🚀 go-pugleaf

/* When Microsoft C 6.0 compiles the following simple program 
   the compiler gets confused in constructing the comparisons
   for the 32-bit switch/case statements.  It appears to use
   the fact that B1, B2, and B3 all have the same value in the
   high 16-bits, leading potentially to shorter faster code,
   but it loses track of the logic/branching thread by subtracting
   values from 'dx' rather than comparing.  Compile with /Fc
   Replacing the switch/case with if() statements leads to correct
   execution.
   
   The program gives the following results:
   
      for A1 expected 0 got 0
      for A2 expected 1 got 1
      for A3 expected 2 got 2
      for B1 expected 2 got 2
      for B2 expected 1 got 3
      for B3 expected 0 got 3

   ------------------------
      
   David L. Huestis
   SRI International
   <huestis@mplvax.sri.com>

   --------------------------------------------------------------------
*/

#include <stdio.h>

#define A1 0x0A0001UL
#define A2 0x0A0002UL
#define A3 0x0A0003UL
#define B1 0x0B0001UL
#define B2 0x0B0002UL
#define B3 0x0B0003UL

int tsw(unsigned long sw)
{
      switch(sw)
        {
          case A1 : case B3 :
            return( 0 ) ;
            break ;
          case A2 : case B2 :
            return( 1 ) ;
            break ;
          case A3 : case B1 :
            return( 2 ) ;
            break ;
            
          default :
            break ;
        }
      return(3) ;
}

main()
{
      printf("for A1 expected 0 got %d\n", tsw(A1) ) ;
      printf("for A2 expected 1 got %d\n", tsw(A2) ) ;
      printf("for A3 expected 2 got %d\n", tsw(A3) ) ;
      printf("for B1 expected 2 got %d\n", tsw(B1) ) ;
      printf("for B2 expected 1 got %d\n", tsw(B2) ) ;
      printf("for B3 expected 0 got %d\n", tsw(B3) ) ;
}