leftShift

        pub fn leftShift(self: *Self, shift: usize) void {
            if (self.num_digits == 0) {
                return;
            }
            const num_new_digits = self.numberOfDigitsLeftShift(shift);
            var read_index = self.num_digits;
            var write_index = self.num_digits + num_new_digits;
            var n: MantissaT = 0;
            while (read_index != 0) {
                read_index -= 1;
                write_index -= 1;
                n += math.shl(MantissaT, self.digits[read_index], shift);

                const quotient = n / 10;
                const remainder = n - (10 * quotient);
                if (write_index < max_digits) {
                    self.digits[write_index] = @as(u8, @intCast(remainder));
                } else if (remainder > 0) {
                    self.truncated = true;
                }
                n = quotient;
            }
            while (n > 0) {
                write_index -= 1;

                const quotient = n / 10;
                const remainder = n - (10 * quotient);
                if (write_index < max_digits) {
                    self.digits[write_index] = @as(u8, @intCast(remainder));
                } else if (remainder > 0) {
                    self.truncated = true;
                }
                n = quotient;
            }

            self.num_digits += num_new_digits;
            if (self.num_digits > max_digits) {
                self.num_digits = max_digits;
            }
            self.decimal_point += @as(i32, @intCast(num_new_digits));
            self.trim();
        }