SARX/SHLX/SHRX — Shift Without Affecting Flags

Instruction Operand Encoding ¶

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 locations).

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.”