String representation in erlang
Tue Sep 13 19:46:53 CEST 2005
Yes, 8 bytes for a single character is hideously too long. You can
encode any character on the planet with only 4 bytes. You can use
variable byte encoding to further reduce overall length for complex
languages. I would like to see these types of things corrected one day.
Until then, I'll settle for understanding binary strings better. ;-)
I understand the basic form: <<"abcde">>. What I don't understand is if
this works with multi-byte (in particular variable-byte) encoding
schemes (utf-8, 16, etc...). Does the binary string only work for 8 bit
characters? ...any examples of other use?
I think the kind of code example missing is something with Chinese (or
pick your complex language) and English characters in the same "string",
allow a user to enter the string into a yaws web form and stores the
"string" in erlang and then redisplays the string. For binary strings,
I don't even know where to start with this simple task.
thanks, ke han
hinus Pollard wrote:
> Hi there
> According to the Erlang efficiency guide a string is internally represented as
> a list of integers, thus consuming 2 words (8 bytes on a 32bit platform) of
> memory *per* character.
> The attached code is an attempt at reducing the memory footprint of strings in
> erlang (passing between functions etc etc).
> The basic idea is to pack a string into n byte sized integers and unpacking
> them on the other side. The text file called compare.txt also shows the
> memory needed to represent strings in normal erlang strings and this string
> Normal erlang strings are 2 words/character. The packed representation uses 1
> word of memory per list element plus n bytes/wordsize per integer element,
> where every integer element contain n characters.
> If the string length is not divisible by n, space is wasted (the string gets
> padded with zeros).
> Pick your the integer representation length.
> packstring/1 takes a string returns a list of n byte integers
> unpackstring/1 takes an integer representation and returns a string.
> There is a simple test suite in test/0.
> If anyone can improve upon this code, please do. If this was an exercise in
> futility, please let my know, I've only been programming erlang for 2 weeks
> and still need to learn all the gotchas ;)
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