_BYTE - QB64Official/qb64 GitHub Wiki
A _BYTE variable can hold signed variable values from -128 to 127 (one byte or 8 _BITs). _UNSIGNED from 0 to 255.
- 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.
-
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.
- 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.
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.