JS Base64 turn Binary

Base64 Coding Rules

1. Turn 3 characters into 4 characters.
2, every 76 characters multibyte a newline character.
3, the last Terminator also to deal with.
Conversion before 11111101, 11111111, 11111111 (binary)
Converted 00111111, 00011111, 00111111, 00111111 (binary, because the base64 only need 6 bits to be satisfied, but a byte is 8 bits, so more than 2 useless 0)

To go back to 2, you need to cut the front 00 and let the data come up.

The first approach: using ToString (2) to convert to 2 binary strings, and then splicing, but the binary data too much, the direct operation of memory is much faster, so the string is no longer used.

A second approach:

Base64 encoded Table Const MAP = {"0": 1, "2":, "3": +, "4": "5":, "6": "7": 8 ":," 9 "," A ": 0 , "B": 1, "C": 2, "D": 3, "E": 4, "F": 5, "G": 6, "H": 7, "I": 8, "J": 9, "K": Ten, "L": One, "M": A, "N": "O": "P"  :, "Q": +, "R": +, "S": +, "T": +, "U": +, "V": +, "W": "X": +, "Y":, "Z": +, "a": +, "B":, "C": 28,  "D": "E": +, "F": +, "G": +, "H": "I":, "J": +, "K": +, "L": Panax Notoginseng, "M": Max, "n": G, "O": +, "P": KT, "Q": "R": A, "s": "," "T": "G", "U": +, "V": +, "w": ×, "X": $, "y": +, "Z": Wuyi, "+": +, "/":}function Base64to2 (base64) {Let Len = base64.length *. 75//Convert to Int8array required length base64 = Base64.replace (/=*$/, ")//Remove = (placeholder) Const INT8 =    New Int8array (LEN)//Set Int8array view let arr1, ARR2, ARR3, ARR4, p = 0for (Let i = 0; i < base64.length; i + = 4) { ARR1 = Map[base64[i]]//each cycle converts base644 bytes to 3 int8array Direct ARR2 = Map[base64[i + 1]] Arr3 = Map[base64[i + 2]] ar R4 = Map[base64[i + 3]] Suppose data arr data 00101011 00101111 00110011 00110001 int8[p++] = arr1 << 2 | ARR2 >> 4//upper action arr1 move left 2 bits to 10101100//ARR2 to right 4 bits: 00000010//| For ' and ' Operation: 10101110 int8[p++] = arr2 << 4 | ARR3 >> 2 int8[p++] = ARR3 << 6 | ARR4} return int8}

　　

JS Base64 turn Binary