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Unlike the rest of the AVX-512 instructions, these instructions are all VEX encoded. The initial opmask instructions are all 16-bit (Word) versions. With AVX-512DQ 8-bit (Byte) versions were added to better match the needs of masking 8 64-bit values, and with AVX-512BW 32-bit (Double) and 64-bit (Quad) versions were added so they can mask up to ...
The REX prefix provides additional space for encoding 64-bit addressing modes and additional registers present in the x86-64 architecture. Bit-field W changes the operand size to 64 bits, R expands reg to 4 bits, B expands r/m (or opreg in the few opcodes that encode the register in the 3 lowest opcode bits, such as "POP reg"), and X and B expand index and base in the SIB byte.
The EVEX prefix retains fields introduced in the VEX prefix: Four bits R̅, X̅, B̅ and W from the VEX prefix, stored in inverted form. W expands the operand size to 64 bits or serves as an additional opcode, R expands reg, B expands r/m or reg, and X and B expand index and base in the SIB byte. Four bits named v̅, stored in inverted form.
VEX coding is also used for instructions operating on the k0-k7 mask registers that were introduced with AVX-512. The alignment requirement of SIMD memory operands is relaxed. [5] Unlike their non-VEX coded counterparts, most VEX coded vector instructions no longer require their memory operands to be aligned to the vector size.
AMD was the first to introduce the instructions that now form Intel's BMI1 as part of its ABM (Advanced Bit Manipulation) instruction set, then later added support for Intel's new BMI2 instructions. AMD today advertises the availability of these features via Intel's BMI1 and BMI2 cpuflags and instructs programmers to target them accordingly.
The use of the 8F byte requires that the m-bits (see VEX coding scheme) have a value larger than or equal to 8 in order to avoid overlap with existing instructions. [Note 1] The C4 byte used in the VEX scheme has no such restriction. This may prevent the use of the m-bits for other purposes in the future in the XOP scheme, but not in the VEX ...
3. Keebler Fudge Magic Middles. Neither the chocolate fudge cream inside a shortbread cookie nor versions with peanut butter or chocolate chip crusts survived.
The actual number of instructions executed in 1 second was about 500,000, which led to complaints of marketing exaggeration. The result was the definition of a "VAX MIPS", the speed of a VAX-11/780; a computer performing at 27 VAX MIPS would run the same program roughly 27 times faster than the VAX-11/780.