Fix semantics of SHLD_16, SHRD_16, and VPSxLV #520
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vbgl
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When the (masked) shift amount is larger than the operand size, the result is undefined. This is soundly approximated in the semantics by throwing a type error. Note that it is not necessary to fix the EasyCrypt model: it is meant to be correct for safe executions only.
These instructions are available for vector elements of size 16-bit.
bgregoir
approved these changes
Jul 17, 2023
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Caveat: the 16-bit variants of VPSLLV and VPSRLV belong to the instruction-set extension AVX-512 byte-and-word instructions (BW). |
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When the (masked) shift amount is larger than the operand size, the result is undefined. This is soundly approximated in the semantics by throwing a type error.
I still have to check whether SHLD has the same issue.
Found by random testing.