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Extract vector from pair of vectors

Copy the indexed byte up to the last byte of the first source vector to the bottom of the result vector, then fill the remainder of the result starting from the first byte of the second source vector. The result is placed destructively in the destination and first source vector, or constructively in the destination vector. This instruction is unpredicated.

An index that is greater than or equal to the vector length in bytes is treated as zero, resulting in the first source vector being copied to the result unchanged.

The Destructive encoding of this instruction might be immediately preceded in program order by a MOVPRFX instruction. The MOVPRFX instruction must conform to all of the following requirements, otherwise the behavior of the MOVPRFX and this instruction is UNPREDICTABLE: The MOVPRFX instruction must be unpredicated. The MOVPRFX instruction must specify the same destination register as this instruction. The destination register must not refer to architectural register state referenced by any other source operand register of this instruction.

It has encodings from 2 classes: Constructive and Destructive

Constructive

if !HaveSVE2() && !HaveSME() then UNDEFINED; integer esize = 8; integer dst = UInt(Zd); integer s1 = UInt(Zn); integer s2 = (s1 + 1) MOD 32; integer position = UInt(imm8h:imm8l);

Destructive

if !HaveSVE() && !HaveSME() then UNDEFINED; integer esize = 8; integer dst = UInt(Zdn); integer s1 = dst; integer s2 = UInt(Zm); integer position = UInt(imm8h:imm8l);