[REBOL] Re: subtracting binaries
From: greggirwin:mindspring at: 2-Apr-2004 16:43
Hi Maarten,
I know I have other things to be doing :), but this kept coming up in my
mind...wondering if doing binary math on bitsets would work.
The following is very much a proof-of-concept, but it might be an idea
worth pursuing.
-- Gregg
----------------------------------------------------------------
get-bit: func [bitset index "0 to n-1"] [either find bitset index [1][0]]
set-bit: func [bitset index "0 to n-1"] [insert bitset index]
bit-set?: func [bitset index "0 to n-1"] [found? find bitset index]
clear-bit: func [bitset index "0 to n-1"] [remove/part bitset index]
add-bitsets: func [a b /local c i n carry] [
carry: 0
c: make bitset! length? a
for i 0 (length? a) - 1 1 [
n: add get-bit a i get-bit b i
;print [get-bit a i get-bit b i n]
switch n + carry [
0 []
1 [set-bit c i carry: 0]
2 [carry: 1]
3 [set-bit c i carry: 1]
]
;repeat i length? c [prin form get-bit c i - 1] print [tab carry]
]
i: 0
if carry <> 0 [
while [bit-set? c i][
clear-bit c i
i: i + 1
]
set-bit c i
]
c
]
subtract-bitsets: func [a b] [
if a = b [return make bitset! length? a]
add-bitsets a complement b
]
mb: func [val][make bitset! val]
add-bitsets mb #{00} mb #{00}
add-bitsets mb #{01} mb #{02}
add-bitsets mb #{F0} mb #{0F}
add-bitsets mb #{FF} mb #{FF}
add-bitsets mb #{FF} mb #{01}
subtract-bitsets mb #{00} mb #{00}
subtract-bitsets mb #{02} mb #{01}
subtract-bitsets mb #{FF} mb #{0F}
subtract-bitsets mb #{FF} mb #{FF}
subtract-bitsets mb #{00} mb #{01}
subtract-bitsets mb #{00} mb #{FF}
