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Reference – What does this symbol mean in PHP?

What does the << mean in this line of PHP?

$count = (1 << $count_log2) - 1;

Answer 1

this is the shift left operator.

so in your example you are shifting left the value 1 , $count_log2 times to the left.
so the value is 2^count_log2.

1 in 8 bit binary is 00000001
so if $count_log2 = 4, we need to get 2^4 = 16.

shifting left means moving the 1 left 4 times (since $count_log2 = 4).
lets do the steps.

1. 00000010 (2 in decimal)
2. 00000100 (4 in decimal)
3. 00001000 (8 in decimal)
4. 00010000 (16 in decimal)

so we got 2^4.

a common reason for using shift operation is that it takes less time for the processor to do a shift operation than using multiplication.