Been using a similar algorithm for quite some time for byte-wide key reads. I generally use 30mS debounce as some switches can be pretty noisy. You can expand this width wise and gather byte(s) from a switch matrix if required. Detect either the break edges by inverting the data read.

In P-code it looks like the following, called every 30mS:

Sample_new = Read_port
Edges = Sample_old xor Sample_new
Make_edges = Edges and Sample_new
Sample_old = Sample_new
Action_flags = Action_flags or Make_edges

in assembler:
mov a, Px
mov Sample_new, a
xrl a, Sample_old
anl a, Sample_new
mov Sample_old, Sample_new
orl Action_flags, a

You can then use jbc on Action_flags bits, assuming you have assigned it a bit-mapped register.
Make sure to initialise Sample_old at startup with:

Sample_old = Read_port

and of course

Action_flags = 0