1. 文件读取
read-byte：
(with-open-file (instream filename
:direction :input
:element-type 'unsigned-byte
:if-exists :supersede)
(do ((line (read-byte instream nil 'eof) (read-byte instream nil 'eof)))
((eq line 'eof) "end of file.")
(do-something)))
read word：
(defun read-word (s)
"Reads 16-bit word from the stream"
(let* ((msb (ash (read-byte s) 8))
(lsb (read-byte s))
(word (logior msb lsb)))
word))
2. 二进制运算
ash：
(ash bin-data num) ;;表示 bin-data*(2^num)，num>0为左移位操作；num<0为右移操作
(ash 16 1) > 32
(ash 16 -1) > 8logior：
(logior 1 2 4 8) => 15 ;;逻辑或运算logand：
(logand 1 2 4 8) => 0 ;;逻辑与运算logxor：
(logxor 3 5) => 6 ;;逻辑异或运算byte:
(byte a b) ;;返回一个cons对象(a . b)，意义为从第b个bit开始，取a个bit，设数据共n个字节b为0~2^n - 1。
(byte 8 0) => (8 . 0)ldb:
(ldb (byte 8 0) #xabcd) => 171 ;;即0xab，从bit0开始取8个bit
(ldb (byte 8 8) #xabcd) => 205 ;;即0xcd，从bit8开始取8个bit
