package java.io;
/**
* Utility methods for packing/unpacking primitive values in/out of byte arrays
* using big-endian byte ordering.
*/
class Bits {
/*
* Methods for unpacking primitive values from byte arrays starting at
* given offsets.
*/
static boolean getBoolean(byte[] b, int off) {
return b[off] != 0;
}
static char getChar(byte[] b, int off) {
return (char) ((b[off + 1] & 0xFF) +
(b[off] << 8));/*从offer 开始,取出一个char,byte是8位，若对char,byte,short进行移位，自动转换为int，b[off]长度为32位，移位不会溢出。大端：高位数在低地址*/
}
static short getShort(byte[] b, int off) {
return (short) ((b[off + 1] & 0xFF) +
(b[off] << 8));
}
static int getInt(byte[] b, int off) { //需要截取4个byte，按大端法构成一个int
return ((b[off + 3] & 0xFF) ) +
((b[off + 2] & 0xFF) << 8) +
((b[off + 1] & 0xFF) << 16) +
((b[off ] ) << 24);
}
static float getFloat(byte[] b, int off) {
return Float.intBitsToFloat(getInt(b, off));
}
static long getLong(byte[] b, int off) {
return ((b[off + 7] & 0xFFL) ) +
((b[off + 6] & 0xFFL) << 8) +
((b[off + 5] & 0xFFL) << 16) +
((b[off + 4] & 0xFFL) << 24) +
((b[off + 3] & 0xFFL) << 32) +
((b[off + 2] & 0xFFL) << 40) +
((b[off + 1] & 0xFFL) << 48) +
(((long) b[off]) << 56);
}
static double getDouble(byte[] b, int off) {
return Double.longBitsToDouble(getLong(b, off));
}
/*
* Methods for packing primitive values into byte arrays starting at given
* offsets.
*/
static void putBoolean(byte[] b, int off, boolean val) {
b[off] = (byte) (val ? 1 : 0);
}
static void putChar(byte[] b, int off, char val) {
b[off + 1] = (byte) (val ); //将char转换成byte数组，按大端法：char（16位）的高8位应该在b[off]，低8位在b[off+1]中。>>>是无符号右移
b[off ] = (byte) (val >>> 8);
}
static void putShort(byte[] b, int off, short val) {
b[off + 1] = (byte) (val );
b[off ] = (byte) (val >>> 8);
}
static void putInt(byte[] b, int off, int val) {
b[off + 3] = (byte) (val );
b[off + 2] = (byte) (val >>> 8);
b[off + 1] = (byte) (val >>> 16);
b[off ] = (byte) (val >>> 24);
}
static void putFloat(byte[] b, int off, float val) {
putInt(b, off, Float.floatToIntBits(val));
}
static void putLong(byte[] b, int off, long val) {
b[off + 7] = (byte) (val );
b[off + 6] = (byte) (val >>> 8);
b[off + 5] = (byte) (val >>> 16);
b[off + 4] = (byte) (val >>> 24);
b[off + 3] = (byte) (val >>> 32);
b[off + 2] = (byte) (val >>> 40);
b[off + 1] = (byte) (val >>> 48);
b[off ] = (byte) (val >>> 56);
}
static void putDouble(byte[] b, int off, double val) {
putLong(b, off, Double.doubleToLongBits(val));
}
}