Encode/Decode cell addresses into integers using ruby

bitshift.rb

#!/usr/local/bin/ruby -w

# Bit masks
MASKA = 0XFFFF
MASKB = 0XFFFFFFFF
MASKR = 0XFFFFFFFFFFFFFFFF

def letter? ch; ch =~ /[a-zA-Z]/ end
def number? ch; ch =~ /[0-9]/    end

# Returns the two letters that conforms 
# the column name, or one letter and a 
# null char if the lenght of the column
# name is 1.
# So, the result is always twoc chars [a,b].
def split col
	a = col[0].ord
	b = '_'.ord
	b = col[1].ord if col.length == 2
	[a, b]
end

# Parses a cell address and returns:
# [true, col, row] is the address is valid, or
# [false, nil, nil] if the parse failed.
def parse addr
	colsize  = 0
	colsize += 1 if letter? addr[0]
	colsize += 1 if letter? addr[1]

	return [false, nil, nil] if colsize == 0

	col = addr[0..colsize-1]
	row = addr[colsize..-1].to_i
	[true, col, row]
end

# Returns an encoded value that represents a 
# cell address or -1 if arguments are invalid.
# Valid column values are [a..zz] and valid 
# row values are [1..65535].
def encode addr
	ok, col, row = parse(addr)
	return -1 unless ok

	a, b = split(col)
	encoded = 0
	encoded |= (a   <<  8)
	encoded |= (b   << 16)
	encoded |= (row << 32)

	encoded
end

# Decodes and encoded cell address. 
# (See encode method.)
def decode encoded
	a = (encoded & MASKA) >>  8
	b = (encoded & MASKB) >> 16
	r = (encoded & MASKR) >> 32

	return "#{a.chr}#{r}" if b.chr == '_'
	return "#{a.chr}#{b.chr}#{r}"
end

def main
	addr1, addr2 = "A1", "AZ65535"
	a1      = encode addr1
	az65535 = encode addr2

	puts "#{addr1} encoded: #{a1}"
	puts "#{addr2} encoded: #{az65535}"
	puts ""
	puts "#{a1} decoded: #{decode(a1)}"
	puts "#{az65535} decoded: #{decode(az65535)}"
end

main