/* * cidr.c - functions to process addresses in CIDR notation * * Copyright (c) Gerard Paul Java 2003 * * This module contains functions that deal with CIDR address/mask notation. * * This module may be freely used for any purpose, commercial or otherwise, * In any product that uses this module, the following notice must appear: * *     Includes software developed by Gerard Paul Java *     Copyright (c) Gerard Paul Java 2003 */#include <stdlib.h>#include <sys/socket.h>#include <netinet/in.h>#include <arpa/inet.h>#include <string.h>/* * Returns a binary subnet mask based on the number of mask bits.  The * dotted-decimal notation may be obtained with inet_ntoa. */unsigned long cidr_get_mask(unsigned int maskbits){    struct in_addr mask;    if (maskbits == 0)        return 0;    inet_aton("255.255.255.255", &mask);    mask.s_addr = htonl(mask.s_addr << (32 - maskbits));    return mask.s_addr;}/* * Returns a subnet mask in dotted-decimal notation given the number of * 1-bits in the mask. */char *cidr_get_quad_mask(unsigned int maskbits){    struct in_addr addr;    addr.s_addr = cidr_get_mask(maskbits);    return inet_ntoa(addr);}/* * Returns the number of 1-bits in the given binary subnet mask in * network byte order. */unsigned int cidr_get_maskbits(unsigned long mask){    unsigned int i = 32;    if (mask == 0)        return 0;    mask = ntohl(mask);    while (mask % 2 == 0) {        mask >>= 1;        i--;    }    return i;}/* * Splits a CIDR-style address/mask string into its constituent address and * mask parts.  In case of absent or invalid input in the mask part, 255 is * returned in *maskbits (255 is invalid for an IPv4 address). */void cidr_split_address(char *cidr_addr, char *addresspart,                        unsigned int *maskbits){    char maskpart[4];    char *endptr;    char *slashptr;    char address_buffer[80];    if (strchr(cidr_addr, '/') == NULL) {        strncpy(addresspart, cidr_addr, 80);        *maskbits = 255;        return;    }    memset(address_buffer, 0, 80);    memset(addresspart, 0, 80);    memset(maskpart, 0, 4);    strncpy(address_buffer, cidr_addr, 80);    slashptr = strchr(address_buffer, '/');    /*     * Cut out the mask part and move past the slash     */    *slashptr = '\0';    slashptr++;    /*     * Copy out the address and mask parts into their buffers.     */    strncpy(addresspart, address_buffer, 80);    strncpy(maskpart, slashptr, 4);    if (maskpart[0] != '\0') {        *maskbits = strtoul(maskpart, &endptr, 10);        if (*endptr != '\0')            *maskbits = 255;    } else        *maskbits = 255;    return;}