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 0What 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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