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IdCoderXXE.pas
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Contains classes, constants, and variables used to implement encoders and decoders for the XXEncode encoding scheme.

Description

IdCoderXXE.pas contains classes, constants, and variables used to implement encoders and decoders for the XXEncode encoding scheme. The XXEncode encoding scheme is used to convert binary data into a 7-bit textual representation, and is very simular to the UUEncode encoding scheme. 

XXEncode, like Base64, is an encoding mechanism designed to represent arbitrary sequences of byte data in a form that need not be humanly readable. XXEncode was designed as a replacement for an earlier version of UUEncode, which contained an encoding error. XXEncode is little used since the UUEncode alphabet has been enhanced. 

XXEncode encoding represents 24-bit groups of input as output strings of 4 encoded characters. Proceeding from left to right, a 24-bit input group is formed by concatenating 3 8bit input groups. These 24 bits are then treated as 4 concatenated 6-bit groups, each of which is translated into a single digit in the XXEncode alphabet. 

XXEncode differs from Base64 and UUEncode in that it utilizes a different coding table, or alphabet, to represent the encoded output values. The XXEncode Alphabet contains the following encodings and values: 

 

Value 
Encoding 
0 
+ 
1 
- 
2 
0 
3 
1 
4 
2 
5 
3 
6 
4 
7 
5 
8 
6 
9 
7 
10 
8 
11 
9 
12 
A 
13 
B 
14 
C 
15 
D 
16 
E 
17 
F 
18 
G 
19 
H 
20 
I 
21 
J 
22 
K 
23 
L 
24 
M 
25 
N 
26 
O 
27 
P 
28 
Q 
29 
R 
30 
S 
31 
T 
32 
U 
33 
V 
34 
W 
35 
X 
36 
Y 
37 
Z 
38 
a 
39 
b 
40 
c 
41 
d 
42 
e 
43 
f 
44 
g 
45 
h 
46 
i 
47 
j 
48 
k 
49 
l 
50 
m 
51 
n 
52 
o 
53 
p 
54 
q 
55 
r 
56 
s 
57 
t 
58 
u 
59 
v 
60 
w 
61 
x 
62 
y 
63 
z 
See Also
Classes
 
Name 
Description 
 
TIdDecoderXXE 
Implements a decoder for data encoded using the XXEncode algorithm and the XXEncode alphabet. 
 
TIdEncoderXXE 
Implements support for the XXEncode alphabet and the XXEncode algorithm. 
Constants
Name 
Description 
GXXECodeTable 
Represents valid characters and their ordinal position in the XXEncode alphabet. 
Variables
Name 
Description 
GXXEDecodeTable 
Identifies the decoding table used by TIdDecoderXXE for the XXEncode alphabet. 
Legend
 
Class 
Internet Direct (Indy) version 10.1.5
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