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Subject[PATCH] crc32 improvements for 2.5
Hi

I did the optimizations in the crc32 patch Brian Murphy submitted a while ago.
Now I have cleaned it up a little and made some more optimizations.

gcc is quite bad at loop optimizations (at least for PPC) so I have
rewritten them to make gcc to generate better code. Even recent gcc's(3.2.x) produces
better code.

Also reduced the unrolling since it did not make a noticeable difference.

Joakim Tjernlund

--- lib/crc32.c.org Thu Jan 9 00:19:02 2003
+++ lib/crc32.c Tue Feb 4 19:05:01 2003
@@ -87,55 +87,51 @@
{
# if CRC_LE_BITS == 8
const u32 *b =(u32 *)p;
- const u32 *e;
- /* load data 32 bits wide, xor data 32 bits wide. */
+ const u32 *tab = crc32table_le;

- crc = __cpu_to_le32(crc);
- /* Align it */
- for ( ; ((long)b)&3 && len ; len--){
-# ifdef __LITTLE_ENDIAN
- crc = (crc>>8) ^ crc32table_le[ (crc ^ *((u8 *)b)++) & 0xff ];
-# else
- crc = (crc<<8) ^ crc32table_le[ crc>>24 ^ *((u8 *)b)++ ];
-# endif
- }
- e = (u32 *) ( (u8 *)b + (len & ~7));
- while (b < e) {
- crc ^= *b++;
-# ifdef __LITTLE_ENDIAN
- crc = (crc>>8) ^ crc32table_le[ crc & 0xff ];
- crc = (crc>>8) ^ crc32table_le[ crc & 0xff ];
- crc = (crc>>8) ^ crc32table_le[ crc & 0xff ];
- crc = (crc>>8) ^ crc32table_le[ crc & 0xff ];
-# else
- crc = (crc<<8) ^ crc32table_le[ crc >> 24 ];
- crc = (crc<<8) ^ crc32table_le[ crc >> 24 ];
- crc = (crc<<8) ^ crc32table_le[ crc >> 24 ];
- crc = (crc<<8) ^ crc32table_le[ crc >> 24 ];
-# endif
- crc ^= *b++;
# ifdef __LITTLE_ENDIAN
- crc = (crc>>8) ^ crc32table_le[ crc & 0xff ];
- crc = (crc>>8) ^ crc32table_le[ crc & 0xff ];
- crc = (crc>>8) ^ crc32table_le[ crc & 0xff ];
- crc = (crc>>8) ^ crc32table_le[ crc & 0xff ];
+# define DO_CRC crc = (crc>>8) ^ tab[ crc & 255 ]
+# define ENDIAN_SHIFT 0
# else
- crc = (crc<<8) ^ crc32table_le[ crc >> 24 ];
- crc = (crc<<8) ^ crc32table_le[ crc >> 24 ];
- crc = (crc<<8) ^ crc32table_le[ crc >> 24 ];
- crc = (crc<<8) ^ crc32table_le[ crc >> 24 ];
+# define DO_CRC crc = (crc<<8) ^ tab[ crc >> 24 ]
+# define ENDIAN_SHIFT 24
# endif
+
+ crc = __cpu_to_le32(crc);
+ /* Align it */
+ if(unlikely(((long)b)&3 && len)){
+ do {
+ crc ^= *((u8 *)b)++ << ENDIAN_SHIFT;
+ DO_CRC;
+ } while ((--len) && ((long)b)&3 );
+ }
+ if(likely(len >= 4)){
+ /* load data 32 bits wide, xor data 32 bits wide. */
+ size_t save_len = len & 3;
+ len = len >> 2;
+ --b; /* use pre increment below(*++b) for speed */
+ do {
+ crc ^= *++b;
+ DO_CRC;
+ DO_CRC;
+ DO_CRC;
+ DO_CRC;
+ } while (--len);
+ b++; /* point to next byte(s) */
+ len = save_len;
}
/* And the last few bytes */
- e = (u32 *)((u8 *)b + (len & 7));
- while (b < e){
-# ifdef __LITTLE_ENDIAN
- crc = (crc>>8) ^ crc32table_le[ (crc ^ *((u8 *)b)++) & 0xff ];
-# else
- crc = (crc<<8) ^ crc32table_le[ crc>>24 ^ *((u8 *)b)++ ];
-# endif
+ if(len){
+ do {
+ crc ^= *((u8 *)b)++ << ENDIAN_SHIFT;
+ DO_CRC;
+ } while (--len);
}
- return __le32_to_cpu(crc) ;
+
+ return __le32_to_cpu(crc);
+#undef ENDIAN_SHIFT
+#undef DO_CRC
+
# elif CRC_LE_BITS == 4
while (len--) {
crc ^= *p++;
@@ -196,55 +192,50 @@
{
# if CRC_BE_BITS == 8
const u32 *b =(u32 *)p;
- const u32 *e;
- /* load data 32 bits wide, xor data 32 bits wide. */
+ const u32 *tab = crc32table_be;

- crc = __cpu_to_be32(crc);
- /* Align it */
- for ( ; ((long)b)&3 && len ; len--){
-# ifdef __LITTLE_ENDIAN
- crc = (crc>>8) ^ crc32table_be[ (crc ^ *((u8 *)b)++) & 0xff ];
-# else
- crc = (crc<<8) ^ crc32table_be[ crc>>24 ^ *((u8 *)b)++ ];
-# endif
- }
- e = (u32 *) ( (u8 *)b + (len & ~7));
- while (b < e) {
- crc ^= *b++;
-# ifdef __LITTLE_ENDIAN
- crc = (crc>>8) ^ crc32table_be[ crc & 0xff ];
- crc = (crc>>8) ^ crc32table_be[ crc & 0xff ];
- crc = (crc>>8) ^ crc32table_be[ crc & 0xff ];
- crc = (crc>>8) ^ crc32table_be[ crc & 0xff ];
-# else
- crc = (crc<<8) ^ crc32table_be[ crc >> 24 ];
- crc = (crc<<8) ^ crc32table_be[ crc >> 24 ];
- crc = (crc<<8) ^ crc32table_be[ crc >> 24 ];
- crc = (crc<<8) ^ crc32table_be[ crc >> 24 ];
-# endif
- crc ^= *b++;
# ifdef __LITTLE_ENDIAN
- crc = (crc>>8) ^ crc32table_be[ crc & 0xff ];
- crc = (crc>>8) ^ crc32table_be[ crc & 0xff ];
- crc = (crc>>8) ^ crc32table_be[ crc & 0xff ];
- crc = (crc>>8) ^ crc32table_be[ crc & 0xff ];
+# define DO_CRC crc = (crc>>8) ^ tab[ crc & 255 ]
+# define ENDIAN_SHIFT 24
# else
- crc = (crc<<8) ^ crc32table_be[ crc >> 24 ];
- crc = (crc<<8) ^ crc32table_be[ crc >> 24 ];
- crc = (crc<<8) ^ crc32table_be[ crc >> 24 ];
- crc = (crc<<8) ^ crc32table_be[ crc >> 24 ];
+# define DO_CRC crc = (crc<<8) ^ tab[ crc >> 24 ]
+# define ENDIAN_SHIFT 0
# endif
+
+ crc = __cpu_to_be32(crc);
+ /* Align it */
+ if(unlikely(((long)b)&3 && len)){
+ do {
+ crc ^= *((u8 *)b)++ << ENDIAN_SHIFT;
+ DO_CRC;
+ } while ((--len) && ((long)b)&3 );
+ }
+ if(likely(len >= 4)){
+ /* load data 32 bits wide, xor data 32 bits wide. */
+ size_t save_len = len & 3;
+ len = len >> 2;
+ --b; /* use pre increment below(*++b) for speed */
+ do {
+ crc ^= *++b;
+ DO_CRC;
+ DO_CRC;
+ DO_CRC;
+ DO_CRC;
+ } while (--len);
+ b++; /* point to next byte(s) */
+ len = save_len;
}
/* And the last few bytes */
- e = (u32 *)((u8 *)b + (len & 7));
- while (b < e){
-# ifdef __LITTLE_ENDIAN
- crc = (crc>>8) ^ crc32table_be[ (crc ^ *((u8 *)b)++) & 0xff ];
-# else
- crc = (crc<<8) ^ crc32table_be[ crc>>24 ^ *((u8 *)b)++ ];
-# endif
- }
- return __be32_to_cpu(crc) ;
+ if(len){
+ do {
+ crc ^= *((u8 *)b)++ << ENDIAN_SHIFT;
+ DO_CRC;
+ } while (--len);
+ }
+ return __be32_to_cpu(crc);
+#undef ENDIAN_SHIFT
+#undef DO_CRC
+
# elif CRC_BE_BITS == 4
while (len--) {
crc ^= *p++ << 24;

-
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