int (@NotNull String str, int pos) { char ch = str.charAt(pos); if (ch >= '0' && ch <= '9') return ch - '0'; if (ch >= 'A' && ch <= 'F') return ch - 'A' + 10; if (ch >= 'a' && ch <= 'f') return ch - 'a' + 10; throw new IllegalArgumentException("unsupported char at " + pos + ":" + str); }