rma = a * b
rma
may not alias with a
or b
. a
and b
may alias with each other.
Asserts the result fits in rma
. An upper bound on the number of limbs needed by rma is given by a.limbs.len + b.limbs.len
.
If allocator
is provided, it will be used for temporary storage to improve multiplication performance. error.OutOfMemory
is handled with a fallback algorithm.