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| author | Christophe Leroy <christophe.leroy@c-s.fr> | 2018-04-10 08:34:35 +0200 |
|---|---|---|
| committer | Michael Ellerman <mpe@ellerman.id.au> | 2018-06-04 00:39:16 +1000 |
| commit | 55a0edf083022e402042255a0afb03d0b3a63a9b (patch) | |
| tree | ea021ba22754b8d7393228e8db9dda57f55b13a0 /arch/powerpc | |
| parent | c865c955878eb56d4f37d7ab82438b68fbac4201 (diff) | |
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 <christophe.leroy@c-s.fr>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Diffstat (limited to 'arch/powerpc')
| -rw-r--r-- | arch/powerpc/include/asm/checksum.h | 7 |
1 files changed, 2 insertions, 5 deletions
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 <asm-generic/checksum.h> #else +#include <linux/bitops.h> /* * 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, |