Re: [PATCH] lib/lz4: make arrays static const, reduces object code size

Christophe JAILLET
2017-09-21T23:09:46Z

Le 22/09/2017 à 00:19, Colin King a écrit :
> From: Colin Ian King <colin.king@canonical.com>
>
> Don't populate the read-only arrays dec32table and dec64table on the
> stack, instead make them both static const. Makes the object code
> smaller by over 10K bytes:
10k? Wouaouh! This is way much more than what you usually win with such
patches.
I assume we must thanks FORCE_INLINE in this case.
Nice catch!

CJ

> Before:
> text data bss dec hex filename
> 31500 0 0 31500 7b0c lib/lz4/lz4_decompress.o
>
> After:
> text data bss dec hex filename
> 20237 176 0 20413 4fbd lib/lz4/lz4_decompress.o
>
> (gcc version 7.2.0 x86_64)
>
> Signed-off-by: Colin Ian King <colin.king@canonical.com>
> ---
> lib/lz4/lz4_decompress.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/lib/lz4/lz4_decompress.c b/lib/lz4/lz4_decompress.c
> index bd3574312b82..141734d255e4 100644
> --- a/lib/lz4/lz4_decompress.c
> +++ b/lib/lz4/lz4_decompress.c
> @@ -85,8 +85,8 @@ static FORCE_INLINE int LZ4_decompress_generic(
> const BYTE * const lowLimit = lowPrefix - dictSize;
>
> const BYTE * const dictEnd = (const BYTE *)dictStart + dictSize;
> - const unsigned int dec32table[] = { 0, 1, 2, 1, 4, 4, 4, 4 };
> - const int dec64table[] = { 0, 0, 0, -1, 0, 1, 2, 3 };
> + static const unsigned int dec32table[] = { 0, 1, 2, 1, 4, 4, 4, 4 };
> + static const int dec64table[] = { 0, 0, 0, -1, 0, 1, 2, 3 };
>
> const int safeDecode = (endOnInput = endOnInputSize);
> const int checkOffset = ((safeDecode) && (dictSize < (int)(64 * KB)));