struct bitmap{    unsigned int len;    unsigned char* buf;};struct bitmap* creat_bitmap(unsigned int len){    struct bitmap *bm;        if (len <=0)        return(NULL);        if ((bm = malloc(sizeof(struct bitmap))) == NULL)        return(NULL);            if ((bm->buf = malloc(len)) == NULL)    {            free(bm);            return(NULL);    }    memset(bm->buf, 0, len);    bm->len = len;    return(bm);}void free_bitmap(struct bitmap* bm){    if (!bm)        return;    if (bm->buf)        free(bm->buf);    free(bm);}int set_bitmap_pos(struct bitmap* bm, unsigned int index, int value){    unsigned int    x = index / 8;    unsigned int    y = index % 8;    unsigned char    mask = 0x80;        if (index > bm->len)        return(-1);        if (y == 0)    {        if (x > 0)        {            --x;            y = 7;        }    }    if (value)        bm->buf[x] |= mask>>y;//把buf的第index bit置1    else        bm->buf[x] &= ~(mask>>y);//把buf的第index bit置0    return(1);}//检查bitmap的第 index bit 的值int check_bitmap(struct bitmap* bm, unsigned int index){    unsigned int    x = index / 8;    unsigned int    y = index % 8;    unsigned char    mask = 0x80;        if (index > bm->len)        return(-1);        if (y == 0)    {        if (x > 0)        {            --x;            y = 7;        }    }        return(bm->buf[x] & (mask>>y)?1:0);}