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The VEX prefix replaces the most commonly used instruction prefix bytes and escape bytes. In many cases, the number of prefix bytes and escape bytes that are replaced is the same as the number of bytes in the VEX prefix, so that the total length of the VEX-encoded instruction is the same as the length of the legacy instruction code.
The VEX prefix can also be used on the legacy SSE instructions giving them a three-operand form, ... AVX-512 Vector Length Extensions ... AVX-512 Byte and Word ...
The EVEX scheme is a 4-byte extension to the VEX scheme which supports the AVX-512 instruction set and allows addressing new 512-bit ZMM registers and new 64-bit operand mask registers. With Advanced Performance Extensions , the Extended EVEX prefix redefines the semantics of several payload bits.
FMA4 instructions are encoded with the VEX prefix, on the form VEX.66.0F3A xx /r ib (no EVEX encodings are defined). The opcode byte xx uses its bottom bit to select floating-point format (0=FP32, 1=FP64) and the remaining bits to select one of the 10 fused-multiply-add operations to perform. For FMA4, operand ordering is controlled by the VEX ...
The VEX prefix used by AVX and AVX2, while flexible, did not leave enough room for the features Intel wanted to add to AVX-512. This has led them to define a new prefix called EVEX. Compared to VEX, EVEX adds the following benefits: [7] Expanded register encoding allowing 32 512-bit registers.
The XOP instructions have an opcode byte 8F (hexadecimal), but otherwise almost identical coding scheme as AVX with the 3-byte VEX prefix. Commentators [4] have seen this as evidence that Intel has not allowed AMD to use any part of the large VEX coding space. AMD has been forced to use different codes in order to avoid using any code ...
160 bits (20 bytes) – maximum key length of the SHA-1, standard Tiger (hash function), and Tiger2 cryptographic message digest algorithms 2 8: 256 bits (32 bytes) – minimum key length for the recommended strong cryptographic message digests as of 2004 – size of an AVX2 vector register, present on newer x86-64 CPUs 2 9: 512 bits (64 bytes)
For each byte-lane, the byte in src3 is used to index into this 32-byte vector and transform the element: bits 4:0 is used to pick one of the 32 bytes. bits 7:6 specify a transform to perform on the byte (0=keep, 1=bitreverse, 2=set-to-zero, 3=replicate-MSB) bit 5, if set, inverts the result after the transform. VPPERM xmm1,xmm2,xmm3/m128,xmm4