Unverified Commit 1e7196fa authored by Charlie Jenkins's avatar Charlie Jenkins Committed by Palmer Dabbelt
Browse files

asm-generic: Improve csum_fold 



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: default avatarCharlie Jenkins <charlie@rivosinc.com>
Reviewed-by: default avatarDavid Laight <david.laight@aculab.com>
Link: https://lore.kernel.org/r/20240108-optimize_checksum-v15-1-1c50de5f2167@rivosinc.com


Signed-off-by: default avatarPalmer Dabbelt <palmer@rivosinc.com>
parent b85ea95d

include/asm-generic/checksum.h

+3 −3
Original line number Diff line number Diff line
@@ -2,6 +2,8 @@ 
#ifndef __ASM_GENERIC_CHECKSUM_H

#define __ASM_GENERIC_CHECKSUM_H



#include <linux/bitops.h>



/*

 * computes the checksum of a memory block at buff, length len,

 * and adds in "sum" (32-bit)
@@ -31,9 +33,7 @@ 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