Generic dynamic resize routine

dynarray_ensure_size.c

void dynarray_ensure_size(size_t num,size_t* pcap,void** buf,size_t szof)
{
    void* newbuf;
    size_t newsz;
    size_t cap = *pcap;

    if (cap == 0) {
        if (16 > num) {
            *pcap = cap = 16;
        }
        else {
            size_t rem = num % 8;
            *pcap = cap = (num + (rem ? 8-rem : 0));
        }
        newsz = cap * szof;
        *buf = newbuf = srp_malloc(newsz);
        memset(newbuf,0,newsz);
    }
    else if (num >= cap) {
        size_t oldsz;
        void* oldbuf;
        size_t newcap = cap;

        do {
            newcap *= 2;
        } while (newcap < num);

        newsz = newcap * szof;
        oldsz = szof * cap;
        newbuf = srp_malloc(newsz);
        oldbuf = *buf;

        memcpy(newbuf,oldbuf,oldsz);
        memset((char*)newbuf + oldsz,0,newsz - oldsz);

        free(oldbuf);
        *buf = newbuf;
        *pcap = newcap;
    }
}