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_BYTE

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


Contents

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 2 7 down to 2 0 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!

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



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