Bytes and data-types | Delphi programming

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Bytes and data-types | Delphi programming | mortenbs.com
Last updated Jan 2012.

A byte is an unsigned number in the range [0..255] (256 possible values).

Different ways to observe a byte

System	Range
Decimal	0..255
Hexadecimal	00..FF
Binary	00000000..11111111

Data types based on a range of bytes

Data type	Type	Size	Description	Range
Char	fixed	1 byte	Ansi char	#0..#255 ($00..$FF)
Word	fixed	2 bytes	16-Bit unsigned	0..65535 ($0000..$FFFF)
SmallInt	fixed	2 bytes	16-Bit signed	-32768..32767 ($0000..$FFFF)
LongWord (cardinal)	fixed	4 bytes	32-Bit unsigned	0..4294967295 ($00000000..$FFFFFFFF)
LongInt (integer)	fixed	4 bytes	32-Bit signed	-2147483648..2147483647 ($00000000..$FFFFFFFF)
Int64	fixed	8 bytes	64-Bit signed	-9223372036854775808..9223372036854775807
Single	fixed	4 bytes	float
Double	fixed	8 bytes	float
Extended	fixed	10 bytes	float
String	dynamic	length(s)+1	NULL terminated (#0)

Table of bits

Bit	Hex	Bytes	Value/ID	Combinations
1	$01	<1	$00000001	2
2	$02	<1	$00000002	4
3	$03	<1	$00000004	8
4	$04	<1	$00000008	16
5	$05	<1	$00000010	32
6	$06	<1	$00000020	64
7	$07	<1	$00000040	128
8	$08	1	$00000080	256
9	$09	<2	$00000100	512
10	$0A	<2	$00000200	1.024
11	$0B	<2	$00000400	2.048
12	$0C	<2	$00000800	4.096
13	$0D	<2	$00001000	8.192
14	$0E	<2	$00002000	16.384
15	$0F	<2	$00004000	32.768
16	$10	2	$00008000	65.536
17	$11	<3	$00010000	131.072
18	$12	<3	$00020000	262.144
19	$13	<3	$00040000	524.288
20	$14	<3	$00080000	1.048.576
21	$15	<3	$00100000	2.097.152
22	$16	<3	$00200000	4.194.304
23	$17	<3	$00400000	8.388.608
24	$18	3	$00800000	16.777.216
25	$19	<4	$01000000	33.554.432
26	$1A	<4	$02000000	67.108.864
27	$1B	<4	$04000000	134.217.728
28	$1C	<4	$08000000	268.435.456
29	$1D	<4	$10000000	536.870.912
30	$1E	<4	$20000000	1.073.741.824
31	$1F	<4	$40000000	2.147.483.648
32	$20	4	$80000000	4.294.967.296

There is 8 bits of one byte.
Each bit has a value/ID: 1+2+4+8+16+32+64+128 = 256
Minimum value is ZERO: 256¹-1 = [0..255]

For obtaining higher numbers than 255, multiple bytes is combined for having more total bits available.
Using two bytes there is total 16 bits: (256*256) = 65536 possible values.

Type conversions

ch:=ansiChar(b); //Byte to char
b:=byte(ch); //Char to byte

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An example of reading the 8 bits from a single byte:

procedure byteToBits(aByte:byte;out b1,b2,b3,b4,b5,b6,b7,b8:boolean);
begin
b1:=  1 and aByte<>0;
b2:=  2 and aByte<>0;
b3:=  4 and aByte<>0;
b4:=  8 and aByte<>0;
b5:= 16 and aByte<>0;
b6:= 32 and aByte<>0;
b7:= 64 and aByte<>0;
b8:=128 and aByte<>0
end;

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An example of defining the 8 bits in a single byte:

function bitsToByte(b1,b2,b3,b4,b5,b6,b7,b8:boolean):byte;
begin
if b1 then result:=1 else result:=0;
if b2 then inc(result,2);
if b3 then inc(result,4);
if b4 then inc(result,8);
if b5 then inc(result,16);
if b6 then inc(result,32);
if b7 then inc(result,64);
if b8 then inc(result,128)
end;

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In some cases the TBits class is very useful:

uses
classes;

//...

function bitsToByte(aBits:tBits):byte;
const n:array[0..7] of byte=(1,2,4,8,16,32,64,128);
var b:byte;
begin result:=0;
for b:=0 to 7 do if aBits[b] then inc(result,n[b])
end;

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See also

Delphi programming - Basics, Components, links...

IT - IT/Technology. Various projects and information about computer technology and electronic...

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