_BYTE

A _BYTE variable can hold signed variable values from -128 to 127 (one byte or 8 _BITs). Unsigned from 0 to 255.

Syntax

DIM byte AS [[[_UNSIGNED]]] _BYTE

Description

• Signed _BYTE values can range from -128 to 127.
• _UNSIGNED _BYTEs can hold values from 0 to 255. _UNSIGNED expands the range of positive values.
• Can be defined in a QB64 _DEFINE statement using a starting letter range of variable names.
• Also can be used in a subroutine parameter AS _BYTE variable definitions.
• Define a byte using the suffix %% after the variable name: variable%% = -54
• Define an unsigned byte by adding the suffix ~%% after the variable name: variable~%% = 54
• When a variable has not been assigned or has no type suffix, the value defaults to SINGLE.

BITS

• 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.

        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

The big-endian method compares exponents of 2⁷ down to 2⁰ while the little-endian method does the opposite.

BYTES

• 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!

Template: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

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.

Examples

How negative assignments affect the _UNSIGNED value returned by a byte (8 bits).

DIM unsig AS _UNSIGNED _BYTE DIM sig AS _BYTE CLS unsig = 1 sig = 1 PRINT "00000001 = unsigned & signed are both" + STR$(unsig AND sig) unsig = 127 sig = 127 PRINT "&B01111111 = unsigned & signed are both" + STR$(unsig AND sig) unsig = 255 sig = 255 PRINT "&B11111111 = unsigned is" + STR$(unsig) + " but signed is " + STR$(sig) unsig = 254 sig = 254 PRINT "&B11111110 = unsigned is" + STR$(unsig) + " but signed is " + STR$(sig) unsig = 253 sig = 253 PRINT "&B11111101 = unsigned is" + STR$(unsig) + " but signed is " + STR$(sig) PRINT PRINT "The signed value needs the MSB bit for the sign." PRINT "The most significant bit is furthest to the left."

&B00000001 = unsigned & signed are both 1 &B01111111 = unsigned & signed are both 127 &B11111111 = unsigned is 255 but signed is -1 &B11111110 = unsigned is 254 but signed is -2 &B11111101 = unsigned is 253 but signed is -3 The signed value needs the MSB bit for the sign. The most significant bit is furthest to the left.

See also

• _BIT, &B
• _DEFINE, DIM
• _UNSIGNED
• _SHL, _SHR
• Mathematical Operations
• Screen Memory
• Variable Types
• Converting Bytes to Bits

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