Why is DivMod Limited to Words (<=65535)?
- by Andreas Rejbrand
In Delphi, the declaration of the DivMod function is
procedure DivMod(Dividend: Cardinal; Divisor: Word;
var Result, Remainder: Word);
Thus, the divisor, result, and remainder cannot be grater than 65535, a rather severe limitation. Why is this? Why couldn't the delcaration be
procedure DivMod(Dividend: Cardinal; Divisor: Cardinal;
var Result, Remainder: Cardinal);
The procedure is implemented using assembly, and is therefore probably extremely fast. Would it not be possible for the code
PUSH EBX
MOV EBX,EDX
MOV EDX,EAX
SHR EDX,16
DIV BX
MOV EBX,Remainder
MOV [ECX],AX
MOV [EBX],DX
POP EBX
to be adapted to cardinals? How much slower is the naïve attempt
procedure DivModInt(const Dividend: integer; const Divisor: integer; out result: integer; out remainder: integer);
begin
result := Dividend div Divisor;
remainder := Dividend mod Divisor;
end;
that is not (?) limited to 16-bit integers?
