BLSMSK (Intel x86/64 assembly instruction)

모두의 코드
BLSMSK (Intel x86/64 assembly instruction)

작성일 : 2020-09-01 이 글은 771 번 읽혔습니다.

BLSMSK

Get Mask Up to Lowest Set Bit

참고 사항

아래 표를 해석하는 방법은 x86-64 명령어 레퍼런스 읽는 법 글을 참조하시기 바랍니다.

Opcode/Instruction	Op/ En	64/32 -bit Mode	CPUID Feature Flag	Description
`VEX.NDD.LZ.0F38.W0 F3 /2` BLSMSK r32 r/m32	VM	V/V	BMI1	Set all lower bits in r32 to "1" starting from bit 0 to lowest set bit in r/m32.
`VEX.NDD.LZ.0F38.W1 F3 /2` BLSMSK r64 r/m64	VM	V/N.E.	BMI1	Set all lower bits in r64 to "1" starting from bit 0 to lowest set bit in r/m64.

Instruction Operand Encoding

Op/En	Operand 1	Operand 2	Operand 3	Operand 4
VM	VEX.vvvv (w)	ModRM:r/m (r)	NA	NA

Description

Sets all the lower bits of the destination operand to "1" up to and including lowest set bit (=1) in the source operand. If source operand is zero, BLSMSK sets all bits of the destination operand to 1 and also sets CF to 1.

This instruction is not supported in real mode and virtual-8086 mode. The operand size is always 32 bits if not in 64-bit mode. In 64-bit mode operand size 64 requires VEX.W1. VEX.W1 is ignored in non-64-bit modes. An attempt to execute this instruction with VEX.L not equal to 0 will cause #UD.

Operation

temp <- (SRC-1) XOR (SRC) ;
SF <- temp[OperandSize -1];
ZF <- 0;
IF SRC = 0
    CF <- 1;
ELSE
    CF <- 0;
FI
DEST <- temp;

Flags Affected

SF is updated based on the result. CF is set if the source if zero. ZF and OF flags are cleared. AF and PF flag are undefined.

Intel C/C++ Compiler Intrinsic Equivalent

BLSMSK : unsigned __int32 _blsmsk_u32(unsigned __int32 src);
BLSMSK : unsigned __int64 _blsmsk_u64(unsigned __int64 src);

SIMD Floating-Point Exceptions

None

Other Exceptions

See Section 2.5.1, "Exception Conditions for VEX-Encoded GPR Instructions", Table 2-29; additionally

#UD If VEX.W = 1.

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모두의 코드 BLSMSK (Intel x86/64 assembly instruction)