+GZIP="$(which gzip)"
+
+# try to use fixed source epoch
+if [ -n "$SOURCE_DATE_EPOCH" ]; then
+ TIMESTAMP=$(date --date="@$SOURCE_DATE_EPOCH")
+
+# look up date of last commit
+elif [ -d "$TOPDIR/.git" ]; then
+ GIT="$(which git)"
+ TIMESTAMP=$(cd $TOPDIR; $GIT log -1 -s --format=%ci)
+elif [ -d "$TOPDIR/.svn" ]; then
+ SVN="$(which svn)"
+ TIMESTAMP=$($SVN info "$TOPDIR" | sed -n "s/^Last Changed Date: \(.*\)/\1/p")
+else
+ TIMESTAMP=$(date)
+fi