From cace650c47db6c7598bdc1b3a69e853538db600e Mon Sep 17 00:00:00 2001
From: Holger Vogt <holger.vogt@uni-due.de>
Date: Sat, 4 Aug 2018 23:38:03 +0200
Subject: [PATCH] timestamp may be overruled by setting env var
 SOURCE_DATE_EPOCH to allow Reproducible builds See
 https://wiki.debian.org/ReproducibleBuilds

---
 configure.ac | 20 +++++++++++++++++++-
 1 file changed, 19 insertions(+), 1 deletion(-)

diff --git a/configure.ac b/configure.ac
index 824e35a67..4f62b7a4b 100644
--- a/configure.ac
+++ b/configure.ac
@@ -809,7 +809,25 @@ else
 AC_DEFINE_UNQUOTED([NGSPICEBINDIR], ["`echo $dprefix/bin`"], [Define the directory for executables])
 AC_DEFINE_UNQUOTED([NGSPICEDATADIR], ["`echo $dprefix/share/ngspice`"], [Define the directory for architecture independent data files])
 fi
-AC_DEFINE_UNQUOTED([NGSPICEBUILDDATE], ["`date`"], [Define the build date])
+
+# Create timestamp, may be overruled by setting env var SOURCE_DATE_EPOCH
+case $host_os in
+    *freebsd* )
+        DATE_FMT="%Y-%m-%d"
+        SOURCE_DATE_EPOCH="${SOURCE_DATE_EPOCH:-$(date +%s)}"
+        BUILD_DATE=$(date -u -d "@$SOURCE_DATE_EPOCH" "+$DATE_FMT" 2>/dev/null || date -u -r "$SOURCE_DATE_EPOCH" "+$DATE_FMT" 2>/dev/null || date -u "+$DATE_FMT")
+        ;;
+    *openbsd* )
+        DATE_FMT="%Y-%m-%d"
+        SOURCE_DATE_EPOCH="${SOURCE_DATE_EPOCH:-$(date +%s)}"
+        BUILD_DATE=$(date -u -d "@$SOURCE_DATE_EPOCH" "+$DATE_FMT" 2>/dev/null || date -u -r "$SOURCE_DATE_EPOCH" "+$DATE_FMT" 2>/dev/null || date -u "+$DATE_FMT")
+        ;;
+    * )
+        BUILD_DATE="$(date --utc --date="@${SOURCE_DATE_EPOCH:-$(date +%s)}")"
+        ;;
+esac
+
+AC_DEFINE_UNQUOTED([NGSPICEBUILDDATE], ["$BUILD_DATE"], [Define the build date])
 
 if test "x$with_wingui" = xyes; then
     AC_MSG_RESULT([WINDOWS GUI code enabled])