ios--Algorithm--BASE64 Chapter

As a common standard of string transcoding in various languages, Base64 is loved by programmers.

To introduce: The BASE64 encoding requires 3 8-bit bytes (3*8=24) to be converted to 4 6-bit bytes (4*6=24), followed by 6-bit two, to form 0-bit bytes. If the remaining characters are less than 3 bytes, then the 0 padding, the output character using ' = ', so the text output after encoding may appear 1 or 2 ' = '

In order to ensure the output of the encoded bit readable characters, BASE64 developed a coding table for unified conversion. The size of the encoded table is 2^6=64, which is also the origin of the Base64 name.

Base64 Coding Table

Code Value	character		Code Value	character		Code Value	character		Code Value	character
0	A	16	Q	32	G	48	W
1	B	17	R	33	H	49	X
2	C	18	S	34	I	50	Y
3	D	19	T	35	J	51	Z
4	E	20	U	36	K	52	0
5	F	21st	V	37	L	53	1
6	G	22	W	38	M	54	2
7	H	23	X	39	N	55	3
8	I	24	Y	40	O	56	4
9	J	25	Z	41	P	57	5
10	K	26	A	42	Q	58	6
11	L	27	B	43	R	59	7
12	M	28	C	44	S	60	8
13	N	29	D	45	T	61	9
14	O	30	E	46	U	62	+
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