmed this to be a problem in FORTRAN PowerStation 32 for Windows NT version 1.0 and MS-DOS version 1.0 and 1.0a. This problem was fixed in FORTRAN PowerStation 32, version 4.0.
MORE INFORMATION
The following sample illustrates the problem:
Sample Code #1
c Compile options needed: none
c
integer*2 i2
integer*1 i1
i1 = -123
i2 = i1
write(*,'('' Before shift '',Z2,2x,z4)') i1, i2
write(*,'('' After shift '',Z2,2x,z4)') ishl(i1,-2), ishl(i2,-2)
end
Output
Before shift 85 FF85
After shift E1 FFE1
The following code illustrates the article's resolution:
Sample Code #2
c Compile options needed: none
c
integer*4 j,k
integer*2 i2
integer*1 i1
i1 = -123
i2 = i1
j = 256 + i1
k = 65536 + i2
write(*,'('' Before shift '',Z2,2x,z4)') i1, i2
write(*,'('' After shift '',Z2,2x,z4)') ishl(j,-2), ishl(k,-2)
end
Output
Before shift 85 FF85
After shift 21 3FE1
Additional query words: 1.00
Keywords: kbbug kbfix kblangfortran KB111234
