From 9a89b98ae2a0af31dbad881fd47d29b1fe15d11f Mon Sep 17 00:00:00 2001 From: Arnout Vandecappelle Date: Tue, 14 Oct 2014 11:23:47 +0200 Subject: [PATCH] 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) Cc: Thomas De Schampheleire Reviewed-by: "Yann E. MORIN" Signed-off-by: Thomas Petazzoni --- package/pkg-utils.mk | 24 +++++++++++++++++------- 1 file changed, 17 insertions(+), 7 deletions(-) diff --git a/package/pkg-utils.mk b/package/pkg-utils.mk index ce39197f2e..7eddc47a09 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 +# 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. -# 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) [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 _ _