Zlib implements a byte-by-byte and a word-by-word longest_match() string
comparision function. This implementation defaults to the slower byte-by-byte
version unless the preprocessor macro UNALIGNED_OK is defined.
Currently, nothing is hooked up to define this macro, but we do have
CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS, which serves the same purpose.
The exact performance improvement of the word-by-word implementation is data
dependant, but on x86 it is typically in the range of a 5-10% cycle reduction.
The code is already there, might as well use it ...
Signed-off-by: Jim Kukunas <james.t.kuku...@linux.intel.com>
---
lib/zlib_deflate/deflate.c | 15 ++++++++-------
1 files changed, 8 insertions(+), 7 deletions(-)
diff --git a/lib/zlib_deflate/deflate.c b/lib/zlib_deflate/deflate.c
index d20ef45..4920e51 100644
--- a/lib/zlib_deflate/deflate.c
+++ b/lib/zlib_deflate/deflate.c
@@ -570,9 +570,9 @@ static uInt longest_match(
Pos *prev = s->prev;
uInt wmask = s->w_mask;
-#ifdef UNALIGNED_OK
+#ifdef CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS
/* Compare two bytes at a time. Note: this is not always beneficial.
- * Try with and without -DUNALIGNED_OK to check.
+ * Try with and without -DCONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS to check.
*/
register Byte *strend = s->window + s->strstart + MAX_MATCH - 1;
register ush scan_start = *(ush*)scan;
@@ -606,9 +606,10 @@ static uInt longest_match(
/* Skip to next match if the match length cannot increase
* or if the match length is less than 2:
*/
-#if (defined(UNALIGNED_OK) && MAX_MATCH == 258)
+#if (defined(CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS) && MAX_MATCH == 258)
/* This code assumes sizeof(unsigned short) == 2. Do not use
- * UNALIGNED_OK if your compiler uses a different size.
+ * CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS if your compiler uses a
+ * different size.
*/
if (*(ush*)(match+best_len-1) != scan_end ||
*(ush*)match != scan_start) continue;
@@ -639,7 +640,7 @@ static uInt longest_match(
len = (MAX_MATCH - 1) - (int)(strend-scan);
scan = strend - (MAX_MATCH-1);
-#else /* UNALIGNED_OK */
+#else /* CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS */
if (match[best_len] != scan_end ||
match[best_len-1] != scan_end1 ||
@@ -670,13 +671,13 @@ static uInt longest_match(
len = MAX_MATCH - (int)(strend - scan);
scan = strend - MAX_MATCH;
-#endif /* UNALIGNED_OK */
+#endif /* CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS */
if (len > best_len) {
s->match_start = cur_match;
best_len = len;
if (len >= nice_match) break;
-#ifdef UNALIGNED_OK
+#ifdef CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS
scan_end = *(ush*)(scan+best_len-1);
#else
scan_end1 = scan[best_len-1];
--
1.7.1
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majord...@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
