fromUint

        pub fn fromUint(v_: FeUint) InvalidModulusError!Self {
            if (!v_.isOdd()) return error.EvenModulus;

            var v = v_.normalize();
            const hi = v.limbsConst()[v.limbs_len - 1];
            const lo = v.limbsConst()[0];

            if (v.limbs_len < 2 and lo < 3) {
                return error.ModulusTooSmall;
            }

            const leading = @clz(hi) - carry_bits;

            var y = lo;

            inline for (0..comptime math.log2_int(usize, t_bits)) |_| {
                y = y *% (2 -% lo *% y);
            }
            const m0inv = (@as(Limb, 1) << t_bits) - (@as(TLimb, @truncate(y)));

            const zero = Fe{ .v = FeUint.zero };

            var m = Self{
                .zero = zero,
                .v = v,
                .leading = leading,
                .m0inv = m0inv,
                .rr = undefined, // will be computed right after
            };
            m.shrink(&m.zero) catch unreachable;
            computeRR(&m);

            return m;
        }