PHP - converting bitmask

Question

Say I assign the following fruits:

array ('1' => 'apple', '2' => 'banana', '4' => 'grape', '8' => 'orange')

If I wanted to represent apple and banana, I could just do the following: 0001 OR 0010 to get 0011 (or 3), right?

Given the number 3, how do I convert that to 1 and 2?

No, neither. He should be using the bit-wise & and | if anything. — mario
– mario, Commented Jul 1, 2011 at 1:37
FYI, it's easier to produce proper bit masks with the bitwise shift left operator: 2 << 3; // 8 — Jonah
– Jonah, Commented Jul 1, 2011 at 1:41
@Jonah In order to produce powers of 2, it is a lot easier to use bitshift instead of power. — Hyperboreus
– Hyperboreus, Commented Jul 1, 2011 at 1:42

hakre · Accepted Answer · 2012-12-18 19:09:47Z

3

All keys will be loaded into $keys:

$keys = array();
$value = 3;

foreach ($arr as $key => $val)
{
   if ($value & $key)
   {
      $keys[] = $key;
   }
}

hakre

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answered Jul 1, 2011 at 1:39

user142162

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Comments

Hyperboreus · Accepted Answer · 2011-07-01 01:38:36Z

2

Generally you use bitmasks this way (language is irrelevant)

BANANA = 0x1
APPLE = 0x2
GRAPE = 0x4
LEMON = 0x8
PAPAYA = 0x10
GUAYABA = 0x20


myFavoriteFruits = BANANA | GRAPE // I like both bananas and grapes.

Now to test if I like Bananas you evalute:

myFavoriteFruits & BANANA

answered Jul 1, 2011 at 1:38

Hyperboreus

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jcomeau_ictx · Accepted Answer · 2011-07-01 01:36:48Z

1

use the bitwise AND (&) operator in a loop to test the bits.

answered Jul 1, 2011 at 1:36

jcomeau_ictx

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looks like Tim Cooper provided one :^)