[Buildroot] [PATCH] pkg-utils: describe the case conversion macros in more detail.

[Yann E. MORIN]

Arnout, All,

On 2014-10-14 11:23 +0200, Arnout Vandecappelle (Essensium/Mind) spake thusly:
> 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 at mind.be>
> Cc: Thomas De Schampheleire <patrickdepinguin at gmail.com>

Reviewed-by: "Yann E. MORIN" <yann.morin.1998 at free.fr>

Regards,
Yann E. MORIN.

> ---
> Very old patch that I forgot to push
> 
> Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout at mind.be>
> ---
>  package/pkg-utils.mk | 26 ++++++++++++++++++--------
>  1 file changed, 18 insertions(+), 8 deletions(-)
> 
> diff --git a/package/pkg-utils.mk b/package/pkg-utils.mk
> index ce39197..7eddc47 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 _ _
>  
> -- 
> 2.1.1
> 
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> buildroot at busybox.net
> http://lists.busybox.net/mailman/listinfo/buildroot

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