[parisc-linux-cvs] checksum.h patch

[Helge Deller]

- The following patch simplyfies the csum_fold() instruction and will expand 
to only 4 assembler statements in the new form instead of 8 assembler 
instructions as before.  So there is no need to convert this any longer to 
inlined assembler, because a) we couldn't do any better and b) the compiler 
will be able to schedule the assembler statements inside the caller code 
better than us.
- csum_fold() should return an uint16 value which it now really does. In the 
previous version the upper 16bits were 0xffff (ah, and why the heck isn't it 
"unsigned __short__ csum_fold()" in all arches ????).

Index: checksum.h
===================================================================
RCS file: /home/cvs/parisc/linux/include/asm-parisc/checksum.h,v
retrieving revision 1.10
diff -u -r1.10 checksum.h
--- checksum.h  2001/04/26 05:01:59     1.10
+++ checksum.h  2001/05/12 16:45:22
@@ -98,9 +98,12 @@
  */
 static inline unsigned int csum_fold(unsigned int sum)
 {
-       sum = (sum & 0xffff) + (sum >> 16);
-       sum = (sum & 0xffff) + (sum >> 16);
-       return ~sum;
+       /* add the swapped two 16-bit halves of sum,
+          a possible carry from adding the two 16-bit halves,
+          will carry from the lower half into the upper half,
+          giving us the correct sum in the upper half. */
+       sum += (sum << 16) + (sum >> 16);
+       return (~sum) >> 16;
 }
 
 static inline unsigned long csum_tcpudp_nofold(unsigned long saddr,