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sub SaveFirstSeven()                                                            # Save the first 7 parameter registers
 {Push rax;
  Push rdi;
  Push rsi;
  Push rdx;
  Push r10;
  Push r8;
  Push r9;
  7 * RegisterSize(rax);                                                        # Space occupied by push
 }

sub RestoreFirstSeven()                                                         # Restore the first 7 parameter registers
 {Pop r9;
  Pop r8;
  Pop r10;
  Pop rdx;
  Pop rsi;
  Pop rdi;
  Pop rax;
 }

sub RestoreFirstSevenExceptRax()                                                # Restore the first 7 parameter registers except rax which is being used to return the result
 {Pop r9;
  Pop r8;
  Pop r10;
  Pop rdx;
  Pop rsi;
  Pop rdi;
  Add rsp, RegisterSize(rax);                                                   # Skip rax
 }

sub RestoreFirstSevenExceptRaxAndRdi()                                          # Restore the first 7 parameter registers except rax and rdi which are being used to return the results
 {Pop r9;
  Pop r8;
  Pop r10;
  Pop rdx;
  Pop rsi;
  Add rsp, 2*RegisterSize(rax);                                                 # Skip rdi and rax
 }

sub RegisterSize($)                                                             # Return the size of a register
 {my ($r) = @_;                                                                 # Register
  return 16 if $r =~ m(\Ax);
  return 32 if $r =~ m(\Ay);
  return 64 if $r =~ m(\Az);
  8
 }

sub ClearRegisters(@)                                                           # Clear registers by setting them to zero
 {my (@registers) = @_;                                                         # Registers
  @_ == 1 or confess;
  for my $r(@registers)
   {my $size = RegisterSize $r;
    Xor    $r, $r if $size == 8;
    Vpxorq $r, $r if $size  > 8;
   }
 }

#D1 Structured Programming                                                      # Structured programming constructs

sub If(&;&)                                                                     # If
 {my ($then, $else) = @_;                                                       # Then - required , else - optional
  @_ >= 1 or confess;
  if (@_ == 1)                                                                  # No else
   {Comment "if then";
    my $end = Label;
    Jz $end;
    &$then;
    SetLabel $end;
   }
  else                                                                          # With else
   {Comment "if then else";
    my $endIf     = Label;
    my $startElse = Label;
    Jz $startElse;
    &$then;
    Jmp $endIf;
    SetLabel $startElse;
    &$else;
    SetLabel  $endIf;
   }
 }

sub For(&$$$)                                                                   # For
 {my ($body, $register, $limit, $increment) = @_;                               # Body, register, limit on loop, increment
  @_ == 4 or confess;
  Comment "For $register $limit";
  my $start = Label;
  my $end   = Label;
  SetLabel $start;
  Cmp $register, $limit;
  Jge $end;

  &$body;

  if ($increment == 1)
   {Inc $register;
   }
  else
   {Add $register, $increment;
   }
  Jmp $start;
  SetLabel $end;
 }

sub S(&%)                                                                       # Create a sub with optional parameters name=> the name of the subroutine so it can be reused rather than regenerated, comment=> a comment describing the sub
 {my ($body, %options) = @_;                                                    # Body, options.
  @_ >= 1 or confess;
  my $name    = $options{name};                                                 # Optional name for subroutine reuse
  my $comment = $options{comment};                                              # Optional comment
  Comment "Subroutine " .($comment//'');

  if ($name and my $n = $subroutines{$name}) {return $n}                        # Return the label of a pre-existing copy of the code

  my $start = Label;
  my $end   = Label;
  Jmp $end;
  SetLabel $start;
  &$body;
  Ret;
  SetLabel $end;