PROGRAMMING     CLIMBING

  minte9
reminder




Last update:   30-03-2022

Base

Everyday numbering system is BASE 10
 
// BASE 10

4768 = 4000 + 700 + 60 + 8

4 * 10 * 10 * 10 + // 4768
     7 * 10 * 10 + 
          6 * 10 +
               8

// BASE 2

45 = 32 + 8 + 4 + 1

0 * 2 * 2 * 2 * 2 * 2 * 2 * 2 + // 00101101
    0 * 2 * 2 * 2 * 2 * 2 * 2 + 
        1 * 2 * 2 * 2 * 2 * 2 + 
            0 * 2 * 2 * 2 * 2 + 
                1 * 2 * 2 * 2 +
                    1 * 2 * 2 +
                        0 * 2 +
                            1

Byte

A bit is a representation of 1 or 0 / A byte is made up of 8 bits.
 
// highest value of a byte is 255

1 + 2 + 4 + 8 + 16 + 32 + 64 + 128 = 255 // 11111111

AND

Bits that are set in both $a and $b are set
 
/**
 * Bitwise AND
 * 
 * Bits set in both $a and $b
 */

$a = 9;         // 8 + 1; 00001001
$b = 10;        // 8 + 2; 00001010

echo $a & $b;   // 8

$a = 36;        // 32 + 4; 00100100
$b = 103;       // 64 + 32 + 4 + 2 + 1; 01100111

echo $a & $b;   // 36

OR

Bits that are set in either $a or $b are set
 
/**
 * Bitwise OR
 * 
 * Bits set either in $a or $b
 */

$a = 9;         // 8 + 1; 00001001
$b = 10;        // 8 + 2; 00001010

echo $a | $b;   // 11

NOT BOTH

Bits that are set in $a or $b but not both are set.
 
/**
 * Bitwise NOT BOTH
 * 
 * Bits set in $a or $b but not in both
 */

$a = 9;         // 8 + 1; 00001001
$b = 10;        // 8 + 2; 00001010

echo $a ^ $b;   // 3

NOT

The NOT operator wants to know what is set in $a but NOT set in $b
 
/**
 * Bitwise NOT
 * 
 * Bits set in $a but not in $b
 */

$a = 9;         // 8 + 1; 00001001
$b = 10;        // 8 + 2; 00001010

echo $a & ~$b;  // 1

$a = 9;         // 8 + 1; 00001001
$b = 10;        // 8 + 2; 00001010

echo ~$a & $b;  // 2

Shift

Shift the bits of $a $b steps
 
/**
 * Bitwise SHIFT
 * 
 * Shift bits of $a $n steps.
 * 
 * It rovides an easy (and very fast) way of ...
 * multiplying integers by a power of two.
 */

// Left
$a = 16;        // 00010000
echo $a << 2;   // 01000000 = 64

// Right
$a = 16;        // 00010000
echo $a >> 2;   // 00000100 = 4

// Multipy
$a = 1;         // 00000001
echo $a << 2;   // 00000100 = 4

// Demultiply
$a = 8;         // 00001000
echo $a >> 2;   // 00000010 = 2

Questions     github Operators
String
        A B C D E F
🔔
1/6