Lua UTF-8 全角转半角

根据UTF-8的编码规则，可以知道：

1. 全角空格为12288，半角空格为32

2. 其他字符半角(33-126)与全角(65281-65374)的对应关系是：均相差65248

但是UTF-8不能字节转换位整型变量，因此需要一个函数，做一个转换：

function utf8_to_num(raw_string)
    local result = {}
    pos = 1
    while pos <= #raw_string do
        local count_1_of_byte = get_continuous_1_count_of_byte(string.byte(raw_string, pos))
        local num = 0

        if count_1_of_byte < 1 then 
            num = string.byte(raw_string, pos)
            count_1_of_byte = 1
        else 
            boundary = 8
            i = count_1_of_byte + 1
            while i < boundary * count_1_of_byte do
                if 0 == i % boundary then
                    i = i + 2
                end
                if (1 << (boundary - i % boundary - 1)) & string.byte(raw_string, pos + math.floor(i / boundary)) ~= 0 then
                    --print(1)
                    num = (num << 1) | 1
                else
                    --print(0)
                    num = num << 1
                end
                i= i + 1
            end
        end
        pos = pos + count_1_of_byte
        table.insert(result, num)
    end

    return result
end

为了方便将一个utf8字符，转换成整型，还需要判断一个utf8字符占了多少个字节，为此需要一个函数来判断（具体参考： http://blog.csdn.net/SKY453589103/article/details/76337557）：

--获取一个字节中，从最高位开始连续的1的个数
function  get_continuous_1_count_of_byte(num)
    if nil == num then 
        return -1
    end
    local count = 0
    while num & 0x80 ~= 0 do
        count = count + 1
        num = num << 1
    end
    return count
end

接下来就只转换的函数：

function full_width_to_half_width(raw_string)
    local new_string = {}
    local pos = 1
    while pos <= #raw_string do
        local count_1_of_byte = get_continuous_1_count_of_byte(string.byte(raw_string, pos))
        if 3 == count_1_of_byte then
            char = string.sub(raw_string, pos, pos + 2)
            num_of_char = utf8_to_num(char)[1]
            if 12288 == num_of_char then
                num_of_char = 32
                table.insert(new_string, string.char(num_of_char))
            elseif 65281 <= num_of_char and num_of_char <= 65374 then 
                num_of_char = num_of_char - 65248
                table.insert(new_string, string.char(num_of_char))
            end
            pos = pos + count_1_of_byte 
        else
            table.insert(new_string, string.sub(raw_string, pos, pos))
            pos = pos + 1
        end
    end

    return table.concat(new_string)
end

比较简单，就不做解释了。

Lua UTF-8 全角转半角

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