Fault tolerance can be simulated in software. One example of such a technique is the sequence
ensure|x2 - y |< tolerable by x := SqrtA(y) else x := SqrtB(y) else error
Here, multiple versions of a function which computes a square root are provided, increasing the likelihood that the square root value returned satisfies some criterion.
Knowledgeable compilers which produce code for fault-tolerant systems should be aware of the redundancies in the architecture. Much research is needed to make this a reality.