Base91 (stylized as basE91) is a type of encoding scheme that represent binary data in an ASCII string format
As the name implies, basE91 uses radix-91 to encode data using the below table (the first column is the digit value, the next two column is the character and its ASCII value)
0 A 0x41 13 N 0x4E 26 a 0x61 39 n 0x6E 52 0 0x30 65 % 0x25 78 > 0x3E
1 B 0x42 14 O 0x4F 27 b 0x62 40 o 0x6F 53 1 0x31 66 & 0x26 79 ? 0x3F
2 C 0x43 15 P 0x50 28 c 0x63 41 p 0x70 54 2 0x32 67 ( 0x28 80 @ 0x40
3 D 0x44 16 Q 0x51 29 d 0x64 42 q 0x71 55 3 0x33 68 ) 0x29 81 [ 0x5B
4 E 0x45 17 R 0x52 30 e 0x65 43 r 0x72 56 4 0x34 69 * 0x2A 82 ] 0x5D
5 F 0x46 18 S 0x53 31 f 0x66 44 s 0x73 57 5 0x35 70 + 0x2B 83 ^ 0x5E
6 G 0x47 19 T 0x54 32 g 0x67 45 t 0x74 58 6 0x36 71 , 0x2C 84 _ 0x5F
7 H 0x48 20 U 0x55 33 h 0x68 46 u 0x75 59 7 0x37 72 . 0x2E 85 ` 0x60
8 I 0x49 21 V 0x56 34 i 0x69 47 v 0x76 60 8 0x38 73 / 0x2F 86 { 0x7B
9 J 0x4A 22 W 0x57 35 j 0x6A 48 w 0x77 61 9 0x39 74 : 0x3A 87 | 0x7C
10 K 0x4B 23 X 0x58 36 k 0x6B 49 x 0x78 62 ! 0x21 75 ; 0x3B 88 } 0x7D
11 L 0x4C 24 Y 0x59 37 l 0x6C 50 y 0x79 63 # 0x23 76 < 0x3C 89 ~ 0x7E
12 M 0x4D 25 Z 0x5A 38 m 0x6D 51 z 0x7A 64 $ 0x24 77 = 0x3D 90 " 0x22
The data stream is split into 13-bit chunks, which are then converted into two characters. The maximum value of the chunk is 213 - 1 = 8191 so it can be stored in a two-digit radix-91 value whose maximum is 912 = 8281
More information:
