This csum_fold implementation introduced into arch/arc by Vineet Gupta
is better than the default implementation on at least arc, x86, and
riscv. Using GCC trunk and compiling non-inlined version, this
implementation has 41.6667%, 25% fewer instructions on riscv64, x86-64
respectively with -O3 optimization. Most implmentations override this
default in asm, but this should be more performant than all of those
other implementations except for arm which has barrel shifting and
sparc32 which has a carry flag.
Signed-off-by: Charlie Jenkins <charlie@xxxxxxxxxxxx>
Reviewed-by: David Laight <david.laight@xxxxxxxxxx>
---
include/asm-generic/checksum.h | 4 +---
1 file changed, 1 insertion(+), 3 deletions(-)
diff --git a/include/asm-generic/checksum.h b/include/asm-generic/checksum.h
index 43e18db89c14..37f5ec70ac93 100644
--- a/include/asm-generic/checksum.h
+++ b/include/asm-generic/checksum.h
@@ -31,9 +31,7 @@ extern __sum16 ip_fast_csum(const void *iph, unsigned int ihl);
static inline __sum16 csum_fold(__wsum csum)
{
u32 sum = (__force u32)csum;
- sum = (sum & 0xffff) + (sum >> 16);
- sum = (sum & 0xffff) + (sum >> 16);
- return (__force __sum16)~sum;
+ return (__force __sum16)((~sum - ror32(sum, 16)) >> 16);
}
#endif
--
2.42.0
