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copied!<p>You can do:</p> <pre><code>var num = str.charCodeAt(0); var lower_nibble = (num & 0xF0) >> 4; var higher_nibble = num & 0x0F; </code></pre> <p>How does it work?</p> <p>Lets suppose the bit representation of <code>num</code> is <code>abcdwxyz</code> and we want to extract <code>abcd</code> as higher nibble and <code>wxyz</code> as lower nibble.</p> <p>To extract the lower nibble we just mask the higher nibble by bitwise anding the number with <code>0x0F</code>:</p> <pre><code>a b c d w x y z & 0 0 0 0 1 1 1 1 --------------- 0 0 0 0 w x y z = lower nibble. </code></pre> <p>To extract the higher nibble we first mask the lower nibble by bitwise anding with <code>0xF0</code> as:</p> <pre><code>a b c d w x y z & 1 1 1 1 0 0 0 0 --------------- a b c d 0 0 0 0 </code></pre> <p>and then we bitwise right- shift the result right 4 times to get rid of the trailing zeros. </p> <p>Bitwise right shifting a variable 1 time will make it loose the rightmost bit and makes the left most bit zero:</p> <pre><code>a b c d w x y z >> 1 ---------------- 0 a b c d w x y </code></pre> <p>Similarly bitwise right shifting <code>2</code> times will introduce result in :</p> <pre><code>a b c d w x y z >> 2 ---------------- 0 0 a b c d w x </code></pre> <p>and bitwise right shift <code>4</code> times gives:</p> <pre><code>a b c d w x y z >> 4 ---------------- 0 0 0 0 a b c d </code></pre> <p>as clearly seen the result is the higher nibble of the byte (<code>abcd</code>).</p>

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