QB64-PE/internal/help/_BIT.txt

{{DISPLAYTITLE:_BIT}}
The [[_BIT]] datatype can return only values of 0 (bit off) and -1 (bit on). 


{{PageSyntax}}
: [[DIM]] {{Parameter|variable}} [[AS]] [{{KW|_UNSIGNED}}] [[_BIT]] [* {{Parameter|numberofbits}}]

: [[_DEFINE]] {{Parameter|Letter}}[{{Parameter|-Range}}|,...] [[AS]] [{{KW|_UNSIGNED}}] [[_BIT]] [* {{Parameter|numberofbits}}]


{{PageDescription}}
* An [[_UNSIGNED]] _BIT can hold 0 or 1 instead of 0 and -1, if you set the numberofbits you can hold larger values depending on the number of bits you have set (_BIT * 8 can hold the same values as [[_BYTE]] for example) and the information below is compromised if setting any number of bits other than 1.
* If you set the variable to any other number then the least significant bit of that number will be set as the variables number, if the bit is 1 (on) then the variable will be -1 and if the bit is 0 (off) then the variable will be 0.
*The least significant bit is the last bit on a string of bits (11111) since that bit will only add 1 to the value if set. The most significant bit is the first bit on a string of bits and changes the value more dramatically (significantly) if set on or off.
*The _BIT datatype can be succesfully used as a [[Boolean]] (TRUE or FALSE) and it requires minimal amount of memory (the lowest amount possible actually, one byte can hold 8 bits, if you want to use bits in order to decrease memory usage, use them as arrays as a _BIT variable by itself allocates 4 bytes - DIM bitarray(800) AS _BIT uses 100 bytes).
* '''When a variable has not been assigned or has no type suffix, the value defaults to [[SINGLE]].'''
* '''[[Keywords_currently_not_supported_by_QB64|_BIT is not supported in User Defined TYPES.]]''' Use a [[_BYTE]] and assign up to 8 bit values as shown below.


*'''Suffix Symbols''' The [[_BIT]] type suffix used is below the grave accent (`), usually located under the tilde (~) key (not an apostrophe). Foreign keyboards may not have the ` key. Try Alt+96 in the IDE.

:You can define a bit on-the-fly by adding a ` after the variable, like this: {{InlineCode}}variable` = -1{{InlineCodeEnd}}

:If you want an unsigned bit you can define it on-the-fly by adding ~` instead, like this: {{InlineCode}}variable~` = 1{{InlineCodeEnd}}

:You can set the number of bits on the fly by just adding that number - this defines it as being two bits: {{InlineCode}}variable`2 = -1{{InlineCodeEnd}}


<center>'''[[_BIT|BITS]]'''</center>
* The '''MSB''' is the most significant(largest) bit value and '''LSB''' is the least significant bit of a binary or register memory address value. The order in which the bits are read determines the binary or decimal byte value. There are two common ways to read a byte:

:* '''"Big-endian"''': MSB is the first bit encountered, decreasing to the LSB as the last bit by position, memory address or time.
:* '''"Little-endian"''': LSB is the first bit encountered, increasing to the MSB as the last bit by position, memory address or time.
{{WhiteStart}}
         '''Offset or Position:    0    1   2   3   4   5   6   7      Example: 11110000'''
                              ----------------------------------             --------
    '''Big-Endian Bit On Value:'''   128  64  32  16   8   4   2   1                 240
 '''Little-Endian Bit On Value:'''    1    2   4   8  16  32  64  128                 15
{{WhiteEnd}}
::The big-endian method compares exponents of 2 <sup>7</sup> down to 2 <sup>0</sup> while the little-endian method does the opposite. 

<center>'''[[_BYTE|BYTES]]'''</center>
* [[INTEGER]] values consist of 2 bytes called the '''HI''' and '''LO''' bytes. Anytime that the number of binary digits is a multiple of 16 (2bytes, 4 bytes, etc.) and the HI byte's MSB is on(1), the value returned will be negative. Even with [[SINGLE]] or [[DOUBLE]] values! 
{{WhiteStart}}                                 '''16 BIT INTEGER OR REGISTER'''
              '''AH (High Byte Bits)                         AL (Low Byte Bits)'''
   BIT:    15    14   13   12   11   10   9   8  |   7   6    5   4    3    2   1    0
          ---------------------------------------|--------------------------------------
   HEX:   8000  4000 2000 1000  800 400  200 100 |  80   40  20   10   8    4   2    1
                                                 |
   DEC: -32768 16384 8192 4096 2048 1024 512 256 | 128   64  32   16   8    4   2    1
{{WhiteEnd}}
::The HI byte's '''MSB''' is often called the '''sign''' bit! When all 16 of the integer binary bits are on, the decimal return is -1.  


{{PageExamples}}
''Example:'' Shifting bits in a value in QB64 versions prior to 1.3 (you can use [[_SHL]] and [[_SHR]] starting with version 1.3).
{{CodeStart}} '' ''
n = 24
Shift = 3

{{Cl|PRINT}} LShift(n, Shift)
{{Cl|PRINT}} RShift(n, Shift)
{{Cl|END}}

{{Cl|FUNCTION}} LShift&(n AS {{Cl|LONG}}, LS AS {{Cl|LONG}})
IF LS < 0 THEN {{Cl|EXIT FUNCTION}}
LShift = {{Cl|INT}}(n * (2 ^ LS))    
{{Cl|END FUNCTION}}

{{Cl|FUNCTION}} RShift&(n AS {{Cl|LONG}}, RS AS {{Cl|LONG}})
IF RS < 0 THEN {{Cl|EXIT FUNCTION}}
RShift = {{Cl|INT}}(n / (2 ^ RS))
{{Cl|END FUNCTION}} '' ''
{{CodeEnd}}
{{small|Adapted from code by RThorpe}}
{{OutputStart}} 192
 3
{{OutputEnd}}


{{PageSeeAlso}} 
* [[&B]] (binary), [[_BYTE]]
* [[_SHL]], [[_SHR]]
* [[_DEFINE]], [[_UNSIGNED]]
* [[DIM]]
* [[Binary]], [[Boolean]]
* [[Variable Types]]
* [[Converting Bytes to Bits]]


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