SARX/SHLX/SHRX - Shift Without Affecting Flags

Opcode/ Instruction

Op/ En

64/32- bit Mode

CPUID Feature Flag

Description

VEX.LZ.F3.0F38.W0 F7 /r SARX r32a, r/m32, r32b

RMV

V/V

BMI2

Shift r/m32 arithmetically right with count specified in r32b.

VEX.LZ.66.0F38.W0 F7 /r SHLX r32a, r/m32, r32b

RMV

V/V

BMI2

Shift r/m32 logically left with count specified in r32b.

VEX.LZ.F2.0F38.W0 F7 /r SHRX r32a, r/m32, r32b

RMV

V/V

BMI2

Shift r/m32 logically right with count specified in r32b.

VEX.LZ.F3.0F38.W1 F7 /r SARX r64a, r/m64, r64b

RMV

V/N.E.

BMI2

Shift r/m64 arithmetically right with count specified in r64b.

VEX.LZ.66.0F38.W1 F7 /r SHLX r64a, r/m64, r64b

RMV

V/N.E.

BMI2

Shift r/m64 logically left with count specified in r64b.

VEX.LZ.F2.0F38.W1 F7 /r SHRX r64a, r/m64, r64b

RMV

V/N.E.

BMI2

Shift r/m64 logically right with count specified in r64b.

Instruction Operand Encoding

Op/En

Operand 1

Operand 2

Operand 3

Operand 4

RMV

ModRM:reg (w)

ModRM:r/m (r)

VEX.vvvv (r)

N/A

Description

Shifts the bits of the first source operand (the second operand) to the left or right by a COUNT value specified in the second source operand (the third operand). The result is written to the destination operand (the first operand).

The shift arithmetic right (SARX) and shift logical right (SHRX) instructions shift the bits of the destination operand to the right (toward less significant bit locations), SARX keeps and propagates the most significant bit (sign bit) while shifting.

The logical shift left (SHLX) shifts the bits of the destination operand to the left (toward more significant bit loca- tions).

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.

If the value specified in the first source operand exceeds OperandSize -1, the COUNT value is masked.

SARX,SHRX, and SHLX instructions do not update flags.

Operation 

TEMP := SRC1;
IF VEX.W1 and CS.L = 1
THEN
   countMASK := 3FH;
ELSE
   countMASK := 1FH;
FI
COUNT := (SRC2 AND countMASK)
DEST[OperandSize -1] = TEMP[OperandSize -1];
DO WHILE (COUNT != 0)
   IF instruction is SHLX
       THEN
            DEST[] := DEST *2;
       ELSE IF instruction is SHRX
            THEN
                DEST[] := DEST /2; //unsigned divide
       ELSE         // SARX
                DEST[] := DEST /2; // signed divide, round toward negative infinity
   FI;
   COUNT := COUNT - 1;
OD

Flags Affected

None.

Intel C/C++ Compiler Intrinsic Equivalent 

Auto-generated from high-level language.

SIMD Floating-Point Exceptions

None.

Other Exceptions

See Table 2-29, "Type 13 Class Exception Conditions."