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program Main;
const
TAB = ^I;
LF = ^J;
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 IsAddop(c: char): boolean;
begin
IsAddop := c in ['+', '-'];
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;
type
symbolType = ( variableType = 1, functionType = 2 );
var
nof_symbols : integer;
symbols : array[0..26] of record
name : char;
sym_type : symbolType;
end;
procedure RememberName(name : char; sym_type : symbolType);
var
i : integer;
found : boolean;
begin
found := false;
for i := 0 to nof_symbols do begin
if symbols[i].name = name then
found := true;
end;
if i = 26 then Abort('Table of symbols overflowed');
if not found then begin
symbols[nof_symbols].name := name;
symbols[nof_symbols].sym_type := sym_type;
inc(nof_symbols);
end;
end;
procedure Ident;
var name : char;
begin
name := GetName;
if Look = '(' then begin
Match('(');
Match(')');
RememberName(name, functionType);
EmitLn('call '+name);
end else begin
RememberName(name, variableType);
EmitLn('mov eax,['+name+']');
end;
end;
procedure Factor;
begin
if Look = '(' then begin
Match('(');
Expression;
Match(')');
end else if IsAlpha(Look) then
Ident
else
EmitLn('mov eax, ' + GetNum);
end;
procedure Multiply;
begin
Match('*');
Factor;
EmitLn('pop ebx');
EmitLn('mul ebx');
end;
procedure Divide;
begin
Match('/');
Factor;
EmitLn('mov ecx,eax');
EmitLn('pop eax');
EmitLn('div ecx');
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');
EmitLn('neg eax');
end;
procedure Expression;
begin
if IsAddop(Look) then
EmitLn('MOV eax, 0')
else
Term;
while Look in ['+', '-'] do
begin
EmitLn('push eax');
case Look of
'+': Add;
'-': Subtract;
else Expected('+ or -');
end;
end;
end;
procedure Assignment;
var name : char;
begin
name := GetName;
RememberName(name, variableType);
Match('=');
Expression;
EmitLn('lea ebx,['+name+']');
EmitLn('mov [ebx],eax');
end;
procedure Init;
begin
nof_symbols := 0;
GetChar;
end;
procedure Prologue;
begin
WriteLn('[bits 32]');
WriteLn('cpu 486');
WriteLn('org 0x1000000');
{ WriteLn('section .text');
WriteLn('global main');
EmitLabel('main');
EmitLn('push ebp');
EmitLn('mov ebp, esp');
}
end;
procedure Functions;
var i : integer;
begin
for i := 0 to nof_symbols-1 do begin
if symbols[i].sym_type = FunctionType then begin
EmitLabel(symbols[i].name);
EmitLn('ret');
end;
end;
end;
procedure Variables;
var i : integer;
begin
for i := 0 to nof_symbols-1 do begin
if symbols[i].sym_type = VariableType then begin
EmitLabel(symbols[i].name);
EmitLn('dw 0');
end;
end;
end;
procedure Epilogue;
begin
EmitLn('hlt');
Functions;
Variables;
{
EmitLn('leave');
EmitLn('ret');
}
end;
begin
Prologue;
Init;
Assignment;
Match(LF);
Assignment;
if Look <> LF then Expected('Newline');
Epilogue;
end.
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