[fpc-devel] Math.DivMod results should be signed

Michalis Kamburelis mkambi at poczta.onet.pl
Tue Mar 21 05:37:27 CET 2006


I'm concerned with using DivMod in cases when Dividend is < 0. DivMod 
declaration is

   procedure DivMod(Dividend: Integer; Divisor: Word;  var Result, 
Remainder: Word);

which means that it doesn't allow for Result and Remainder to be < 0. 
But when Dividend is < 0, Result and/or Remainder sometimes have to be < 
0. For example,

   UnsignedDivResult, UnsignedModResult: Word;
   DivResult: SmallInt absolute UnsignedDivResult;
   ModResult: SmallInt absolute UnsignedModResult;
   DivMod(-39, 20, UnsignedDivResult, UnsignedModResult);

gets me UnsignedDivResult = 65535 and UnsignedModResult = 65517. Of 
course when treating memory as signed values (DivResult and ModResult), 
I can "decipher" correct values (-1 and -19) but that's obviously 
unclean. Sure I can also just use "div" and "mod" operators, they always 
get me correct values, but I understand that doing div and mod 
separately may be slower than DivMod on some processors.

I know that DivMod arguments have to stay as Word for Delphi compat. But 
in the light of the above, it seems like a good idea to add overloaded 
DivMod version that returns Result and Remainder as signed values ?


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