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Message-ID: <4E4309EF.3090900@systemfabricworks.com>
Date: Wed, 10 Aug 2011 17:45:03 -0500
From: Bob Pearson <rpearson@...temfabricworks.com>
To: linux-kernel@...r.kernel.org, joakim.tjernlund@...nsmode.se,
akpm@...ux-foundation.org, linux@...izon.com,
fzago@...temfabricworks.com
Subject: [patch v5 8/8] crc32-final-cleanup.diff
Some final cleanup changes
- added a comment at the top of crc32.c
- moved macros ahead of function prototype
- replaced loops with for (i = 0; i < xxx; i++) which
requires fewer instructions on x86 since the
buffer lookups can use i as an index.
Signed-off-by: Bob Pearson <rpearson@...temfabricworks.com>
---
lib/crc32.c | 89 ++++++++++++++++++++++++++++--------------------------------
1 file changed, 43 insertions(+), 46 deletions(-)
Index: infiniband/lib/crc32.c
===================================================================
--- infiniband.orig/lib/crc32.c
+++ infiniband/lib/crc32.c
@@ -1,4 +1,8 @@
/*
+ * Aug 8, 2011 Bob Pearson with help from Joakim Tjernlund and George Spelvin
+ * cleaned up code to current version of sparse and added the slicing-by-8
+ * algorithm to the closely similar existing slicing-by-4 algorithm.
+ *
* Oct 15, 2000 Matt Domsch <Matt_Domsch@...l.com>
* Nicer crc32 functions/docs submitted by linux@...izon.com. Thanks!
* Code was from the public domain, copyright abandoned. Code was
@@ -45,45 +49,41 @@ MODULE_LICENSE("GPL");
#if CRC_LE_BITS > 8 || CRC_BE_BITS > 8
-/* implements slicing-by-4 or slicing-by-8 algorithm */
-static inline u32
-crc32_body(u32 crc, unsigned char const *buf, size_t len, const u32 (*tab)[256])
-{
# ifdef __LITTLE_ENDIAN
# define DO_CRC(x) (crc = t0[(crc ^ (x)) & 255] ^ (crc >> 8))
-# define DO_CRC4 crc = t3[(crc) & 255] ^ \
- t2[(crc >> 8) & 255] ^ \
- t1[(crc >> 16) & 255] ^ \
- t0[(crc >> 24) & 255]
-# define DO_CRC8a (t7[(q) & 255] ^ \
- t6[(q >> 8) & 255] ^ \
- t5[(q >> 16) & 255] ^ \
- t4[(q >> 24) & 255])
-# define DO_CRC8b (t3[(q) & 255] ^ \
+# define DO_CRC4 (t3[(q) & 255] ^ \
t2[(q >> 8) & 255] ^ \
t1[(q >> 16) & 255] ^ \
t0[(q >> 24) & 255])
+# define DO_CRC8 (t7[(q) & 255] ^ \
+ t6[(q >> 8) & 255] ^ \
+ t5[(q >> 16) & 255] ^ \
+ t4[(q >> 24) & 255])
# else
# define DO_CRC(x) (crc = t0[((crc >> 24) ^ (x)) & 255] ^ (crc << 8))
-# define DO_CRC4 crc = t0[(crc) & 255] ^ \
- t1[(crc >> 8) & 255] ^ \
- t2[(crc >> 16) & 255] ^ \
- t3[(crc >> 24) & 255]
-# define DO_CRC8a (t4[(q) & 255] ^ \
- t5[(q >> 8) & 255] ^ \
- t6[(q >> 16) & 255] ^ \
- t7[(q >> 24) & 255])
-# define DO_CRC8b (t0[(q) & 255] ^ \
+# define DO_CRC4 (t0[(q) & 255] ^ \
t1[(q >> 8) & 255] ^ \
t2[(q >> 16) & 255] ^ \
t3[(q >> 24) & 255])
+# define DO_CRC8 (t4[(q) & 255] ^ \
+ t5[(q >> 8) & 255] ^ \
+ t6[(q >> 16) & 255] ^ \
+ t7[(q >> 24) & 255])
# endif
+
+/* implements slicing-by-4 or slicing-by-8 algorithm */
+static inline u32 crc32_body(u32 crc, unsigned char const *buf,
+ size_t len, const u32 (*tab)[256])
+{
const u32 *b;
const u32 *t0 = tab[0], *t1 = tab[1], *t2 = tab[2], *t3 = tab[3];
const u32 *t4 = tab[4], *t5 = tab[5], *t6 = tab[6], *t7 = tab[7];
+ u8 *p;
+ u32 q;
size_t init_len;
size_t middle_len;
size_t rem_len;
+ size_t i;
/* break buf into init_len bytes before and
* rem_len bytes after a middle section with
@@ -99,37 +99,34 @@ crc32_body(u32 crc, unsigned char const rem_len = (len - init_len) & 7;
# endif
- /* Align it */
- if (unlikely(init_len)) {
- do {
- DO_CRC(*buf++);
- } while (--init_len);
- }
- b = (const u32 *)buf;
- for (--b; middle_len; --middle_len) {
+ /* process unaligned initial bytes */
+ for (i = 0; i < init_len; i++)
+ DO_CRC(*buf++);
+
+ /* process aligned words */
+ b = (const u32 *)(buf - 4);
+
+ for (i = 0; i < middle_len; i++) {
# if CRC_LE_BITS == 32
- crc ^= *++b; /* use pre increment for speed */
- DO_CRC4;
+ /* slicing-by-4 algorithm */
+ q = crc ^ *++b; /* use pre increment for speed */
+ crc = DO_CRC4;
# else
- u32 q;
+ /* slicing-by-8 algorithm */
q = crc ^ *++b;
- crc = DO_CRC8a;
+ crc = DO_CRC8;
q = *++b;
- crc ^= DO_CRC8b;
+ crc ^= DO_CRC4;
# endif
}
- /* And the last few bytes */
- if (rem_len) {
- u8 *p = (u8 *)(b + 1) - 1;
- do {
- DO_CRC(*++p); /* use pre increment for speed */
- } while (--rem_len);
- }
+
+ /* process unaligned remaining bytes */
+ p = (u8 *)(b + 1) - 1;
+
+ for (i = 0; i < rem_len; i++)
+ DO_CRC(*++p); /* use pre increment for speed */
+
return crc;
-#undef DO_CRC
-#undef DO_CRC4
-#undef DO_CRC8a
-#undef DO_CRC8b
}
#endif
--
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