From 99e080c2f4dc243ef6f7d845e35295f62393cd52 Mon Sep 17 00:00:00 2001
From: Paul Eggert <eggert@cs.ucla.edu>
Date: Mon, 23 Dec 2019 23:48:35 -0800
Subject: [PATCH] nstrftime: tweak division performance
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* lib/nstrftime.c (SHR, tm_diff, __strftime_internal):
Redo with neither ‘%’ nor conditional branches.
---
 ChangeLog       |  4 ++++
 lib/nstrftime.c | 14 ++++++++------
 2 files changed, 12 insertions(+), 6 deletions(-)

diff --git a/ChangeLog b/ChangeLog
index 1f7eb19b9e..4b47142040 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,9 @@
 2019-12-23  Paul Eggert  <eggert@cs.ucla.edu>
 
+	nstrftime: tweak division performance
+	* lib/nstrftime.c (SHR, tm_diff, __strftime_internal):
+	Redo with neither ‘%’ nor conditional branches.
+
 	mktime: tweak division performance
 	* config/srclist.txt: Do not sync mktime.c for now.
 	* lib/mktime.c (shr, ydhms_diff):
diff --git a/lib/nstrftime.c b/lib/nstrftime.c
index 23b0a64608..62bc7a61e3 100644
--- a/lib/nstrftime.c
+++ b/lib/nstrftime.c
@@ -113,7 +113,7 @@ extern char *tzname[];
 #define SHR(a, b)       \
   (-1 >> 1 == -1        \
    ? (a) >> (b)         \
-   : (a) / (1 << (b)) - ((a) % (1 << (b)) < 0))
+   : ((a) + ((a) < 0)) / (1 << (b)) - ((a) < 0))
 
 #define TM_YEAR_BASE 1900
 
@@ -348,8 +348,8 @@ tm_diff (const struct tm *a, const struct tm *b)
      but it's OK to assume that A and B are close to each other.  */
   int a4 = SHR (a->tm_year, 2) + SHR (TM_YEAR_BASE, 2) - ! (a->tm_year & 3);
   int b4 = SHR (b->tm_year, 2) + SHR (TM_YEAR_BASE, 2) - ! (b->tm_year & 3);
-  int a100 = a4 / 25 - (a4 % 25 < 0);
-  int b100 = b4 / 25 - (b4 % 25 < 0);
+  int a100 = (a4 + (a4 < 0)) / 25 - (a4 < 0);
+  int b100 = (b4 + (b4 < 0)) / 25 - (b4 < 0);
   int a400 = SHR (a100, 2);
   int b400 = SHR (b100, 2);
   int intervening_leap_days = (a4 - b4) - (a100 - b100) + (a400 - b400);
@@ -927,9 +927,11 @@ __strftime_internal (STREAM_OR_CHAR_T *s, STRFTIME_ARG (size_t maxsize)
             }
 
           {
-            int century = tp->tm_year / 100 + TM_YEAR_BASE / 100;
-            century -= tp->tm_year % 100 < 0 && 0 < century;
-            DO_YEARISH (2, tp->tm_year < - TM_YEAR_BASE, century);
+            bool negative_year = tp->tm_year < - TM_YEAR_BASE;
+            bool zero_thru_1899 = !negative_year & (tp->tm_year < 0);
+            int century = ((tp->tm_year - 99 * zero_thru_1899) / 100
+                           + TM_YEAR_BASE / 100);
+            DO_YEARISH (2, negative_year, century);
           }
 
         case L_('x'):
-- 
2.39.5