Open source PBP bootloader

[cncmachineguy]

I have run into a snag in my brain. Here is the ASM:

rrf    ABTIME,W                            ; B0
    btfss    STATUS,C        ; Rounding                ; B0
    addlw    0xFF

Now I understand what it is doing, but I don't get why. The first line shifts ABTIME right 1 bit. This also clears bit 7. Because RRF rotates through the carry bit, ABTIME.0 gets put into the carry flag. So what is happening is this:
Shift right 1 bit
If the original (before shift) ABTIME.0=0 then add $FF to ABTIME. this seems to just clear the new ABTIME.0

So why not just do this:

tempflag = ABTIME.0
ABTIME = ABTIME >>1
IF TEMPFLAG THEN ABTIME.0 = 0

I guess my problem is did I evaluate what they are doing correctly?