From 55a0edf083022e402042255a0afb03d0b3a63a9b Mon Sep 17 00:00:00 2001 From: Christophe Leroy Date: Tue, 10 Apr 2018 08:34:35 +0200 Subject: powerpc/64: optimises from64to32() The current implementation of from64to32() gives a poor result: 0000000000000270 <.from64to32>: 270: 38 00 ff ff li r0,-1 274: 78 69 00 22 rldicl r9,r3,32,32 278: 78 00 00 20 clrldi r0,r0,32 27c: 7c 60 00 38 and r0,r3,r0 280: 7c 09 02 14 add r0,r9,r0 284: 78 09 00 22 rldicl r9,r0,32,32 288: 7c 00 4a 14 add r0,r0,r9 28c: 78 03 00 20 clrldi r3,r0,32 290: 4e 80 00 20 blr This patch modifies from64to32() to operate in the same spirit as csum_fold() It swaps the two 32-bit halves of sum then it adds it with the unswapped sum. If there is a carry from adding the two 32-bit halves, it will carry from the lower half into the upper half, giving us the correct sum in the upper half. The resulting code is: 0000000000000260 <.from64to32>: 260: 78 60 00 02 rotldi r0,r3,32 264: 7c 60 1a 14 add r3,r0,r3 268: 78 63 00 22 rldicl r3,r3,32,32 26c: 4e 80 00 20 blr Signed-off-by: Christophe Leroy Signed-off-by: Michael Ellerman --- arch/powerpc/include/asm/checksum.h | 7 ++----- 1 file changed, 2 insertions(+), 5 deletions(-) (limited to 'arch/powerpc/include/asm/checksum.h') diff --git a/arch/powerpc/include/asm/checksum.h b/arch/powerpc/include/asm/checksum.h index 4e63787dc3be..54065caa40b3 100644 --- a/arch/powerpc/include/asm/checksum.h +++ b/arch/powerpc/include/asm/checksum.h @@ -12,6 +12,7 @@ #ifdef CONFIG_GENERIC_CSUM #include #else +#include /* * Computes the checksum of a memory block at src, length len, * and adds in "sum" (32-bit), while copying the block to dst. @@ -55,11 +56,7 @@ static inline __sum16 csum_fold(__wsum sum) static inline u32 from64to32(u64 x) { - /* add up 32-bit and 32-bit for 32+c bit */ - x = (x & 0xffffffff) + (x >> 32); - /* add up carry.. */ - x = (x & 0xffffffff) + (x >> 32); - return (u32)x; + return (x + ror64(x, 32)) >> 32; } static inline __wsum csum_tcpudp_nofold(__be32 saddr, __be32 daddr, __u32 len, -- cgit v1.2.3-59-g8ed1b