1 files changed, 21 insertions, 0 deletions
diff --git a/src/libs6dns/s6dns_domain_arpafromip6.c b/src/libs6dns/s6dns_domain_arpafromip6.c
new file mode 100644
index 0000000..3b58127
--- /dev/null
+++ b/src/libs6dns/s6dns_domain_arpafromip6.c
@@ -0,0 +1,21 @@
+/* ISC license. */
+
+#include <skalibs/bytestr.h>
+#include <skalibs/fmtscan.h>
+#include <s6-dns/s6dns-domain.h>
+
+void s6dns_domain_arpafromip6 (s6dns_domain_t *d, char const *ip6, unsigned int mask)
+{
+  register unsigned int i ;
+  if (mask > 128) mask = 128 ;
+  mask = mask ? 1 + ((mask-1) >> 2) : 0 ;
+  d->len = 0 ;
+  d->s[d->len++] = '.' ;
+  for (i = 32 - mask ; i < 32 ; i++)
+  {
+    unsigned char c = ip6[15-(i>>1)] ;
+    d->s[d->len++] = fmtscan_asc((i & 1) ? (c >> 4) : (c & 15)) ;
+    d->s[d->len++] = '.' ;
+  }
+  byte_copy(d->s + d->len, 9, "ip6.arpa.") ; d->len += 9 ;
+}