Difference between revisions of "BIT"

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{{DISPLAYTITLE:_BIT}}
#REDIRECT [[Data Types]]
The '''_BIT''' datatype can return only values of 0 (bit off) and -1 (bit on).
 
 
{{PageSyntax}}
:: [[DIM]] variable AS [_UNSIGNED] '''_BIT''' [* numberofbits]
 
 
:: [[_DEFINE]] Letter[-Range|,...] AS [_UNSIGNED] '''_BIT''' [* numberofbits]
 
 
''More information:''
 
* 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 currently 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 shifted tilde key! '''NOT an apostrophy'''! Foreign keyboards may not have the ´ key. Try [[CHR$]](96).
 
:You can define a bit on-the-fly by adding a ` after the variable, like this; variable` = -1
 
:If you want a unsigned bit you can define it on-the-fly by adding ~` instead, like this; variable~` = 1
 
:You can set the number of bits on the fly by just adding that number - this defines it as being two bits; variable`2 = -1
 
 
<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. 
 
 
''Example:'' Shifting bits in a value.
{{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]]
* [[_DEFINE]], [[_UNSIGNED]]
* [[DIM]]
* [[Binary]], [[Boolean]]
* [[Variable Types]]
* [[Converting Bytes to Bits]]
 
 
{{PageNavigation}}

Revision as of 16:02, 18 July 2017

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