toString

    pub fn toString(self: Const, string: []u8, base: u8, case: std.fmt.Case, limbs_buffer: []Limb) usize {
        assert(base >= 2);
        assert(base <= 36);

        if (self.eqlZero()) {
            string[0] = '0';
            return 1;
        }

        var digits_len: usize = 0;

        // Power of two: can do a single pass and use masks to extract digits.
        if (math.isPowerOfTwo(base)) {
            const base_shift = math.log2_int(Limb, base);

            outer: for (self.limbs[0..self.limbs.len]) |limb| {
                var shift: usize = 0;
                while (shift < limb_bits) : (shift += base_shift) {
                    const r = @as(u8, @intCast((limb >> @as(Log2Limb, @intCast(shift))) & @as(Limb, base - 1)));
                    const ch = std.fmt.digitToChar(r, case);
                    string[digits_len] = ch;
                    digits_len += 1;
                    // If we hit the end, it must be all zeroes from here.
                    if (digits_len == string.len) break :outer;
                }
            }

            // Always will have a non-zero digit somewhere.
            while (string[digits_len - 1] == '0') {
                digits_len -= 1;
            }
        } else {
            // Non power-of-two: batch divisions per word size.
            // We use a HalfLimb here so the division uses the faster lldiv0p5 over lldiv1 codepath.
            const digits_per_limb = math.log(HalfLimb, base, maxInt(HalfLimb));
            var limb_base: Limb = 1;
            var j: usize = 0;
            while (j < digits_per_limb) : (j += 1) {
                limb_base *= base;
            }
            const b: Const = .{ .limbs = &[_]Limb{limb_base}, .positive = true };

            var q: Mutable = .{
                .limbs = limbs_buffer[0 .. self.limbs.len + 2],
                .positive = true, // Make absolute by ignoring self.positive.
                .len = self.limbs.len,
            };
            @memcpy(q.limbs[0..self.limbs.len], self.limbs);

            var r: Mutable = .{
                .limbs = limbs_buffer[q.limbs.len..][0..self.limbs.len],
                .positive = true,
                .len = 1,
            };
            r.limbs[0] = 0;

            const rest_of_the_limbs_buf = limbs_buffer[q.limbs.len + r.limbs.len ..];

            while (q.len >= 2) {
                // Passing an allocator here would not be helpful since this division is destroying
                // information, not creating it. [TODO citation needed]
                q.divTrunc(&r, q.toConst(), b, rest_of_the_limbs_buf);

                var r_word = r.limbs[0];
                var i: usize = 0;
                while (i < digits_per_limb) : (i += 1) {
                    const ch = std.fmt.digitToChar(@as(u8, @intCast(r_word % base)), case);
                    r_word /= base;
                    string[digits_len] = ch;
                    digits_len += 1;
                }
            }

            {
                assert(q.len == 1);

                var r_word = q.limbs[0];
                while (r_word != 0) {
                    const ch = std.fmt.digitToChar(@as(u8, @intCast(r_word % base)), case);
                    r_word /= base;
                    string[digits_len] = ch;
                    digits_len += 1;
                }
            }
        }

        if (!self.positive) {
            string[digits_len] = '-';
            digits_len += 1;
        }

        const s = string[0..digits_len];
        mem.reverse(u8, s);
        return s.len;
    }