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Visualizaçõesencode ASCII symbols into UTF-8 presentation
I have a string that I k'now for sure has only ASCII lettes.
JS treats strings as UTF-8 by default,
so it means that every character takes up to 4 bytes,
which is 4 times ASCII.
I'm trying to compress / save spaces / get the shortest string as possible,
by having an encode and decode functions.
I thought about representing 4 characters of ASCII on a UTF-8 string and by that achieve my goals, is there anything like that?
If not, what is the best way to compress ASCII strings, so that by encoding and decoding I'll reach the same string?
2 Respostas
Responde à pergunta0
Actually JavaScript encodes program strings in UTF-16, which uses 2 octets (16 bits) for Unicode characters in the BMP (Basic Multilingual Plane) and 4 octets (32 bits) for characters outside it. So internally at least, ASCII characters use 2 bytes.
There is room to pack two ASCII characters into 16 bits since they only use 7 bits each. Furthermore, since the difference between 2**16 and 2**14 is 49152, and the number of encodings used by surrogate pairs in UTF-16 is (allegedly) 2048, you should be able to devise an encoding scheme that avoids the range of code points used by surrogates.
You could also use 8 bit typed arrays to hold ASCII characters while avoiding the complexity of a custom compression algorithm.
The purpose of compressing 7 bit ASCII for use within JavaScript is largely (entirely?) academic these days and not something there is a demand for. Note that encoding 7 bit ASCII content into UTF-8 (for transmission or file encoding) only uses one byte for ASCII characters due to the design of UTF-8.