中国DOS联盟

After calculating the encoded result after base64 conversion, it is also necessary to correspond to the relevant characters:

A ----------- 0
B ----------- 1
C ----------- 2
D ----------- 3
E ----------- 4
F ----------- 5
G ----------- 6
H ----------- 7
I ----------- 8
J ----------- 9
K ----------- 10
L ----------- 11
M ----------- 12
N ----------- 13
O ----------- 14
P ----------- 15
Q ----------- 16
R ----------- 17
S ----------- 18
T ----------- 19
U ----------- 20
V ----------- 21
W ----------- 22
X ----------- 23
Y ----------- 24
Z ----------- 25
a ----------- 26
b ----------- 27
c ----------- 28
d ----------- 29
e ----------- 30
f ----------- 31
g ----------- 32
h ----------- 33
i ----------- 34
j ----------- 35
k ----------- 36
l ----------- 37
m ----------- 38
n ----------- 39
o ----------- 40
p ----------- 41
q ----------- 42
r ----------- 43
s ----------- 44
t ----------- 45
u ----------- 46
v ----------- 47
w ----------- 48
x ----------- 49
y ----------- 50
z ----------- 51
0 ----------- 52
1 ----------- 53
2 ----------- 54
3 ----------- 55
4 ----------- 56
5 ----------- 57
6 ----------- 58
7 ----------- 59
8 ----------- 60
9 ----------- 61
+ ----------- 62
/ ----------- 63

The time for all experts to show their skills has come.

Base64 encoding is quite useful, for example, in eml files, embedding bin in batch scripts, etc.

Last edited by electronixtar on 2006-10-20 at 01:08 ]

Can you tell us about the bitwise operations in set/a?

Originally posted by lxmxn at 2006-10-19 07:04:

　　Thanks to brother est for writing the post about bit operations.

　　But it didn't write out in which aspects these bit operations are applied, which can't arouse everyone's interest in bit operations. Everyone only knows vaguely...

This idea is good~ : )
Write some examples of bit operations that can arouse everyone's interest and are practical~ : )
It can both gather popularity, lay the foundation for development, and expand the knowledge scope~ : )

To be honest, I just copied the bitwise operations from other languages and changed them to set /a. There's really nothing to write about.

//////
We are looking forward to it.

Hehe, that really hits the nail on the head

This is my study record, and the bit operations are written in detail:

LZ, you need to first understand the conversion between decimal and binary, etc.

I'll give a few simple examples to explain bit operations under CMD:
set /a 13^<^<1
The result is 26, because the binary of 13 is 1101. Shifting left by 1 bit is equivalent to adding a 0 at the end of the binary, which is 11010, that is 26.
set /a 13^>^>1
The result is 6. Removing the last bit 1 from 1101 gives 110, which is 10 in decimal 6.

Similarly
set /a 13^<^<2 is 52
set /a 13^>^>2 is 3

Then talk about bitwise AND &
The meaning of bitwise AND is that after converting to binary, the bits are operated logically AND. The algorithm of AND operation is that it's 1 only if all are 1, otherwise 0.
set /a 13^&11
The result is 9
Because 1101&1011, there are 0s in the middle two bits. Only the first and last bits are both 1, so it's 1001, that is 10 in decimal 9.

After understanding that bit operations are bit-corresponding operations, there's no need to go into details about XOR and OR. Just say the algorithms of XOR and OR.

XOR is also called exclusive OR (there is also equivalence). The algorithm is that the result is 0 if two numbers are the same, and 1 if different, that is 0^1=1, 1^1=0, 0^0=0.
And the OR operation is that it's 0 only if all are 0, that is 0|1=1, 1|1=1, 0|0=0.

@echo off
set b=0
for /l %%a in (1,1,100) do set /a b=b+%%a>>nul
echo The sum from 1 to 100 is: %b%
pause>nul
Experts:
What does "set /a a=00000010 << 2" mean?