Bitwise Left Shift operator

Question

$a = 23;
$res = $a << 4 
print($res);

For the code snippet pasted above, the output is 368. How is it being calculated?

I expected 92.

a is 23

a in base 2 is 10111

so a in 8 bits is 00010111

Left shift 4 is 01110000

It is - 92

Can some body explain me ?

Practically, each shift to the left is equal to a multiplication with two. Since you're shifting four bits that 4 such multiplications or 4^2 which is 16. 23 * 16 is equal to 368. — Some programmer dude, Nov 17 '18 at 15:17
Perhaps you should read into it first: https://stackoverflow.com/questions/141525/what-are-bitwise-shift-bit-shift-operators-and-how-do-they-work — Daniel, Nov 17 '18 at 15:20

A l w a y s S u n n y · Accepted Answer · 2018-11-17T15:36:00.350

2

This is why it is returning 368 because $a << $b Shift the bits of $a $b steps to the left

23

256 128 64 32 16 8 4 2 1
 X   X   X  X  1 0 1 1 1

after $a << 4

368

256 128 64 32 16 8 4 2 1
 1   0   1  1  1 0 0 0 0

edited Nov 17 '18 at 15:36

answered Nov 17 '18 at 15:25

A l w a y s S u n n y

36,497
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why did you go for 9 bytes ? why we can try with 8 bytes ? I did the same, but I stopped in 8 bytes. So it was . 128 64 32 16 8 4 2 1 X X X 1 0 1 1 1 – Iynga Iyngaran Iyathurai Nov 17 '18 at 15:28
@IyathuraiIyngaran Your 9th bit is 1, you can not neglect it. – akshaypjoshi Nov 17 '18 at 15:31
1

@akshaypjoshi, got it, thanks – Iynga Iyngaran Iyathurai Nov 17 '18 at 15:33

score 1 · Answer 2 · answered Nov 17 '18 at 15:20

1

Check bitwise operator manual here

Convert 23 in binary and it is 10111 and when you perform shift left bitwise operator, its value will be 101110000 and when you convert it to decimal it becomes 368.

answered Nov 17 '18 at 15:20

akshaypjoshi

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Bitwise Left Shift operator

2 Answers2