Changing a bit in a string

Anonymous Monk has asked for the wisdom of the Perl Monks concerning the following question:

Hello, I have a 36 bit Address string and I need to do the following in Perl: If the 31st bit of the Address = 1, make it '0'. So if the Address = 0x000000019, make it Address_new = 0x9 Any idea what is the best way to do this in Perl? I tried changing the address from decimal to binary and concatenating with zero and then in a loop, search for the 31st bit and make it zero. Somehow it is not working properly.

Comment on Changing a bit in a string

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Re: Changing a bit in a string by moritz (Cardinal) on Apr 07, 2011 at 11:53 UTC
Somehow it is not working properly. In what way did it not work? What did you do to debug it? Show your code! And read How (Not) To Ask A Question. (hints: vec and/or the bit shift and logical bit operators described in perlop might be useful). Perl 6 - second systems done right	[reply]
Re: Changing a bit in a string by salva (Canon) on Apr 07, 2011 at 12:11 UTC
`s/([13579bdf].)$/sprintf("%02x", hex($1) - 16)/ei;` [download] Though, in practice, instead of using this obscure regexp, I would probably convert it into a bit vector and use `vec` to change the bit at position 31.	[reply] [d/l] [select]
Re: Changing a bit in a string by syphilis (Archbishop) on Apr 07, 2011 at 14:09 UTC
Looks to me that the following does the job: `$address -= 16 if $address & 16;` [download] Cheers, Rob	[reply] [d/l]