diff options
| author | Arnout Vandecappelle <arnout@mind.be> | 2014-10-14 11:23:47 +0200 |
|---|---|---|
| committer | Thomas Petazzoni <thomas.petazzoni@free-electrons.com> | 2014-10-16 19:04:18 +0200 |
| commit | 9a89b98ae2a0af31dbad881fd47d29b1fe15d11f (patch) | |
| tree | 878a0b074d3361cecc0461a10743ac6d2384ea6d /package/pkg-utils.mk | |
| parent | 307df2883ed6f0ca583f8d6c9b87a9789d122507 (diff) | |
pkg-utils: describe the case conversion macros in more detail.
After the refactoring of the case conversion macros in dd5e620ac, the
macro became even harder to understand. Improve this explanation a
little so future generations can make sense of what we're doing here.
Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>
Cc: Thomas De Schampheleire <patrickdepinguin@gmail.com>
Reviewed-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Diffstat (limited to 'package/pkg-utils.mk')
| -rw-r--r-- | package/pkg-utils.mk | 26 |
1 files changed, 18 insertions, 8 deletions
diff --git a/package/pkg-utils.mk b/package/pkg-utils.mk index ce39197f2..7eddc47a0 100644 --- a/package/pkg-utils.mk +++ b/package/pkg-utils.mk @@ -5,14 +5,24 @@ # ################################################################################ -# UPPERCASE Macro -- transform its argument to uppercase and replace dots and -# hyphens to underscores - -# Heavily inspired by the up macro from gmsl (http://gmsl.sf.net) -# This is approx 5 times faster than forking a shell and tr, and -# as this macro is used a lot it matters -# This works by creating translation character pairs (E.G. a:A b:B) -# and then looping though all of them running $(subst from,to,text) +# Case conversion macros. This is inspired by the 'up' macro from gmsl +# (http://gmsl.sf.net). It is optimised very heavily because these macros +# are used a lot. It is about 5 times faster than forking a shell and tr. +# +# The caseconvert-helper creates a definition of the case conversion macro. +# After expansion by the outer $(eval ), the UPPERCASE macro is defined as: +# $(strip $(eval __tmp := $(1)) $(eval __tmp := $(subst a,A,$(__tmp))) ... ) +# In other words, every letter is substituted one by one. +# +# The caseconvert-helper allows us to create this definition out of the +# [FROM] and [TO] lists, so we don't need to write down every substition +# manually. The uses of $ and $$ quoting are chosen in order to do as +# much expansion as possible up-front. +# +# Note that it would be possible to conceive a slightly more optimal +# implementation that avoids the use of __tmp, but that would be even +# more unreadable and is not worth the effort. + [FROM] := a b c d e f g h i j k l m n o p q r s t u v w x y z - . [TO] := A B C D E F G H I J K L M N O P Q R S T U V W X Y Z _ _ |