Asm/fi

program asmDemo(input, output, stderr);

// The $asmMode directive informs the compiler
// which syntax is used in asm-blocks.
// Alternatives are 'att' (AT&T syntax) and 'direct'.
{$asmMode intel}

var
    n, m: longint;
begin
    n := 42;
    m := -7;
    writeLn('n = ', n, '; m = ', m);
    
    // instead of declaring another temporary variable
    // and writing "tmp := n; n := m; m := tmp;":
    asm// eax := n// xchg can only operate at most on one memory address// swaps values in eax and at m// n := eax (holding the former m value)// an array of strings after the asm-block closing 'end'// tells the compiler which registers have changed// (you don't wanna mess with the compiler's notion// which registers mean what)
        mov eax, n  // eax := n
        // xchg can only operate at most on one memory address
        xchg eax, m // swaps values in eax and at m
        mov n, eax  // n := eax (holding the former m value)
    // an array of strings after the asm-block closing 'end'
    // tells the compiler which registers have changed
    // (you don't wanna mess with the compiler's notion
    // which registers mean what)
    END ['eax'];
    
    writeLn('n = ', n, '; m = ', m);
end.

program sign(input, output, stderr);

type
    signumCodomain = -1..1;

{ returns the sign of an integer }
function signum(const x: longint): signumCodomain;
{$ifdef CPUx86_64} // ============= optimized implementation
assembler;
{$asmMode intel}
asm// load constants: cmov cannot handle immediates// xor-instruction modifies flags => put it prior test// r8 := 0// comparison pulled up front for pipelining// x = 0 ?// load constants, since cmov cannot handle immediates// r9 := -1// determine result// result := 1// if x < 0 then result := -1// if x = 0 then result := 0
    // load constants: cmov cannot handle immediates
    // xor-instruction modifies flags => put it prior test
    xor   r8,  r8 // r8 := 0
    
    // comparison pulled up front for pipelining
    test  x,   x  // x = 0 ?
    
    // load constants, since cmov cannot handle immediates
    mov   r9, -1  // r9 := -1
    
    // determine result
    mov   eax, 1  // result := 1
    cmovl eax, r9 // if x < 0 then result := -1
    cmove eax, r8 // if x = 0 then result := 0
END;
{$else} // ========================== default implementation
begin
    // This is what virtually math.sign does.
    // The compiled code requires _two_ cmp instructions, though. 
    if x > 0 then
    begin
        signum := 1;
    end
    else if x < 0 then
    begin
        signum := -1;
    end
    else
    begin
        signum := 0;
    end;
end;
{$endif}

// M A I N =================================================
var
    x: longint;
begin
    readLn(x);
    writeLn(signum(x));
end.