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Editorial Team
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Asked: 2026-06-13T11:48:53+00:00

I’ve been trying to learn more about PHP’s bitwise operators today, and I’m having

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I’ve been trying to learn more about PHP’s bitwise operators today, and I’m having a little trouble with the ~ operator. Following online tutorials, I’ve seen that it reverses set bits in a number. For instance, if you had a byte equal to 7:

    |------------------------------------|
    | 128 | 64 | 32 | 16 | 8 | 4 | 2 | 1 |
    |------------------------------------|
    |  0  | 0  | 0  | 0  | 0 | 1 | 1 | 1 |
    |------------------------------------|

And reversed it using ~7:

    |------------------------------------|
    | 128 | 64 | 32 | 16 | 8 | 4 | 2 | 1 |
    |------------------------------------|
    |  1  | 1  | 1  | 1  | 1 | 0 | 0 | 0 |
    |------------------------------------|

Wouldn’t that be equal to 248 and not -8?

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1 Answer

  1. Editorial Team

    No. The reason for this is the Two’s complement.

    The very first bit of each number has got a negative value (-232 in PHP, as PHP uses 32bit (= 4 byte) numbers). When the bit is set to 1 the whole number will become negative. Therefore when using the not-operator (~) this bit will change and the number will become negative.

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