From 6b32cae2605bdd091b49b7b69321ee024814ff4d Mon Sep 17 00:00:00 2001
From: Paul Eggert <eggert@cs.ucla.edu>
Date: Sat, 30 Jul 2022 08:55:51 -0700
Subject: [PATCH 1/3] Simplify subsecond precision handling

* ziguard.awk (get_rounding_subst):
Remove support for two-operand #STDOFF, as one-operand
suffices if the transition times are in UT.
All uses changed.
---
 asia         |  4 ++--
 northamerica |  4 ++--
 ziguard.awk  | 28 +++++++---------------------
 3 files changed, 11 insertions(+), 25 deletions(-)

diff --git a/asia b/asia
index a35d46dd..f481f399 100644
--- a/asia
+++ b/asia
@@ -857,8 +857,8 @@ Rule	HK	1973	only	-	Dec	30	3:30	1:00	S
 Rule	HK	1979	only	-	May	13	3:30	1:00	S
 Rule	HK	1979	only	-	Oct	21	3:30	0	-
 # Zone	NAME		STDOFF	RULES	FORMAT	[UNTIL]
-		#STDOFF	7:36:41.7			     0:36:41.7
-Zone	Asia/Hong_Kong	7:36:42 -	LMT	1904 Oct 30  0:36:42
+		#STDOFF	7:36:41.7
+Zone	Asia/Hong_Kong	7:36:42 -	LMT	1904 Oct 29 17:00u
 			8:00	-	HKT	1941 Jun 15  3:00
 			8:00	1:00	HKST	1941 Oct  1  4:00
 			8:00	0:30	HKWT	1941 Dec 25
diff --git a/northamerica b/northamerica
index a8858698..94f6ea38 100644
--- a/northamerica
+++ b/northamerica
@@ -353,8 +353,8 @@ Rule	NYC	1921	1966	-	Apr	lastSun	2:00	1:00	D
 Rule	NYC	1921	1954	-	Sep	lastSun	2:00	0	S
 Rule	NYC	1955	1966	-	Oct	lastSun	2:00	0	S
 # Zone	NAME		STDOFF	RULES	FORMAT	[UNTIL]
-		#STDOFF	-4:56:01.6			    12:03:58.4
-Zone America/New_York	-4:56:02 -	LMT	1883 Nov 18 12:03:58
+		#STDOFF	-4:56:01.6
+Zone America/New_York	-4:56:02 -	LMT	1883 Nov 18 17:00u
 			-5:00	US	E%sT	1920
 			-5:00	NYC	E%sT	1942
 			-5:00	US	E%sT	1946
diff --git a/ziguard.awk b/ziguard.awk
index c39e0d65..2f11f827 100644
--- a/ziguard.awk
+++ b/ziguard.awk
@@ -68,17 +68,6 @@ function round_to_second(timestamp, \
 		 seconds / 3600, seconds / 60 % 60, seconds % 60)
 }
 
-function get_rounding_subst(time, subst)
-{
-  if (DATAFORM == "vanguard") {
-    subst[0] = round_to_second(time)
-    subst[1] = time
-  } else {
-    subst[0] = time
-    subst[1] = round_to_second(time)
-  }
-}
-
 BEGIN {
   dataform_type["vanguard"] = 1
   dataform_type["main"] = 1
@@ -86,9 +75,6 @@ BEGIN {
 
   # The command line should set DATAFORM.
   if (!dataform_type[DATAFORM]) exit 1
-
-  stdoff_subst[0] = 0
-  until_subst[0] = 0
 }
 
 /^Zone/ { zone = $2 }
@@ -208,20 +194,20 @@ DATAFORM != "main" {
 
   # Prefer subseconds in vanguard form, whole seconds otherwise.
   if ($1 == "#STDOFF") {
-    get_rounding_subst($2, stdoff_subst)
-    if ($3) {
-      get_rounding_subst($3, until_subst)
+    stdoff = $2
+    rounded_stdoff = round_to_second(stdoff)
+    if (DATAFORM == "vanguard") {
+      stdoff_subst[0] = rounded_stdoff
+      stdoff_subst[1] = stdoff
     } else {
-      until_subst[0] = 0
+      stdoff_subst[0] = stdoff
+      stdoff_subst[1] = rounded_stdoff
     }
   } else if (stdoff_subst[0]) {
     stdoff_column = 2 * /^Zone/ + 1
     stdoff_column_val = $stdoff_column
     if (stdoff_column_val == stdoff_subst[0]) {
       sub(stdoff_subst[0], stdoff_subst[1])
-      if (until_subst[0] && $NF == until_subst[0]) {
-	sub(until_subst[0], until_subst[1])
-      }
     } else if (stdoff_column_val != stdoff_subst[1]) {
       stdoff_subst[0] = 0
     }
-- 
2.34.1