Merge pull request #4599 from urbit/jo/zuse-time-unfix

zuse: fix time fix regression

pkg/arvo/sys/zuse.hoon

@@ -5535,7 +5535,8 @@
     ::                                                  ::  ++unm:chrono:userlib
     ++  unm                                             ::  Urbit to Unix ms
       |=  a=@da
-      (div (mul (sub a ~1970.1.1) 1.000) ~s1)
+      =-  (div (mul - 1.000) ~s1)
+      (sub (add a (div ~s1 2.000)) ~1970.1.1)
     ::                                                  ::  ++unt:chrono:userlib
     ++  unt                                             ::  Urbit to Unix time
       |=  a=@da

pkg/arvo/tests/sys/zuse/format.hoon

@@ -179,6 +179,11 @@
     %+  expect-eq
       !>  [%n '1000']
       !>  (time ~1970.1.1..0.0.1)
+    ::  timestamps should invert
+    ::
+    %+  expect-eq
+      !>  [%n '1001']
+      !>  (time (from-unix-ms:chrono:userlib 1.001))
     :: ship - store ship identity as a string
     ::
     %+  expect-eq