fn add(r: *Mutable, a: Const, b: Const) void
r = a + b r, a and b may be aliases.
Asserts the result fits in r. An upper bound on the number of limbs needed by r is @max(a.limbs.len, b.limbs.len) + 1.
r
@max(a.limbs.len, b.limbs.len) + 1
r: *Mutable,
a: Const,
b: Const,