Two kinds of algorithms are considered.

If *** is a binary code of length

, a "soft decision" decoding algorithm for *** changes an arbitrary point of

into a nearest codeword (nearest in Euclidean distance).

Similarly, a decoding algorithm for a lattice

in

changes an arbitrary point of

into a closest lattice point. Some general methods are given for constructing such algorithms, ami are used to obtain new and faster decoding algorithms for the Gosset lattice

, the Golay code the Leech lattice.