lua utf-8

原文网址：https://github.com/alexander-yakushev/awesomerc/blob/master/awesompd/utf8.lua

-- Provides UTF-8 aware string functions implemented in pure lua:

-- * string.utf8len(s)

-- * string.utf8sub(s, i, j)

--

-- All functions behave as their non UTF-8 aware counterparts with the exception

-- that UTF-8 characters are used instead of bytes for all units.

--

-- Note: all validations had been removed due to awesome usage specifics.

--[[

Copyright (c) 2006-2007, Kyle Smith

Modified by Alexander Yakushev, 2010-2013.

All rights reserved.

Redistribution and use in source and binary forms, with or without

modification, are permitted provided that the following conditions are met:

* Redistributions of source code must retain the above copyright notice,

this list of conditions and the following disclaimer.

* Redistributions in binary form must reproduce the above copyright

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documentation and/or other materials provided with the distribution.

* Neither the name of the author nor the names of its contributors may be

used to endorse or promote products derived from this software without

specific prior written permission.

THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"

AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE

IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE

DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE

FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL

DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR

SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER

CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,

OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE

OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

--]]

-- ABNF from RFC 3629

--

-- UTF8-octets = *( UTF8-char )

-- UTF8-char = UTF8-1 / UTF8-2 / UTF8-3 / UTF8-4

-- UTF8-1 = %x00-7F

-- UTF8-2 = %xC2-DF UTF8-tail

-- UTF8-3 = %xE0 %xA0-BF UTF8-tail / %xE1-EC 2( UTF8-tail ) /

-- %xED %x80-9F UTF8-tail / %xEE-EF 2( UTF8-tail )

-- UTF8-4 = %xF0 %x90-BF 2( UTF8-tail ) / %xF1-F3 3( UTF8-tail ) /

-- %xF4 %x80-8F 2( UTF8-tail )

-- UTF8-tail = %x80-BF

--

-- returns the number of bytes used by the UTF-8 character at byte i in s

-- also doubles as a UTF-8 character validator

local utf8= {}

function utf8.charbytes (s, i)

-- argument defaults

i = i or 1

local c = string.byte(s, i)

-- determine bytes needed for character, based on RFC 3629

if c > 0 and c <= 127 then

-- UTF8-1

return 1

elseif c >= 194 and c <= 223 then

-- UTF8-2

local c2 = string.byte(s, i + 1)

return 2

elseif c >= 224 and c <= 239 then

-- UTF8-3

local c2 = s:byte(i + 1)

local c3 = s:byte(i + 2)

return 3

elseif c >= 240 and c <= 244 then

-- UTF8-4

local c2 = s:byte(i + 1)

local c3 = s:byte(i + 2)

local c4 = s:byte(i + 3)

return 4

end

end

-- returns the number of characters in a UTF-8 string

function utf8.len (s)

local pos = 1

local bytes= string.len(s)

local len = 0

while pos <= bytes and len ~= charsdo

local c = string.byte(s,pos)

len = len + 1

pos = pos + utf8.charbytes(s, pos)

end

if chars ~= nil then

return pos- 1

end

return len

end

-- functions identically to string.sub except that i and j are UTF-8 characters

-- instead of bytes

function utf8.sub (s, i, j)

j = j or -1

if i == nil then

return ""

end

local pos= 1

local bytes= string.len(s)

local len= 0

-- only set l if i or j is negative

local l = (i >= 0 and j >= 0) or utf8.len(s)

local startChar= (i >= 0)and i or l + i + 1

local endChar= (j >= 0)and j or l + j + 1

-- can't have start before end!

if startChar> endChar then

return ""

end

-- byte offsets to pass to string.sub

local startByte, endByte= 1, bytes

while pos<= bytes do

len = len+ 1

if len == startChar then

startByte = pos

end

pos = pos+ utf8.charbytes(s, pos)

if len == endChar then

endByte = pos- 1

break

end

end

return string.sub(s, startByte, endByte)

end

-- replace UTF-8 characters based on a mapping table

function utf8.replace (s, mapping)

local pos= 1

local bytes= string.len(s)

local charbytes

local newstr= ""

while pos<= bytes do

charbytes = utf8.charbytes(s, pos)

local c = string.sub(s, pos, pos + charbytes- 1)

newstr = newstr.. (mapping[c] or c)

pos = pos+ charbytes

end

return newstr

end

return utf8