upstream_archive = $(OPK_SOURCE)-$(OPK_SOURCE_VERSION_UPSTREAM).tar.gz
source_version = $$(printf '%s\n' '$(OPK_SOURCE_VERSION)' | \
	sed 's/^\([0-9]*\.[0-9]\)\..*$$/\1/')
upstream_url = http://www.cmake.org/files/v$(source_version)/$(upstream_archive)
source_archive = ../$(OPK_SOURCE)-$(OPK_SOURCE_VERSION_UPSTREAM).orig.tar.gz

$(source_archive):
	wget -c $(upstream_url)
	printf '$(source_sha256sum)  $(upstream_archive)' | sha256sum -c -
	mv '$(upstream_archive)' '$@'

source: $(source_archive)