学步园

今天搜到的一个知识，分享
一下。

1．故事的起源

      “endian”这个词出自《格列佛游记》
。小人国的内战就源于吃鸡蛋时是究竟从大头(Big-Endian)敲开还是从小头(Little-Endian)敲开，由此曾发生过六次叛乱，其中一个皇帝送了命，另一个丢了王位。
      我们一般将endian翻译成“字节序”，将big endian和little endian称作“大尾”和“小尾”(我宁可称为“大字节序”与“小字节序”，不受“尾”字的干扰)。

2.正文
     谈到字节序的问题，必然牵涉到两大CPU派系。那就是Motorola的PowerPC系列CPU和 Intel的x86系列CPU。PowerPC系列采用big endian方式存储数据
，而x86系列则采用little endian方式存储数据。那么究竟什么是big endian，什么又是little endian呢？

3.下面附一转载的代码
，可实现两种字序下byte[]数组与int之间的互相转换：

//工具类<br /> package lab.sodino.endian;<br /> /**<br /> * @author Sodino E-mail:sodinoopen@hotmail.com<br /> * @version Time 2011-1-14 下午03:19:12<br /> */<br /> public class EndianUtil {<br /> /**<br /> * 将字节数组转为 Java 中的 int 数值<br /> *<br /> * @param bys<br /> * 字节数组<br /> * @param start<br /> * 需要转换的起始索引点<br /> * @param len<br /> * 需要转换的字节长度<br /> * @param isBigEndian<br /> * 是否是 BE（true -- BE 序，false -- LE 序） * @return<br /> */<br /> public static Object Bytes2NumWrapper(byte[] data, int start, int len,<br /> Class wrapper, boolean isBigEndian) {<br /> Object obj = null;<br /> int wrapperSize = 0;<br /> int move = 0;<br /> if (wrapper == Byte.class) {<br /> byte tmp = 0;<br /> wrapperSize = Byte.SIZE;<br /> move = Byte.SIZE / Byte.SIZE;<br /> for (int i = start, k = start + len % (wrapperSize / Byte.SIZE + 1); i < k; i++) {<br /> // ((i - start) % move))亦可只写为(i - start)<br /> tmp |= (data[i] & 0xff) << ((isBigEndian ? (k - i - 1)<br /> : ((i - start) % move)) * Byte.SIZE);<br /> }<br /> obj = new Byte(tmp);<br /> } else if (wrapper == Short.class) {<br /> short tmp = 0;<br /> wrapperSize = Short.SIZE;<br /> move = Short.SIZE / Byte.SIZE;<br /> for (int i = start, k = start + len % (wrapperSize / Byte.SIZE + 1); i < k; i++) {<br /> // ((i - start) % move))亦可只写为(i - start)<br /> tmp |= (data[i] & 0xff) << ((isBigEndian ? (k - i - 1)<br /> : ((i - start) % move)) * Byte.SIZE);<br /> }<br /> obj = new Short(tmp);<br /> } else if (wrapper == Integer.class) {<br /> int tmp = 0;<br /> wrapperSize = Integer.SIZE;<br /> move = Integer.SIZE / Byte.SIZE;<br /> for (int i = start, k = start + len % (wrapperSize / Byte.SIZE + 1); i < k; i++) {<br /> // ((i - start) % move))亦可只写为(i - start)<br /> tmp |= (data[i] & 0xff) << ((isBigEndian ? (k - i - 1)<br /> : ((i - start) % move)) * Byte.SIZE);<br /> }<br /> System.out.println("tmp=" + Integer.toHexString(tmp)<br /> + "/n----test End");<br /> obj = new Integer(tmp);<br /> } else if (wrapper == Long.class) {<br /> long tmp = 0;<br /> wrapperSize = Long.SIZE;<br /> move = Long.SIZE / Byte.SIZE;<br /> for (int i = start, k = start + len % (wrapperSize / Byte.SIZE + 1); i < k; i++) {<br /> // 注意此处需得标明 0xff为l(long)型<br /> // ((i - start) % move))亦可只写为(i - start)<br /> tmp |= (data[i] & 0xffl) << ((isBigEndian ? (k - i - 1)<br /> : ((i - start) % move)) * Byte.SIZE);<br /> }<br /> obj = new Long(tmp);<br /> }<br /> return obj;<br /> }<br /> /**<br /> * @param num<br /> * 指定的整型数<br /> * @param isBigEndian<br /> * 是否是大字节序。<br /> */<br /> public static byte[] NumWrapper2Bytes(Object num, boolean isBigEndian) {<br /> byte[] data = null;<br /> int wrapperSize = 0;<br /> if (num instanceof Byte) {<br /> data = new byte[1];<br /> data[0] = ((Byte) num).byteValue();<br /> } else if (num instanceof Short) {<br /> wrapperSize = Short.SIZE;<br /> short tmp = ((Short) num).shortValue();<br /> data = new byte[wrapperSize / Byte.SIZE];<br /> for (int i = 0; i < data.length; i++) {<br /> data[i] = (byte) (tmp >>> ((isBigEndian ? (data.length - i - 1)<br /> : i))<br /> * Byte.SIZE);<br /> }<br /> } else if (num instanceof Integer) {<br /> wrapperSize = Integer.SIZE;<br /> int tmp = ((Integer) num).intValue();<br /> data = new byte[wrapperSize / Byte.SIZE];<br /> for (int i = 0; i < data.length; i++) {<br /> data[i] = (byte) (tmp >>> ((isBigEndian ? (data.length - i - 1)<br /> : i))<br /> * Byte.SIZE);<br /> }<br /> } else if (num instanceof Long) {<br /> wrapperSize = Long.SIZE;<br /> long tmp = ((Long) num).longValue();<br /> data = new byte[wrapperSize / Byte.SIZE];<br /> for (int i = 0; i < data.length; i++) {<br /> data[i] = (byte) (tmp >>> ((isBigEndian ? (data.length - i - 1)<br /> : i))<br /> * Byte.SIZE);<br /> }<br /> }<br /> return data;<br /> }<br /> }<br /> //测试类<br /> package lab.sodino.endian;<br /> import java.io.ByteArrayOutputStream;<br /> import java.io.File;<br /> import java.io.FileInputStream;<br /> import java.io.FileOutputStream;<br /> /**<br /> * @author Sodino E-mail:sodinoopen@hotmail.com<br /> * @version Time�?011-1-14 下午05:30:46<br /> */<br /> public class EndianMain {<br /> public static void main(String[] args) {<br /> testByte();<br /> testShort();<br /> testInteger();<br /> testLong();<br /> }<br /> public static void testByte() {<br /> byte[] data = EndianUtil.NumWrapper2Bytes(new Byte((byte) 0x01), false);<br /> System.out.print("data.length=" + data.length + " Content:");<br /> for (int i = 0; i < data.length; i++) {<br /> System.out.print(data[i] + " ");<br /> }<br /> System.out.println("/nEnd NumWrapper2Bytes");<br /> Object obj = EndianUtil.Bytes2NumWrapper(data, 0, data.length,<br /> Byte.class, false);<br /> byte num = ((Byte) obj).byteValue();<br /> System.out.println(Integer.toHexString(num));<br /> System.out.println("End Bytes2NumWrapper");<br /> }<br /> public static void testShort() {<br /> byte[] data = EndianUtil.NumWrapper2Bytes(new Short((short) 0x0102),<br /> false);<br /> System.out.print("data.length=" + data.length + " Content:");<br /> for (int i = 0; i < data.length; i++) {<br /> System.out.print(data[i] + " ");<br /> }<br /> System.out.println("/nEnd NumWrapper2Bytes");<br /> Object obj = EndianUtil.Bytes2NumWrapper(data, 0, data.length,<br /> Short.class, false);<br /> short num = ((Short) obj).shortValue();<br /> System.out.println("Hex:0x" + Integer.toHexString(num));<br /> System.out.println("End Bytes2NumWrapper");<br /> }<br /> public static void testInteger() {<br /> byte[] data = EndianUtil.NumWrapper2Bytes(new Integer(0x01020304),<br /> false);<br /> System.out.print("data.length=" + data.length + " Content:");<br /> for (int i = 0; i < data.length; i++) {<br /> System.out.print(data[i] + " ");<br /> }<br /> System.out.println("/nEnd NumWrapper2Bytes");<br /> Object obj = EndianUtil.Bytes2NumWrapper(data, 0, data.length,<br /> Integer.class, false);<br /> int num = ((Integer) obj).intValue();<br /> System.out.println("Hex:0x" + Integer.toHexString(num));<br /> System.out.println("End Bytes2NumWrapper");<br /> }<br /> public static void testLong() {<br /> byte[] data = EndianUtil.NumWrapper2Bytes(<br /> new Long(0x0102030405060708l), false);<br /> System.out.print("data.length=" + data.length + " Content:");<br /> for (int i = 0; i < data.length; i++) {<br /> System.out.print(data[i] + " ");<br /> }<br /> System.out.println("/nEnd NumWrapper2Bytes");<br /> Object obj = EndianUtil.Bytes2NumWrapper(data, 0, data.length,<br /> Long.class, false);<br /> long num = ((Long) obj).longValue();<br /> System.out.println("Hex:0x" + Long.toHexString(num));<br /> System.out.println("End Bytes2NumWrapper");<br /> }<br /> }<br />

本文内容归CSDN博客博主Sodino
所有
转载请注明出处:
http://blog.csdn.net/sodino/archive/2010/12/21/6088073.aspx