Day 049 - Getting sign of unsigned numbers...

mallardz

17 posts

#2466

9 years, 2 months ago Edited by mallardz on February 6, 2015, 2:11pm

I don't quite understand the code at line 418 in handmade.cpp:

    uint32 StartTileX = OldPlayerP.AbsTileX;
    uint32 StartTileY = OldPlayerP.AbsTileY;
    uint32 EndTileX = NewPlayerP.AbsTileX;
    uint32 EndTileY = NewPlayerP.AbsTileY;

    if(EndTileY > StartTileY)
    {
        int x = 4;
    }
    
    int32 DeltaX = SignOf(EndTileX - StartTileX);
    int32 DeltaY = SignOf(EndTileY - StartTileY);

We seem to be testing the sign of the result of an operation between two unsigned values...
Surely this will always be positive?
Are we just missing a cast?

mrmixer

Simon Anciaux

1341 posts

#2467

Day 049 - Getting sign of unsigned numbers...

9 years, 2 months ago Edited by Simon Anciaux on February 6, 2015, 2:32pm Reason: Typos

You can subtract 2 unsigned values and get a signed value.

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uint32 a = 1;
uint32 b = 2;
int32 c = a - b; // c = -1

mallardz

17 posts

#2468

Day 049 - Getting sign of unsigned numbers...

9 years, 2 months ago

Ah ok, so as the SignOf function parameter is defined as a signed int it all works. I get it, thanks!