Christophe Leroy 55a0edf083 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>		2018-06-04 00:39:16 +10:00
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asm	powerpc/64: optimises from64to32()	2018-06-04 00:39:16 +10:00
uapi/asm	KVM changes for 4.16	2018-02-10 13:16:35 -08:00