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##--
## Hacks for numeric comparisons.
# $(call version_ge,a,b)
# true iff a >= b when treated as vectors of integers separated by . or space
version_ge = $(strip $(call vge_2,$(subst ., ,$(1)),$(subst ., ,$(2))))
# if a is empty, result is true if b is empty otherwise false.
# if b is empty, result is true.
# if neither is empty, compare first words; if equal, strip one word and recurse.
define vge_2
$(if $(strip $(1)),
$(if $(strip $(2)),
$(if $(call numeric_lt,$(firstword $(2)),$(firstword $(1))),
t,
$(if $(call numeric_lt,$(firstword $(1)),$(firstword $(2))),
,
$(call vge_2,
$(wordlist 2,$(words $(1)),$(1)),
$(wordlist 2,$(words $(2)),$(2))))),
t),
$(if $(strip $(2)),,t))
endef
# $(call numeric_le,a,b) - true if a <= b, i.e. either a is 0 or a can index a [1..b] list
numeric_le = $(if $(filter 0,$(1)),t,$(word $(1),$(call nwords,$(2),)))
# $(call numeric_lt,a,b) - true if a < b, i.e. !(b <= a)
numeric_lt = $(if $(call numeric_le,$(2),$(1)),,t)
# list of N words
nwords = $(if $(filter-out 0,$(1)),$(if $(word $(1),$(2)),$(2),$(call nwords,$(1),$(2) t)))
## end of hacks.
##--
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