patch-2.4.0-test12 linux/arch/alpha/lib/checksum.c

• Lines: 46
• Date: Mon Dec 11 13:46:26 2000
• Orig file: v2.4.0-test11/linux/arch/alpha/lib/checksum.c
• Orig date: Tue Apr 28 22:28:10 1998

diff -u --recursive --new-file v2.4.0-test11/linux/arch/alpha/lib/checksum.c linux/arch/alpha/lib/checksum.c
@@ -3,6 +3,10 @@
  *
  * This file contains network checksum routines that are better done
  * in an architecture-specific manner due to speed..
+ * Comments in other versions indicate that the algorithms are from RFC1071
+ *
+ * accellerated versions (and 21264 assembly versions ) contributed by
+ *	Rick Gorton	<rick.gorton@alpha-processor.com>
  */
  
 #include <linux/string.h>
@@ -11,15 +15,25 @@
 
 static inline unsigned short from64to16(unsigned long x)
 {
-	/* add up 32-bit words for 33 bits */
-	x = (x & 0xffffffff) + (x >> 32);
-	/* add up 16-bit and 17-bit words for 17+c bits */
-	x = (x & 0xffff) + (x >> 16);
-	/* add up 16-bit and 2-bit for 16+c bit */
-	x = (x & 0xffff) + (x >> 16);
-	/* add up carry.. */
-	x = (x & 0xffff) + (x >> 16);
-	return x;
+	/* Using extract instructions is a bit more efficient
+	   than the original shift/bitmask version.  */
+
+	union {
+		unsigned long	ul;
+		unsigned int	ui[2];
+		unsigned short	us[4];
+	} in_v, tmp_v, out_v;
+
+	in_v.ul = x;
+	tmp_v.ul = (unsigned long) in_v.ui[0] + (unsigned long) in_v.ui[1];
+
+	/* Since the bits of tmp_v.sh[3] are going to always be zero,
+	   we don't have to bother to add that in.  */
+	out_v.ul = (unsigned long) tmp_v.us[0] + (unsigned long) tmp_v.us[1]
+			+ (unsigned long) tmp_v.us[2];
+
+	/* Similarly, out_v.us[2] is always zero for the final add.  */
+	return out_v.us[0] + out_v.us[1];
 }
 
 /*