Add function to compare prefixes, with an enumeration.

util.c

@@ -28,6 +28,7 @@ THE SOFTWARE.
 #include <stdio.h>
 #include <unistd.h>
 #include <limits.h>
+#include <assert.h>
 
 #include <sys/types.h>
 #include <sys/socket.h>
@@ -488,3 +489,30 @@ daemonise()
 
     return 1;
 }
+
+enum prefix_status
+prefix_cmp(const unsigned char *p1, unsigned char plen1,
+           const unsigned char *p2, unsigned char plen2)
+{
+    int min = MIN(plen1, plen2);
+    unsigned char mask = 0xFF;
+    int i = 0;
+
+    while(i < min / 8) {
+        if(p1[i] != p2[i])
+            return PST_DISJOINT;
+        i++;
+    }
+    min -= i * 8;
+    if(min != 0) {
+        mask <<= 8 - min;
+        if((p1[i] & mask) != (p2[i] & mask))
+            return PST_DISJOINT;
+    }
+
+    if(plen1 < plen2)
+        return PST_LESS_SPECIFIC;
+    if(plen1 > plen2)
+        return PST_MORE_SPECIFIC;
+    return PST_EQUALS;
+}

util.h

@@ -112,6 +112,16 @@ int v4mapped(const unsigned char *address) ATTRIBUTE ((pure));
 void v4tov6(unsigned char *dst, const unsigned char *src);
 int daemonise(void);
 
+enum prefix_status {
+    PST_DISJOINT      = 1 << 0,
+    PST_EQUALS        = 1 << 1,
+    PST_MORE_SPECIFIC = 1 << 2,
+    PST_LESS_SPECIFIC = 1 << 3,
+};
+enum prefix_status
+prefix_cmp(const unsigned char *p1, unsigned char plen1,
+           const unsigned char *p2, unsigned char plen2);
+
 /* If debugging is disabled, we want to avoid calling format_address
    for every omitted debugging message.  So debug is a macro.  But
    vararg macros are not portable. */