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Q60747: Quick Compiler Incorrectly Zero-Extends Ones Complement

Article: Q60747
Product(s): See article
Version(s): 6.00   | 6.00
Operating System(s): MS-DOS | OS/2
Keyword(s): ENDUSER | buglist6.00 s_quickc | mspl13_c
Last Modified: 19-APR-1990

The C Version 6.00 quick compiler incorrectly zero-extends ones
complement operations that result in negative integers, rather than
sign-extending them. The QuickC (QC) 2.50 compiler works correctly.

When compiled with the quick compiler, the following sample code
produces a value of 64512 for l. When compiled with the full
optimizing compiler, the correct result of -1024 is produced for l.
This is a problem with QCL, not CL.

In ANSI C, the constant 1023 is represented as an integer. The
ones complement of 1023 (-1024) should remain an integer and when
promoted to a long, this integer should then be sign-extended
preserving the value. QCL correctly stores 1023 as an integer;
however, it doesn't sign-extend the ones complement as it should.

One solution is to typecast the ones complement to an int before
assigning it to a long [for example, l=(int)~1023].

Microsoft has confirmed this to be a problem with Version 6.00. We are
researching this problem and will post new information here as it
becomes available.

Sample Code
-----------

#include<stdio.h>

void main(void)
{
  long l;

  l=~1023;  /* Ones complement not properly extended */

  printf("%ld\n",l);
}

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