tianh notes

 如果输入是 n bits，base64 编码后得到的是 ceil(n/6) Bytes = ceil(4n/3) bits。也就是说，base64 后会膨胀 [4/3, 8] 倍，在输入足够长的情况下可以看作 4/3。 base64 index Index Binary Char Index Binary Char Index Binary Char Index Binary Char 0 000000 A 16 010000 Q 32 100000 g 48 110000 w 1 000001 B 17 010001 R 33 100001 h 49 110001 x 2 000010 C 18 010010 S 34 100010 i 50 110010 y 3 000011 D 19 010011 T 35 100011 j 51 110011 z 4 000100 E 20 010100 U 36 100100 k 52 110100 0 5 000101 F 21 010101 V 37 100101 l 53 110101 1 6 000110 G 22 010110 W 38 100110 m 54 110110 2 7 000111 H 23 010111 X 39 100111 n 55 110111 3 8 001000 I 24 011000 Y 40 101000 o 56 111000 4 9 001001 J 25 011001 Z 41 101001 p 57 111001 5 10 001010 K 26 011010 a 42 101010 q 58 111010 6 11 001011 L 27 011011 b 43 101011 r 59 111011 7 12 001100 M 28 011100 c 44 101100 s 60 111100 8 13 001101 N 29 011101 d 45 101101 t 61 111101 9 14 001110 O 30 011110 e 46 101110 u 62 111110 + 15 001111 P 31 011111 f 47 101111 v 63 111111 / Padding =

Ref : https://en.m.wikipedia.org/wiki/English-language_vowel_changes_before_historic_/r/#Hurry.E2.80.93furry_merger The hurry–furry merger occurs when the vowel /ʌ/ before intervocalic /r/ is merged with /ɜ/. That is particularly a feature in many dialects of North American English. Speakers with the merger pronounce hurry to rhyme with furry and turret to rhyme with stir it.  To occur, the merger requires the nurse mergers (cure-nurse merger) to be in full effect, which is the case outside the British Isles. In Scotland, hurry /ˈhʌre/ is a perfect rhyme of furry /ˈfʌre/, but there is no merger since the vowel /ɜ/ has never developed because of the lack of nurse mergers. That means that STRUT, DRESS and KIT can all occur before both intervocalic and coda /r/ and so fur, fern, and fir have distinct vowels: /fʌr, fɛrn, fɪr/.

Phonetics 语音学，研究人的语音的具象特征，和语音的用途、意义无关。也和特定语言无关。 Phonology 音系学，也作音韵学，研究特定语言的语音，侧重语音的功能。 Historical Chinese Phonology 汉语音韵学，也作音韵学，研究汉语的历史语音变化。