Delphi读溢出标志

var
  a,b,c:cardinal;
begin
  a:=$80000000;
  b:=$80000000;
  c:=a+b;
end;

在汇编中,术语溢出通常是指有符号算术,意味着总和的符号与两个操作数的符号不同;对于无符号算术,术语Carry是优选的.

您可以使用纯粹的pascal中的Overflow(Carry)检查来实现添加：

// signed add - returns True if no overflow produced
function SAdd(A,B: integer; out C: integer): Boolean;
begin
  C:= A + B;
  Result:= (A xor B < 0)   // operands have different signs
        or (C xor A >= 0); // sum has the same sign as operands
end;

// unsigned add - returns True if no carry produced
function UAdd(A,B: Cardinal; out C: Cardinal): Boolean;
begin
  C:= A + B;
  Result:= (C >= A);
end;

装配中的相同功能 – Andreas解决方案的优化变体：

// Signed Add
function SAdd(A,B: Integer; out C: Integer): Boolean;
asm
        ADD   EAX,EDX
        MOV   [ECX],EAX
        SETNO AL
end;

// Unsigned Add
function UAdd(A,B: Cardinal; out C: Cardinal): Boolean;
asm
        ADD   EAX,EAX
        SETNC AL
end;