--- /dev/null
+# Copyright © 2012, 2022 Nick Bowler
+#
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program. If not, see <https://www.gnu.org/licenses/>.
+
+AT_SETUP([upkg_decode_index])
+AT_KEYWORDS([core function])
+
+# various encodings of zero
+m4_foreach_w([INDEX], [00 4000 408000 40808000 4080808000],
+ [AT_CHECK([decodeindex INDEX], [0], [0
+])
+])
+
+# truncated encodings of zero
+m4_foreach_w([INDEX], ['' 40 4080 408080 40808080],
+ [AT_CHECK([decodeindex INDEX], [1], [ignore], [ignore])
+])
+
+# overlong encoding of zero
+AT_CHECK([decodeindex 408080808000], [1], [ignore], [ignore])
+
+AT_CLEANUP
+
+AT_SETUP([pcx_write_scanline run-length encoding])
+AT_KEYWORDS([engine function])
+
+AT_CHECK([pcxrle 00], [0], [00
+])
+AT_CHECK([pcxrle 0000], [0], [c200
+])
+AT_CHECK([pcxrle c100], [0], [c1c100
+])
+
+zero1=00
+zero4=$zero1$zero1$zero1$zero1
+zero16=$zero4$zero4$zero4$zero4
+zero63=$zero16$zero16$zero16$zero4$zero4$zero4$zero1$zero1$zero1
+zero64=$zero16$zero16$zero16$zero16
+zero192=$zero64$zero64$zero64
+
+AT_CHECK([# maximum possible run
+pcxrle $zero63], [0], [ff00
+])
+AT_CHECK([# one more than maximum
+pcxrle $zero64], [0], [ff0000
+])
+AT_CHECK([# consecutive runs
+pcxrle $zero192], [0], [ff00ff00ff00c300
+])
+
+AT_CLEANUP