Data commit

Task/Canonicalize-CIDR/C/canonicalize-cidr.c

@@ -0,0 +1,64 @@
+#include <stdbool.h>
+#include <stdio.h>
+#include <stdint.h>
+
+typedef struct cidr_tag {
+    uint32_t address;
+    unsigned int mask_length;
+} 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
+        || a < 0 || a > UINT8_MAX
+        || b < 0 || b > UINT8_MAX
+        || c < 0 || c > UINT8_MAX
+        || 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_length = m;
+    return true;
+}
+
+// Write a string in CIDR notation into the supplied buffer.
+void cidr_format(const cidr_t* cidr, char* str, size_t size) {
+    uint32_t address = cidr->address;
+    unsigned int d = address & UINT8_MAX;
+    address >>= 8;
+    unsigned int c = address & UINT8_MAX;
+    address >>= 8;
+    unsigned int b = address & UINT8_MAX;
+    address >>= 8;
+    unsigned int a = address & UINT8_MAX;
+    snprintf(str, size, "%u.%u.%u.%u/%u", a, b, c, d,
+             cidr->mask_length);
+}
+
+int main(int argc, char** argv) {
+    const char* tests[] = {
+        "87.70.141.1/22",
+        "36.18.154.103/12",
+        "62.62.197.11/29",
+        "67.137.119.181/4",
+        "161.214.74.21/24",
+        "184.232.176.184/18"
+    };
+    for (int i = 0; i < sizeof(tests)/sizeof(tests[0]); ++i) {
+        cidr_t cidr;
+        if (cidr_parse(tests[i], &cidr)) {
+            char out[32];
+            cidr_format(&cidr, out, sizeof(out));
+            printf("%-18s -> %s\n", tests[i], out);
+        } else {
+            fprintf(stderr, "%s: invalid CIDR\n", tests[i]);
+        }
+    }
+    return 0;
+}