[Zlib-devel] [PING] Improve longest_match performance

[Andreas Krebbel]

On 24/07/12 16:56, John Reiser wrote:
> On 07/24/2012, Andreas Krebbel wrote:
> 
>> any comments regarding this one?
>>
>> http://mail.madler.net/pipermail/zlib-devel_madler.net/2012-June/002907.html
> 
> These changes in the width of variables which contribute to indexing
> of arrays:
> -----
> +    uLong cur_match = pcur_match; /* extend to pointer width */
> 
> +    uLong wmask = s->w_mask;
> -----
> should use 'ptrdiff_t' instead. 

Right. I've verified that the same code is generated as before. Also it does not seem to
be necessary to promote wmask. So here is an updated version:

What do you think?

Bye,

-Andreas-

---
 deflate.c |   15 ++++++++-------
 1 file changed, 8 insertions(+), 7 deletions(-)

Index: zlib/deflate.c
===================================================================
--- zlib.orig/deflate.c
+++ zlib/deflate.c
@@ -1143,15 +1143,16 @@ local void lm_init (s)
 /* For 80x86 and 680x0, an optimized version will be provided in match.asm or
  * match.S. The code will be functionally equivalent.
  */
-local uInt longest_match(s, cur_match)
+local uInt longest_match(s, pcur_match)
     deflate_state *s;
-    IPos cur_match;                             /* current match */
+    IPos pcur_match;                             /* current match */
 {
+    ptrdiff_t cur_match = pcur_match; /* extend to pointer width */
     unsigned chain_length = s->max_chain_length;/* max hash chain length */
     register Bytef *scan = s->window + s->strstart; /* current string */
     register Bytef *match;                       /* matched string */
     register int len;                           /* length of current match */
-    int best_len = s->prev_length;              /* best match length so far */
+    ptrdiff_t best_len = s->prev_length;              /* best match length so far */
     int nice_match = s->nice_match;             /* stop if match long enough */
     IPos limit = s->strstart > (IPos)MAX_DIST(s) ?
         s->strstart - (IPos)MAX_DIST(s) : NIL;
@@ -1166,12 +1167,12 @@ local uInt longest_match(s, cur_match)
      * Try with and without -DUNALIGNED_OK to check.
      */
     register Bytef *strend = s->window + s->strstart + MAX_MATCH - 1;
-    register ush scan_start = *(ushf*)scan;
-    register ush scan_end   = *(ushf*)(scan+best_len-1);
+    register uInt scan_start = *(ushf*)scan;
+    register uInt scan_end   = *(ushf*)(scan+best_len-1);
 #else
     register Bytef *strend = s->window + s->strstart + MAX_MATCH;
-    register Byte scan_end1  = scan[best_len-1];
-    register Byte scan_end   = scan[best_len];
+    register uInt scan_end1  = scan[best_len-1];
+    register uInt scan_end   = scan[best_len];
 #endif

     /* The code is optimized for HASH_BITS >= 8 and MAX_MATCH-2 multiple of 16.