[patch v3 7/7] crc32: final-cleanup.diff

[Bob Pearson]

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@xxxxxxxxxxxxxxxxxxxxx>

---
 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@xxxxxxxx>
  * Nicer crc32 functions/docs submitted by linux@xxxxxxxxxxxx  Thanks!
  * Code was from the public domain, copyright abandoned.  Code was
@@ -45,43 +49,39 @@ 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 = tab[0][(crc ^ (x)) & 255] ^ (crc >> 8)
-#  define DO_CRC4 crc = tab[3][(crc) & 255] ^ \
-		tab[2][(crc >> 8) & 255] ^ \
-		tab[1][(crc >> 16) & 255] ^ \
-		tab[0][(crc >> 24) & 255]
-#  define DO_CRC8a (tab[7][(q) & 255] ^ \
-		tab[6][(q >> 8) & 255] ^ \
-		tab[5][(q >> 16) & 255] ^ \
-		tab[4][(q >> 24) & 255])
-#  define DO_CRC8b (tab[3][(q) & 255] ^ \
+#  define DO_CRC4 (tab[3][(q) & 255] ^ \
 		tab[2][(q >> 8) & 255] ^ \
 		tab[1][(q >> 16) & 255] ^ \
 		tab[0][(q >> 24) & 255])
+#  define DO_CRC8 (tab[7][(q) & 255] ^ \
+		tab[6][(q >> 8) & 255] ^ \
+		tab[5][(q >> 16) & 255] ^ \
+		tab[4][(q >> 24) & 255])
 # else
 #  define DO_CRC(x) crc = tab[0][((crc >> 24) ^ (x)) & 255] ^ (crc << 8)
-#  define DO_CRC4 crc = tab[0][(crc) & 255] ^ \
-		tab[1][(crc >> 8) & 255] ^ \
-		tab[2][(crc >> 16) & 255] ^ \
-		tab[3][(crc >> 24) & 255]
-#  define DO_CRC8a (tab[4][(q) & 255] ^ \
-		tab[5][(q >> 8) & 255] ^ \
-		tab[6][(q >> 16) & 255] ^ \
-		tab[8][(q >> 24) & 255])
-#  define DO_CRC8b (tab[0][(q) & 255] ^ \
+#  define DO_CRC4 (tab[0][(q) & 255] ^ \
 		tab[1][(q >> 8) & 255] ^ \
 		tab[2][(q >> 16) & 255] ^ \
 		tab[3][(q >> 24) & 255])
+#  define DO_CRC8 (tab[4][(q) & 255] ^ \
+		tab[5][(q >> 8) & 255] ^ \
+		tab[6][(q >> 16) & 255] ^ \
+		tab[7][(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;
+	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
@@ -96,37 +96,34 @@ 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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