this post was submitted on 31 Oct 2024
376 points (98.5% liked)

196

16423 readers
2908 users here now

Be sure to follow the rule before you head out.

Rule: You must post before you leave.

^other^ ^rules^

founded 1 year ago
MODERATORS
 
you are viewing a single comment's thread
view the rest of the comments
[–] [email protected] 42 points 4 days ago (3 children)

Just divide the number into its prime factors and then check if one of them is 2.

[–] [email protected] 19 points 4 days ago* (last edited 4 days ago) (1 children)

or divide the number by two and if the remainder is greater than

-(4^34)

but less than

70 - (((23*3*4)/2)/2)

then

true
[–] [email protected] 8 points 4 days ago (1 children)

What if the remainder is greater than the first, but not less than the latter?

Like, for example, 1?

[–] prime_number_314159 3 points 4 days ago (1 children)

Then you should return false, unless the remainder is also greater than or equal to the twenty second root of 4194304. Note, that I've only checked up to 4194304 to make sure this works, so if you need bigger numbers, you'll have to validate on your own.

[–] [email protected] 5 points 4 days ago (1 children)

i hate to bring this up, but we also need a separate function for negative numbers

[–] prime_number_314159 1 points 4 days ago

You can just bitwise AND those with ...000000001 (for however many bits are in your number). If the result is 0, then the number is even, and if it's 1, then the number is odd. This works for negative numbers because it discards the negative signing bit.

[–] tipicaldik 13 points 4 days ago (2 children)

I remember coding actionscript in Flash and using modulo (%) to determine if a number was even or odd. It returns the remainder of the number divided by 2 and if it equals anything other than 0 then the number is odd.

[–] Korne127 23 points 4 days ago

Yeah. The joke is that this is the obvious solution always used in practise, but the programmer is that bad that they don't know it and use some ridiculous alternative solutions instead.

[–] [email protected] 19 points 4 days ago

I believe that's the proper way to do it.