Negative dividend: makes DivMod raise EDivByZero, makes mod return wrong value

Original Reporter info from Mantis: Michalis @michaliskambi

• Reporter name: Michalis Kamburelis

Description:

(Observed with released 2.4.0, tagging with "2.4.1" in mantis as there's no "2.4.0" choice yet.)

Submitting this as one bug, although I'm not sure --- maybe these are two not related bugs (one for Math.DivMod, one for the "mod" operator). Neither of these problems were observed with 2.2.4.

The program calculates "-9 div/mod 5" in two ways: 1. call "div" and "mod" operators separately, 2. call DivMod.

Running with 2.2.4 we get correct results from both approaches:

$ fpc -gl divmod.pas
$ ./divmod
-1 -4
-1 -4

Running with 2.4.0 we get:

$ fpc -gl divmod.pas
$ ./divmod
-1 2
An unhandled exception occurred at $080637FD :

EDivByZero : Division by zero<br/>
  $080637FD
  $0804812E  main,  line 10 of divmod.pas

So the "-9 mod 5" returns wrong value (2) and DivMod(-9, ...) raises EDivByZero exception.

Mantis conversion info:

• Mantis ID: 15453
• OS: Debian GNU/Linux
• OS Build: (testing)
• Platform: i386
• Version: 2.4.0
• Fixed in version: 2.4.2
• Fixed in revision: 15201 (#78e19bdd)
• Target version: 2.4.2