Javascript unsigned short到signed short [英] Javascript unsigned short to signed short

问题描述

我有以下代码:

var v = [0xFF, 0xFF];
alert((v[0]<<8) | v[1]);

它会发出65535(最大卖空价值)的警报.

And it alerts 65535 (the max short value).

如何将这个字节数组视为有符号的short，并获取该数组的有符号值.

How can I treat this byte array as a signed short, and get the signed value of this array.

推荐答案

假定较高的位是符号:

var sign = v[0] & (1 << 7);
var i = ((v[0] & 0x7F) << 8) | v[1];
if (sign) {
    i = -i;
}

http://jsfiddle.net/p4TQw/1/

如果您使用 Two's补语表示形式:

var i = (((v[0] << 8) | v[1]) << 16) >> 16);

左移16位将所有位向左移动；算术右移16位将在移位时照顾符号.(JavaScript使用32位整数进行移位操作.)

The 16 bits left shift moves all bits to the left; and the arithmetic 16 bits right shift takes care of the sign while shifting. (Javascript uses 32 bits integers for shift operations.)

http://jsfiddle.net/p4TQw/3/

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