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Is there some instruction to do shift to left by the number from mask register somehow?

denbianh
Beginner
129 Views

Hi experts,

Now I want a process like psllw(d/q) behavior, but COUNT can be unequal for each word(dword/qword etc).

How can I do that, any instruction or instruction pairs can be use?

Appreciate if you can give me some tips/hints.

Thank you in advance.

-Steven

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3 Replies
denbianh
Beginner
129 Views
Here I will provide the sample to make this question much clearer: Assume Bi (0-7) for Byte(s) in some xmm0 register in LSB, xmm0 = 00 00 00 00 00 00 00 00 B7 B6 B5 B4 B3 B2 B1 B0 How can I get desired result? like, xmm1 = (B7<<7) (B6<<6) (B5<<5) (B4<<4) (B3<<3) (B2<<2) (B1<<1) (B0<<0) Thanks.
sirrida
Beginner
129 Views
Let me propose to simulate the shifting via PMULLW (SSE 2) or PMULLD (SSE 4.1) as a poor replacement. When AVX2 becomes available you can apply the commands VPSLLVD and VPSLLVQ. Alternatively AMD provides the commands VPSHL(B/W/D/Q) with their new XOP commands.
denbianh
Beginner
129 Views
Thanks Sirrida for your answer here. It is very valuable for me to follow this.
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