On Tue, 2020-02-11 at 01:28 -0300, Leonardo Bras wrote: > Looks a valid change. > rlwimi r10, r10, 0, 0x0f00 means: > r10 = ((r10 << 0) & 0x0f00) | (r10 & ~0x0f00) which ends up being > r10 = r10 > > On ISA, rlwinm is recommended for clearing high order bits. > rlwinm r10, r10, 0, ~0x0f00 means: > r10 = (r10 << 0) & ~0x0f00 > > Which does exactly what the comments suggests. > > FWIW: > Reviwed-by: Leonardo Bras <leona...@linux.ibm.com>
Sorry, I just realized the above was not very clear on my part. What I meant to say was: I think your change is correct, as it correctly fixes this line. I would suggest adding the text bellow to your commit message, making it easier to understand why rlwimi is not the right instruction clear bytes 20-23, and why rlwinm is. The current instruction can be translated to C as: rlwimi r10, r10, 0, 0x0f00 r10 = ((r10 << 0) & 0x0f00) | (r10 & ~0x0f00) -> r10 = (r10 & 0x0f00) | (r10 & ~0x0f00) -> r10 = r10 The new proposed instruction can be translated to C as: rlwinm r10, r10, 0, ~0x0f00 -> r10 = (r10 << 0) & ~0x0f00 Which clears bits 20-23 as comment on code states. Best regards, Leonardo Bras
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