unicode 转 utf8

int unicode_to_utf8(uint16 *in, int insize, unsigned char **out)
{
    int i = 0;
    int outsize = 0;
    int charscount = 0;
    unsigned char *result = NULL;
    unsigned char *tmp = NULL;

    charscount = insize;
    result = (unsigned char*)malloc(charscount * 3 + 1);
    memset(result, 0, charscount * 3 + 1);
    tmp = result;

    for (i = 0; i < charscount; i++)
    {
        uint16 unicode = in[i];

        if (unicode >= 0x0000 && unicode <= 0x007f)
        {
            *tmp = (char)unicode;
            tmp += 1;
            outsize += 1;
        }
        else if (unicode >= 0x0080 && unicode <= 0x07ff)
        {
            *tmp = 0xc0 | (unicode >> 6);
            tmp += 1;
            *tmp = 0x80 | (unicode & (0xff >> 2));
            tmp += 1;
            outsize += 2;
        }
        else if (unicode >= 0x0800 && unicode <= 0xffff)
        {
            *tmp = 0xe0 | (unicode >> 12);
            tmp += 1;
            *tmp = 0x80 | (unicode >> 6 & 0x003f);
            tmp += 1;
            *tmp = 0x80 | (unicode & (0xff >> 2));
            tmp += 1;
            outsize += 3;
        }

    }

    *tmp = '\0';
    *out = result;
    return 0;
}