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

[Christophe JAILLET]

Le 22/09/2017 à 00:19, Colin King a écrit :
From: Colin Ian King <colin.k...@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.k...@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)));