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104 lines
4.5 KiB
Plaintext
104 lines
4.5 KiB
Plaintext
{{DISPLAYTITLE:_BYTE}}
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A [[_BYTE]] variable can hold signed variable values from -128 to 127 (one byte or 8 [[_BIT]]s). [[_UNSIGNED|Unsigned]] from 0 to 255.
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{{PageSyntax}}
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: [[DIM]] {{Parameter|byte}} [[AS]] [[[_UNSIGNED]]] [[_BYTE]]
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{{PageDescription}}
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* Signed _BYTE values can range from -128 to 127.
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* [[_UNSIGNED]] _BYTEs can hold values from 0 to 255. [[_UNSIGNED]] expands the range of positive values.
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* Can be defined in a '''QB64''' [[_DEFINE]] statement using a starting letter range of variable names.
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* Also can be used in a subroutine parameter [[AS]] _BYTE variable definitions.
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* Define a byte using the suffix %% after the variable name: {{Parameter|variable%%}} = -54
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* Define an unsigned byte by adding the suffix ~%% after the variable name: variable~%% = 54
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* '''When a variable has not been assigned or has no type suffix, the value defaults to [[SINGLE]].'''
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<center>'''[[_BIT|BITS]]'''</center>
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* 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:
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:* '''"Big-endian"''': MSB is the first bit encountered, decreasing to the LSB as the last bit by position, memory address or time.
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:* '''"Little-endian"''': LSB is the first bit encountered, increasing to the MSB as the last bit by position, memory address or time.
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{{WhiteStart}}
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'''Offset or Position: 0 1 2 3 4 5 6 7 Example: 11110000'''
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---------------------------------- --------
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'''Big-Endian Bit On Value:''' 128 64 32 16 8 4 2 1 240
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'''Little-Endian Bit On Value:''' 1 2 4 8 16 32 64 128 15
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{{WhiteEnd}}
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::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.
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<center>'''[[_BYTE|BYTES]]'''</center>
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* [[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!
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{{WhiteStart}} '''16 BIT INTEGER OR REGISTER'''
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'''AH (High Byte Bits) AL (Low Byte Bits)'''
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BIT: 15 14 13 12 11 10 9 8 | 7 6 5 4 3 2 1 0
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---------------------------------------|--------------------------------------
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HEX: 8000 4000 2000 1000 800 400 200 100 | 80 40 20 10 8 4 2 1
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DEC: -32768 16384 8192 4096 2048 1024 512 256 | 128 64 32 16 8 4 2 1
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{{WhiteEnd}}
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::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.
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{{PageExamples}}
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:How negative assignments affect the _UNSIGNED value returned by a byte (8 bits).
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{{CodeStart}}
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{{Cl|DIM}} unsig {{Cl|AS}} {{Cl|_UNSIGNED}} {{Cl|_BYTE}}
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{{Cl|DIM}} sig {{Cl|AS}} {{Cl|_BYTE}}
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{{Cl|CLS}}
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unsig = 1
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sig = 1
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{{Cl|PRINT}} "00000001 = unsigned & signed are both" + {{Cl|STR$}}(unsig {{Cl|AND}} sig)
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unsig = 127
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sig = 127
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{{Cl|PRINT}} "&B01111111 = unsigned & signed are both" + {{Cl|STR$}}(unsig {{Cl|AND}} sig)
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unsig = 255
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sig = 255
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{{Cl|PRINT}} "&B11111111 = unsigned is" + {{Cl|STR$}}(unsig) + " but signed is " + {{Cl|STR$}}(sig)
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unsig = 254
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sig = 254
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{{Cl|PRINT}} "&B11111110 = unsigned is" + {{Cl|STR$}}(unsig) + " but signed is " + {{Cl|STR$}}(sig)
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unsig = 253
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sig = 253
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{{Cl|PRINT}} "&B11111101 = unsigned is" + {{Cl|STR$}}(unsig) + " but signed is " + {{Cl|STR$}}(sig)
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{{Cl|PRINT}}
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{{Cl|PRINT}} "The signed value needs the MSB bit for the sign."
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{{Cl|PRINT}} "The most significant bit is furthest to the left."
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{{CodeEnd}}
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{{OutputStart}}
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&B00000001 = unsigned & signed are both 1
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&B01111111 = unsigned & signed are both 127
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&B11111111 = unsigned is 255 but signed is -1
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&B11111110 = unsigned is 254 but signed is -2
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&B11111101 = unsigned is 253 but signed is -3
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The signed value needs the MSB bit for the sign.
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The most significant bit is furthest to the left.
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{{OutputEnd}}
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{{PageSeeAlso}}
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* [[_BIT]], [[&B]]
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* [[_DEFINE]], [[DIM]]
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* [[_UNSIGNED]]
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* [[_SHL]], [[_SHR]]
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* [[Mathematical Operations]]
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* [[Screen Memory]]
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* [[Variable Types]]
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* [[Converting Bytes to Bits]]
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{{PageNavigation}}
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<
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