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--- chess:programming:bit_operations [2021/11/03 11:45] – peter
+++ chess:programming:bit_operations [2021/11/05 09:55] (current) – peter
@@ Line 3: / Line 3: @@
 ^Expression^Description^Example^
 |x & y|AND the bits of x with those of y|21 & 7 = 10101 & 00111 = 00101 = 5|
-|x <nowiki>|</nowiki> y|OR the bits of x with those of y|21 | 7 = 10101 | 00111 = 10111 = 23|
+|x <nowiki>|</nowiki> y|OR the bits of x with those of y|21 <nowiki>|</nowiki> 7 = 10101 <nowiki>|</nowiki> 00111 = 10111 = 23|
-|x <nowiki>^</nowiki> y|XOR the bits of x with those of y|21 ^ 7 = 10101 ^ 00111 = 10010 = 18|
+|x <nowiki>^</nowiki> y|XOR the bits of x with those of y|21 <nowiki>^</nowiki> 7 = 10101 <nowiki>^</nowiki> 00111 = 10010 = 18|
 |~x|Inverting (complementing) the bits of x (0 -> 1 and 1 -> 0)|~7 = 11111111111111000 = 65528|
 |x << y|Shift the bits of x to the left y positions|25 << 3 = 10101 << 3 = 10101000 = 168|
 |x >> y|Shift the bits of x to the right y positions|25 >> 3 = 10101 >> 3 = 00010 = 2|
+----
+===== Get only even or odd bits =====
+Take a number, say 12345678.
+  * In Binary, this is 00000000101111000110000101001110.
+Apply an even mask against it:
+<code>
+00000000101111000110000101001110   &    (n)
+10101010101010101010101010101010        (0xAAAAAAAA)
+————————————————————————————————
+00000000101010000010000000001010        (Contains all even bits)
+</code>
+Apply an odd mask against it:
+<code>
+00101101011001010111000110001001   &    (n)
+01010101010101010101010101010101        (0x55555555)
+————————————————————————————————
+00000000000101000100000101000100        (Contains all odd bits)
+</code>
+<WRAP info>
+**NOTE:**  Use Masks.
+  * Mask **0xAAAAAAAA** has all its even bits set.
+    * Its bitwise AND with a number will separate out the even bits.
+    * 1010 1010 1010 1010 1010 1010 1010 1010
+  * Mask **0x55555555** has all its odd bits set.
+    * Its bitwise AND with a number will separate out the odd bits.
+    * 1010 1010 1010 1010 1010 1010 1010 1010
+</WRAP>
+----