Intel® ISA Extensions
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Encoding phsubsw with VEX.256

PFaut2
Beginner
‎06-13-2019 10:48 PM
1,474 Views

Hi,

I don't understand how to encode PHSUBSW with VEX.256. According to the documentation, VEX.L must be 0, otherwise the instruction will #UD. I thought we must use VEX.L = 1 to force the VEX.256.

Thanks

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MarkC_Intel
Moderator
‎06-14-2019 03:30 PM
1,474 Views

Hi. Thanks. Yeah that "VEX.L must be zero" thing is left over from before we introduced AVX2 which added the 256b encoding for this instruction. I'll ask our doc team to fix this (and possibly others that might have similar origin).

 

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