# Bit flags

## Definition

Bit flags are constants which each denotes a single unique case in one situation and can be combined to form different, unique cases. They are called bit flags, because when bits are used to denote a cases, we observe they are indeed single and unique and can be combined to form different unique combinations.

Bit flags are often used as integers:

 Bit pattern - Integer value 0001 - 1 0010 - 2 0100 - 4 1000 - 8

These can be combined to form, for example:

 Bit pattern - Integer value 1001 - 9 0110 - 6 1110 - 14 0101 - 5

## Example

When we look at blit flags for example, we see the values:

 Constant - Value - Description B_HMIRROR - 1 - Blit the graph horizontally mirrored. B_VMIRROR - 2 - Blit the graph vertically mirrored. B_TRANSLUCENT - 4 - Blit the graph with half transparency. B_ALPHA - 8 - Blit the graph in some way. (What does this do exactly?) B_ABLEND - 16 - Blit the graph using additive blending (nice effect for fire). B_SBLEND - 32 - Blit the graph using subtractive blending (nice effect for ghosting). B_NOCOLORKEY - 128 - Blit the transparent parts of the graph as black.

These are all single unique cases and can be combined to form different unique cases. For example, when we want a translucent, horizontally mirrored blit operation with use of additive blending, we would do:

```B_HMIRROR | B_TRANSLUCENT | B_ABLEND
1         | 4             | 16       = 21
```

Because the bits are unique, the addition operator can also be used. But when we consider there would be a constant called B_HVMIRROR, which has the value B_HMIRROR|B_VMIRROR (3), the addition operator can't be used all the time:

```B_HMIRROR | B_HVMIRROR == 1 | 3 == 3
B_HMIRROR + B_HVMIRROR == 1 + 3 == 4
```

In conclusion, use the bor operator when dealing with bit flags to be on the safe side.

### Usage Example

```Process main()
Private
unsigned byte options;
Begin

/* Manipulate bit flags */

// To set options, use = (the bits with 1's will be targeted)
options = 01000001b;

// To add options, use | (the bits with 1's will be targeted)
options |= 00000001b;

// To remove options, use & and ~ (the bits with 1's will be targeted)
options &= ~00010000b;
// same: options &= 11101111h (the bits with 0's will be targeted)

// To switch options, use ^ (the bits with 1's will be targeted)
options ^= 10000000b;

/* Manipulate bit flags using the << operator (these are equivalent to the last three) */

options|= 1<<0; // position 0 is now ON
options&= ~(1<<4); // position 4 is now OFF
options^= (1<<7); // position 7 is now SWITCHED

/* Checking of bit flags */

// Check if a certain option is set (the bits with 1's will be checked)
if((options&10000000b)==10000000b)
end

// Check if a certain option is not set (the bits with 1's will be checked)
if((options&10000000b)==0)
end

// Check if multiple options are set (the bits with 1's will be checked)
if((options&10000001b)==10000001b)
end

// Check if multiple options are not set (the bits with 1's will be checked)
if((options&00000110b)==0)
end

// Check if at least one of multiple options is set (the bits with 1's will be checked)
if((options&00000110b)!=0)
end

// Check if at least one of multiple options is not set (the bits with 1's will be checked)
if((options&00000110b)!=00000110b)
end

/* Checking of bit flags using the << operator */

// Check if a certain option is set
if((options&(1<<7))==(1<<7)) // position 7 is ON
end

// Check if a certain option is not set
if((options&(1<<7))==0) // position 7 is OFF
end

End
```

Used in example: Bitwise Operators