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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 ...
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 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.
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.
Below is the full 8086/8088 instruction set of Intel (81 instructions total). [2] These instructions are also available in 32-bit mode, in which they operate on 32-bit registers (eax, ebx, etc.) and values instead of their 16-bit (ax, bx, etc.) counterparts.
Commonly, a decimal SI metric prefix (such as kilo-) is used with bit and byte to express larger sizes (kilobit, kilobyte). But, this is usually inaccurate since these prefixes are decimal, whereas binary hardware size is usually binary. Customarily, each metric prefix, 1000 n, is used to mean a close approximation of a binary multiple, 1024 n ...
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 ...