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[vector crypto] Clarifying mandate for vector register index alignment to LMUL/EMUL #1653

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[vector crypto] Clarifying mandate for vector register index alignment to LMUL/EMUL #1653

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[vector crypto] Clarifying mandate for vector register index alignmen…
nibrunieAtSi5 Sep 26, 2024
5e28050
Applying Andrew's feedback
nibrunieAtSi5 Sep 26, 2024
6cf2aa0
Update src/vector-crypto.adoc
nibrunieAtSi5 Sep 26, 2024
73618e3
fixing typo
nibrunieAtSi5 Oct 17, 2024
c7f0dd2
Review feedback: rewording the note (and fixing the too permissing ph…
nibrunieAtSi5 Oct 18, 2024
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9 changes: 9 additions & 0 deletions src/vector-crypto.adoc
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Expand Up @@ -269,6 +269,15 @@ Element Group Size (`EGS`).
LMUL constraints::
For element-group instructions, `LMUL`*`VLEN` must always be at least as large as `EGW`, otherwise an
_illegal instruction exception_ is raised, even if `vl`=0.
+
A *Vector Element Group* operand or destination has `EMUL = LMUL`.
+
A *Scalar Element Group* operand or destination has `EMUL = ceil(EGW / VLEN)`.
+
[NOTE]
====
These `EMUL` alignement constraints allow scalar element group operands to be allocated to any vector register (without need to be aligned to `LMUL`) for any implementation with `VLEN >= EGW`.
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