PowerPC和clrlslwi -or-rlwinm指令 [英] PowerPC and the clrlslwi -or- rlwinm instruction

问题描述

我已经在这里阅读了其他文章，但是仍然对PPC和rlwinm有疑问.

I've read the other posts here, but still have a question about PPC and rlwinm.

我正在查看的示例是:

li  r0, 0x100
clrlslwi  r9, r0, 27,5 (which afaik is the same as rlwinm r9, r0,5,22,26)

首先我加载r0 = 0x100 然后将r0左移5，因此r0 = 0x2000(无溢出，因此无需旋转)

First I load r0 = 0x100 Then Left Shift r0 by 5 so r0 = 0x2000 (No overflow, so no rotate needed)

使用第22到26位设为0x3e0设置掩码

Make a Mask with bits 22 to 26 set = 0x3e0

使用掩码= 0x2000和0x3E0 = 0的AND r0

AND r0 with the Mask = 0x2000 AND 0x3E0 = 0

我一定做错了...这将始终为0 我想念什么?

I must be doing something wrong...this would always net 0 What am I missing?

推荐答案

是的(清除左单词并立即左移单词)

yes that's true (Clear left and shift left word immediate)

clrlslwi rA,rS,b,n (n ≤ b ≤ 31) = rlwinm rA,rS,n,b – n,31 – n

所以 clrlslwi r9, r0, 27,5 = rlwinm r9, r0, 5, 22(27-5), 26(31-5)

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