node.js - Slice a byte into bits

buffer, javascript, node.js

Solution

Use a bitmask, an octet is 8 bits so you can do something like the following:

for (var i = 7; i >= 0; i--) {
   var bit = octet & (1 << i) ? 1 : 0;
   // do something with the bit (push to an array if you want a sequence)
}

Example: http://jsfiddle.net/3NUVq/

You could probably make this more efficient, but the approach is pretty straightforward. This loops over an offset `i`, from 7 down to 0, and finds the `i`th bit using the bitmask `1 << i`. If the `i`th bit is set then `bit` becomes `1`, otherwise it will be `0`.

Problem

How can I take an octet from the buffer and turn it into a binary sequence? I want to decode protocol rfc1035 through node.js but find it difficult to work with bits. Here is a code, but it does not suit me - because it is a blackbox for me: ``` var sliceBits = function(b, off, len) { var s = 7 - (off + len - 1); b = b >>> s; return b & ~(0xff << len); }; ```

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