Re: Bitwise operations

If I have four corners with the values 1,0,0,0 how would I go about building the index - for these values the result should be 7.

Erm. Binary 1000 is 8 not 7. Unless you invert the bits, but I don't see any call for that in a quick scan of the page you linked.

If you have an 4 element array containing the 1s & 0s, you could build the numeric value this way:

@b = qw[ 1 0 0 0 ];;

$n = 0; 
$n <<= 1, $n |= $_  for @b; 

print $n;;
8


@b = qw[ 0 1 1 1 ];;

$n = 0; 
$n <<= 1, $n |= $_  for @b; 

print $n;;
7
[download]

With the rise and rise of 'Social' network sites: 'Computers are making people easier to use everyday'

Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.

"Science is about questioning the status quo. Questioning authority".

In the absence of evidence, opinion is indistinguishable from prejudice.

Comment on Re: Bitwise operations Download Code

Replies are listed 'Best First'.
Re^2: Bitwise operations by bangor (Monk) on Jan 08, 2014 at 22:23 UTC
Hi BrowserUK, thanks for your reply. The Wikipedia page is confusing me more now - if you have a chance to look at it again you will see in the second grid diagram with the green lines each cell has a number which I believe corresponds to the binary index of the 4 corners. The top row has cells with the corners 0 0 1 0 0 0 1 1 0 0 1 1 0 0 0 1 and the values in the diagram are 13,12,12,14 But when I apply the bitwise operations I get 2,3,3,1 If I flip the values of the corners before applying the operation I get the correct results, so maybe the algorithm is missing a step or, more likely, I am completely misreading it.	[reply]
Re^3: Bitwise operations by BrowserUk (Patriarch) on Jan 09, 2014 at 05:21 UTC
If I flip the values of the corners before applying the operation I get the correct results, so maybe the algorithm is missing a step or, more likely, I am completely misreading it. I see the problem. I didn't write the article :) (It is unfortunately quite typical.) (Perhaps the explanation is the annotation that reads: "Give every cell a number based on which corners are true/false.") You can 'flip' the values after you've constructed them using: `@b = qw[ 1 0 0 0 ];; $n = 0; $n <<= 1, $n \|= $_ for @b; $n = ~$n & 0xf; ## Additional step to bitwise-not +and mask (flip) values. print $n;; 7` [download] With the rise and rise of 'Social' network sites: 'Computers are making people easier to use everyday' Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error. "Science is about questioning the status quo. Questioning authority". In the absence of evidence, opinion is indistinguishable from prejudice.	[reply] [d/l]