I need to convert an array of integers to a little endian bitmask using Ruby. Any links or hints would be appreciated.
the example says [2,7,9,11] => "4205"
a = [2,7,9,11] # 4205
b = [1,2,3,4] # 0F00
def array_to_mask(arr)
mask = 0
arr.each do |i|
mask = mask | (1 << i)
end
return mask.to_s(16)
end
p array_to_mask(a) # a84
p array_to_mask(b) # 1e
This does not work, but am i on the right track?
Can't you use arr.pack()? It has options for byte order.
Update: Ok I've taken a look at the documentation you mentioned and the only way I can make the example work is this:
7 2 11 9 (decimal index count)
0 1 0 0 0 0 1 0 0 0 0 0 0 1 0 1 (bits)
4 2 0 5 (nibbles, in hex)
But that would mean that would mean that the 4205 are 4 nibbles that together represent 2 bytes? That is the only way I could make the first byte have the second and seventh bit set (reading little endian).
... This is more of an 'understanding the docs' issue than it it a ruby issue.
So the array solution is not the one you need, because you need to set the individual bits in a number. This is best achieved using (left) bit shift << and or'ing | the results together.
Enfora sent me a calculator which I examined to write a function. Hopefully this explanation will help whoever is next to try this.
values: [2,7,9,11]
Bits: | 8 7 6 5 | 4 3 2 1 | 16 15 14 13 | 12 11 10 9 |
Binary: | 0 1 0 0 | 0 0 1 0 | 0 0 0 0 | 0 1 0 1 |
Hex: | 4 | 2 | 0 | 5 |