PRB: MOD Function w/ Negative Number May Give Different Answer

ID: Q130128

3.00 WINDOWS

  kbprb

The information in this article applies to:

Microsoft Visual FoxPro for Windows, version 3.0

SYMPTOMS

If negative numbers are used with the MOD function, it is possible that the answer returned will be different from the answer given by other applications that also incorporate a MOD function.

CAUSE

The correct definition of MOD is as follows:

   x MOD y = z where z + y * int(x/y) = x
   z = x - y * int(x/y)

Therefore:

   x MOD y = x - y * int(x/y)

In the Microsoft MOD function, we do the same as above except we use the FLOOR() function instead of INT() in order to be backward compatible with other products that use the FLOOR() function.

RESOLUTION

Below are two functions. The first function (FLOORMOD) implements the MOD with a FLOOR() function, and the second function (INTMOD) implements the MOD with an INT() function. Sometimes you may want to use the INTMOD function.

   **** MOD with FLOOR() ****
   FUNCTION FLOORMOD
      PARAMETER x,y
      z = x - FLOOR(x/y)*y
   RETURN z
   **************************

   **** MOD with INT() ******
   FUNCTION INTMOD
      PARAMETER x,y
      z = x - INT(x/y)*y
   RETURN z
   **************************

STATUS

This behavior is by design.

Additional reference words: 3.00 VFoxWin

KBCategory:   kbprb

KBSubcategory: FxprgGeneral

Keywords          : kbcode FxprgGeneral 
Version           : 3.00
Platform          : WINDOWS