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program Main;
const TAB = ^I;
var Look : char;
procedure Error(s : string);
begin
WriteLn;
WriteLn(^G, 'Error: ', s, '.');
end;
procedure GetChar;
begin
Read(Look);
end;
procedure Abort(s : string);
begin
Error(s);
Halt;
end;
procedure Expected(s : string);
begin
Abort(s + ' expected');
end;
procedure Match(c : char);
begin
if c = Look then GetChar
else Expected('''' + c + '''');
end;
function IsAlpha(c : char) : boolean;
begin
IsAlpha := upcase(c) in ['A'..'Z'];
end;
function IsDigit(c : char) : boolean;
begin
IsDigit := c in ['0'..'9'];
end;
function GetName : char;
begin
if not IsAlpha(Look) then Expected('Name');
GetName := UpCase(Look);
GetChar;
end;
function GetNum : char;
begin
if not IsDigit(Look) then Expected('Integer');
GetNum := Look;
GetChar;
end;
procedure Emit(s : string);
begin
Write(TAB, s);
end;
procedure EmitLn(s : string);
begin
Emit(s);
WriteLn;
end;
procedure EmitLabel(s : string);
begin;
WriteLn(s+':');
end;
procedure Expression; Forward;
procedure Factor;
begin
if Look = '(' then begin
Match('(');
Expression;
Match(')');
end
else
EmitLn('mov eax, ' + GetNum);
end;
procedure Multiply;
begin
Match('*');
Factor;
EmitLn('pop ebx');
EmitLn('mul ebx');
end;
procedure Divide;
begin
Match('/');
Factor;
EmitLn('pop ebx');
EmitLn('div ebx');
end;
procedure Term;
begin
Factor;
while Look in ['*', '/'] do
begin
EmitLn('push eax');
case Look of
'*': Multiply;
'/': Divide;
else Expected('* or /');
end;
end;
end;
procedure Add;
begin;
Match('+');
Term;
Emitln('pop ebx');
EmitLn('add eax, ebx');
end;
procedure Subtract;
begin;
Match('-');
Term;
EmitLn('pop ebx');
EmitLn('sub eax, ebx');
end;
procedure Expression;
begin
Term;
while Look in ['+', '-'] do
begin
EmitLn('push eax');
case Look of
'+': Add;
'-': Subtract;
else Expected('+ or -');
end;
end;
end;
procedure Init;
begin
GetChar;
end;
procedure Prologue;
begin
WriteLn('[bits 32]');
WriteLn('section .text');
WriteLn('global main');
EmitLabel('main');
EmitLn('push ebp');
EmitLn('mov ebp, esp');
end;
procedure Epilogue;
begin
EmitLn('leave');
EmitLn('ret');
end;
begin
Prologue;
Init;
Expression;
Epilogue;
end.
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