Canonicalize CIDR: Difference between revisions

=={{header|C}}==

This solution uses only the standard library. On POSIX platforms one can use the functions

inet_pton/inet_ntop to parse/format IPv4 addresses.

<lang c>#include <stdbool.h>

#include <stdio.h>

#include <stdint.h>

typedef struct cidr_tag {

uint32_t address;

uint32_t mask;

} cidr_t;

// Convert a string in CIDR format to an IPv4 address and netmask,

// if possible. Also performs CIDR canonicalization.

bool cidr_parse(const char* str, cidr_t* cidr) {

int a, b, c, d, m;

if (sscanf(str, "%d.%d.%d.%d/%d", &a, &b, &c, &d, &m) != 5)

return false;

if (m < 1 || m > 32)

return false;

if (a < 0 || a > UINT8_MAX)

return false;

if (b < 0 || b > UINT8_MAX)

return false;

if (c < 0 || c > UINT8_MAX)

return false;

if (d < 0 || d > UINT8_MAX)

return false;

uint32_t mask = ~((1 << (32 - m)) - 1);

uint32_t address = (a << 24) + (b << 16) + (c << 8) + d;

address &= mask;

cidr->address = address;

cidr->mask = mask;

return true;

}

uint8_t mask_length(uint32_t mask) {

uint8_t length = 32;

for (; (mask & 1) == 0 && length > 0; mask >>= 1, --length) {}

return length;

}

// Write a string in CIDR notation into the supplied buffer.

void cidr_format(const cidr_t* cidr, char* str, size_t size) {

uint8_t m = mask_length(cidr->mask);

uint32_t address = cidr->address;

uint8_t d = address & UINT8_MAX;

address >>= 8;

uint8_t c = address & UINT8_MAX;

address >>= 8;

uint8_t b = address & UINT8_MAX;

address >>= 8;

uint8_t a = address & UINT8_MAX;

snprintf(str, size, "%hhu.%hhu.%hhu.%hhu/%hhu", a, b, c, d, m);

}

int main(int argc, char** argv) {

for (int i = 1; i < argc; ++i) {

cidr_t cidr;

if (cidr_parse(argv[i], &cidr)) {

char out[32];

cidr_format(&cidr, out, sizeof(out));

puts(out);

} else {

fprintf(stderr, "%s: invalid CIDR\n", argv[i]);

}

}

return 0;

}</lang>

{{out}}

<pre>

$ ./canonicalize_cidr 87.70.141.1/22

87.70.140.0/22

</pre>