VEX prefix

The VEX prefix (from "vector extensions") and VEX coding scheme are an extension to the x86-64 instruction set architecture for microprocessors from Intel, AMD and others. It was introduced with the AVX instruction set.

The VEX prefix consists of three bytes and can be added to new and existing instructions. It is a superset of the REX prefix and provides 16 bits of payload in total. The VEX prefix can also be encoded into a shorter two-byte variant, if the omitted bits have specific values.

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