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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.
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. vvvv specifies a second non-destructive source register operand.
existing instructions extended to a 64 bit operand size (remaining instructions) Most instructions with a 64 bit operand size encode this using a REX.W prefix; in the absence of the REX.W prefix, the corresponding instruction with 32 bit operand size is encoded. This mechanism also applies to most other instructions with 32 bit operand size.
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 U.S. Food and Drug Administration (FDA) now classifies eggs as a “healthy, nutrient-dense" food, according to a new proposed rule. Registered dietitians react to the change.
Wawa and a police carThis guy gave new meaning to the slogan “Gottahava Wawa.” Police in East Windsor, N.J., arrested a 24-year-old man on Dec. 23, and charged him with...
How To Make The Best Crab Cakes. I’ve learned a few things about them over the years. The best ones are made with a mix of fresh-picked jumbo lump and regular lump crab.Don’t bother with the ...
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 ...