1 files changed, 23 insertions, 0 deletions
diff --git a/src/libstddjb/ntp_from_tain.c b/src/libstddjb/ntp_from_tain.c
new file mode 100644
index 0000000..43d5a42
--- /dev/null
+++ b/src/libstddjb/ntp_from_tain.c
@@ -0,0 +1,23 @@
+/* ISC license. */
+
+#include <errno.h>
+#include <skalibs/uint64.h>
+#include <skalibs/tai.h>
+#include <skalibs/djbtime.h>
+
+int ntp_from_tain (uint64 *u, tain_t const *a)
+{
+  uint64 secs, frac ;
+  if (!utc_from_tai(&secs, tain_secp(a))) return 0 ;
+  secs += NTP_OFFSET ;
+  if (secs < TAI_MAGIC + 2147483648UL) goto ifail ;
+  secs -= TAI_MAGIC ;
+  if (secs >= ((uint64)3 << 31)) goto ifail ;
+  secs &= (secs < ((uint64)1 << 32)) ? 0xFFFFFFFFUL : 0x7FFFFFFFUL ;
+  frac = ((uint64)a->nano << 32) / 1000000000UL ;
+  *u = (secs << 32) + frac ;
+  return 1 ;
+ ifail:
+  errno = EINVAL ;
+  return 0 ;
+}