It might be relevant that the CM-1's processors were tiny: they had a 1-bit word size.
Maybe this was meant to be a fast rough approximation? 1 + 1/2^-m + 1/2^-n ~= (1+1/2^-m)(1+1/2^-n). So check each bit in a fixed-point int and add a factor from a table for each 1 bit found? Then run a few rounds of Newton iteration at the end if you want it a little less rough? This goes well with the SIMD nature of the machine -- they broadcast single-bit ops one by one to all processors in parallel -- but maybe it's terrible numerically, I haven't checked.
Maybe this was meant to be a fast rough approximation? 1 + 1/2^-m + 1/2^-n ~= (1+1/2^-m)(1+1/2^-n). So check each bit in a fixed-point int and add a factor from a table for each 1 bit found? Then run a few rounds of Newton iteration at the end if you want it a little less rough? This goes well with the SIMD nature of the machine -- they broadcast single-bit ops one by one to all processors in parallel -- but maybe it's terrible numerically, I haven't checked.