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Pascal

This month I thought of doing something simple. I thought I would explain how to call an assembler routine in Pascal. All the code in listing 1 does is check to see if the user has a 386 or higher machine.

Pascal includes a very nice "directive" called 'assembler' that you add to the end of a function or procedure declaration line.

function funcname: boolean; assembler;

This tells the pascal compiler that the following function is an assembler routine. When this happens, the compiler creates a few optimizer options and makes your code smaller and faster.

I won't get in to detail on how the assembler routine works, but I will show how you create the assembler function.

Create a procedure/function just like normal, except add the assembler; "directive" on to it. Then instead of using begin/end; use asm/end;.

In a function, AX is returned as the function value. In a boolean; typed function, AX is returned True (Not zero), or False (is zero). If you want to return a 32 bit value, use DX:AX. ¥

Listing 1

program Is386demo;
uses dos;

function is386: boolean; assembler;
  asm
    push bx        { save reg's used (except ax)     }
    xor  ax,ax     { assume false                    }
    mov  bx,7000h  { if bits 12,13,14 are still set  }
    push bx        { after pushing/poping to/from    }
    popf           { the flags register then we have }
    pushf          { a 386+                          }
    pop  bx
    and  bx,7000h
    cmp  bx,7000h
    jne  @Not386
    mov  ax,-1
@Not386:
    pop  bx        { restore register                }
end;

begin
   if not is386 then
     writeln('You have a 286 or before')
   else
     writeln('You have a 386 or higher (32-bits)');
end.

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