Sure it works.

But PBP uses integer math. So there are no decimals.

With STEP -2 the loop will execute 3 times, with the values 5, 3, 1 in DigLoop.
Since it's Integer math, (6-DigLoop)/2 will return 0, 1 and 2 respectively.

Code:
loop    Buf((6-DigLoop)/2) = ((Value DIG DigLoop) << 4) + Value DIG (DigLoop -1)
5       BUF(      0      ) = (       $00              ) +        0  = $00
3       BUF(      1      ) = (       $10              ) +        3  = $13
1       BUF(      2      ) = (       $80              ) +        9  = $89
hth,