[Mesa-dev] [PATCH v2 3/3] util: use faster zlib's CRC32 implementaion

[Grazvydas Ignotas]

zlib provides a faster slice-by-4 CRC32 implementation than the
traditional single byte lookup one used by mesa. As most supported
platforms now link zlib unconditionally, we can easily use it.

Improvement for a 1MB buffer (avg MB/s, n=100, zlib 1.2.8):

  i5-6600K                    C2D E4500
mesa zlib                    mesa zlib
 443 1443 225% +/- 2.1%       403 1175 191% +/- 0.9%

It has been verified the calculation results stay the same after this
change.

Signed-off-by: Grazvydas Ignotas <notasas at gmail.com>
---
v2: drop the size threshold check because size is unlikely to be that
low of things mesa is typically hashing

 src/util/crc32.c | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/src/util/crc32.c b/src/util/crc32.c
index f2e01c6..9edd3e1 100644
--- a/src/util/crc32.c
+++ b/src/util/crc32.c
@@ -31,10 +31,13 @@
  * 
  * @author Jose Fonseca
  */
 
 
+#ifdef HAVE_ZLIB
+#include <zlib.h>
+#endif
 #include "crc32.h"
 
 
 static const uint32_t 
 util_crc32_table[256] = {
@@ -112,10 +115,19 @@ uint32_t
 util_hash_crc32(const void *data, size_t size)
 {
    const uint8_t *p = data;
    uint32_t crc = 0xffffffff;
  
+#ifdef HAVE_ZLIB
+   /* zlib's uInt is always "unsigned int" while size_t can be 64bit.
+    * Since 1.2.9 there's crc32_z that takes size_t, but use the more
+    * available function to avoid build system complications.
+    */
+   if ((uInt)size == size)
+      return ~crc32(0, data, size);
+#endif
+
    while (size--)
       crc = util_crc32_table[(crc ^ *p++) & 0xff] ^ (crc >> 8);
    
    return crc;
 }
-- 
2.7.4