CODEWITHSUNDEEP
javascriptbit-manipulationbitwise-operators
hsz
hsz

Reputation: 152216

Bitwise test in JavaScript

I hava a following bit string:

var input = '11100001';

I want to check if eight bit is present, so I have tried with:

input & '10000000'

but it gives me 8918528. How should I test it ?

Upvotes: 1

Views: 756

Answers (2)

sampathsris
sampathsris

Reputation: 22280

Adding to @pawel's excellent answer, let me explain why you get 8918528:

As soon as JavaScript sees this:

'11100001' & '10000000'

it will try to cast the two strings to integers; Integers in base 10 precisely. So we get:

11100001 (base10) & 10000000 (base10)

which is,

101010010101111101100001 (base2) & 100110001001011010000000 (base2)

Applying bit-wise AND,

101010010101111101100001 &
100110001001011010000000
------------------------
100010000001011000000000 (base2)

Which is,

8918528 (base10)

Upvotes: 4

pawel
pawel

Reputation: 36965

You're trying to do a bitwise AND on two strings, which implicitly converts them to integers assuming base 10. You should parse them to integers explicitly supplying the base:

parseInt(input,2) & parseInt('10000000',2)
// 128

Edit: to check if n-th bit is set you could just shift to right by n-1 bits and check if it's 1

parseInt(input,2) >> 7 & 1 === 1

Upvotes: 7

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