powWithEncodedExponentInternal

        fn powWithEncodedExponentInternal(self: Self, x: Fe, e: []const u8, endian: Endian, comptime public: bool) NullExponentError!Fe {
            var acc: u8 = 0;
            for (e) |b| acc |= b;
            if (acc == 0) return error.NullExponent;

            const was_montgomery = x.montgomery;

            var out = self.one();
            self.toMontgomery(&out) catch unreachable;

            if (public and
                (e.len < 3 or (e.len == 3 and e[if (endian == .big) 0 else 2] <= 0b1111)))
            {
                // Do not use a precomputation table for short, public exponents
                var x_m = x;
                if (!x.montgomery) {
                    self.toMontgomery(&x_m) catch unreachable;
                }
                var s = switch (endian) {
                    .big => 0,
                    .little => e.len - 1,
                };
                while (true) {
                    const b = e[s];
                    var j: u3 = 7;
                    while (true) : (j -= 1) {
                        out = self.montgomerySq(out);
                        const k: u1 = @truncate(b >> j);
                        if (k != 0) {
                            const t = self.montgomeryMul(out, x_m);
                            @memcpy(out.v.limbs(), t.v.limbsConst());
                        }
                        if (j == 0) break;
                    }
                    switch (endian) {
                        .big => {
                            s += 1;
                            if (s == e.len) break;
                        },
                        .little => {
                            if (s == 0) break;
                            s -= 1;
                        },
                    }
                }
            } else {
                // Use a precomputation table for large exponents
                var pc: [15]Fe = [1]Fe{x} ++ @as([14]Fe, @splat(self.zero));
                if (!x.montgomery) {
                    self.toMontgomery(&pc[0]) catch unreachable;
                }
                for (1..pc.len) |i| {
                    pc[i] = self.montgomeryMul(pc[i - 1], pc[0]);
                }
                var t0 = self.zero;
                var s = switch (endian) {
                    .big => 0,
                    .little => e.len - 1,
                };
                while (true) {
                    const b = e[s];
                    for ([_]u3{ 4, 0 }) |j| {
                        for (0..4) |_| {
                            out = self.montgomerySq(out);
                        }
                        const k = (b >> j) & 0b1111;
                        if (public or std.options.side_channels_mitigations == .none) {
                            if (k == 0) continue;
                            t0 = pc[k - 1];
                        } else {
                            for (pc, 0..) |t, i| {
                                t0.v.cmov(ct.eql(k, @as(u8, @truncate(i + 1))), t.v);
                            }
                        }
                        const t1 = self.montgomeryMul(out, t0);
                        if (public) {
                            @memcpy(out.v.limbs(), t1.v.limbsConst());
                        } else {
                            out.v.cmov(!ct.eql(k, 0), t1.v);
                        }
                    }
                    switch (endian) {
                        .big => {
                            s += 1;
                            if (s == e.len) break;
                        },
                        .little => {
                            if (s == 0) break;
                            s -= 1;
                        },
                    }
                }
            }
            if (!was_montgomery) {
                self.fromMontgomery(&out) catch unreachable;
            }
            return out;
        }