# SQRTSS — Compute Square Root of Scalar Single Precision Value

Opcode/Instruction | Op / En | 64/32 bit Mode Support | CPUID Feature Flag | Description
--- | --- | --- | --- | ---
F3 0F 51 /r SQRTSS xmm1, xmm2/m32 | A | V/V | SSE | Computes square root of the low single precision floating-point value in xmm2/m32 and stores the results in xmm1.
VEX.LIG.F3.0F.WIG 51 /r VSQRTSS xmm1, xmm2, xmm3/m32 | B | V/V | AVX | Computes square root of the low single precision floating-point value in xmm3/m32 and stores the results in xmm1. Also, upper single precision floating-point values (bits[127:32]) from xmm2 are copied to xmm1[127:32].
EVEX.LLIG.F3.0F.W0 51 /r VSQRTSS xmm1 {k1}{z}, xmm2, xmm3/m32{er} | C | V/V | AVX512F | Computes square root of the low single precision floating-point value in xmm3/m32 and stores the results in xmm1 under writemask k1. Also, upper single precision floating-point values (bits[127:32]) from xmm2 are copied to xmm1[127:32].

## Instruction Operand Encoding ¶

Op/En | Tuple Type | Operand 1 | Operand 2 | Operand 3 | Operand 4
--- | --- | --- | --- | --- | ---
A | N/A | ModRM:reg (w) | ModRM:r/m (r) | N/A | N/A
B | N/A | ModRM:reg (w) | VEX.vvvv (r) | ModRM:r/m (r) | N/A
C | Tuple1 Scalar | ModRM:reg (w) | EVEX.vvvv (r) | ModRM:r/m (r) | N/A

## Description ¶

Computes the square root of the low single precision floating-point value in the second source operand and stores the single precision floating-point result in the destination operand. The second source operand can be an XMM register or a 32-bit memory location. The first source and destination operands is an XMM register.

128-bit Legacy SSE version: The first source operand and the destination operand are the same. Bits (MAXVL-1:32) of the corresponding YMM destination register remain unchanged.

VEX.128 and EVEX encoded versions: Bits 127:32 of the destination operand are copied from the corresponding bits of the first source operand. Bits (MAXVL-1:128) of the destination ZMM register are zeroed.

EVEX encoded version: The low doubleword element of the destination operand is updated according to the write-mask.

Software should ensure VSQRTSS is encoded with VEX.L=0. Encoding VSQRTSS with VEX.L=1 may encounter unpredictable behavior across different processor generations.

## Operation ¶

### VSQRTSS (EVEX Encoded Version) ¶

    IF (EVEX.b = 1) AND (SRC2 *is register*)
        THEN
            SET_ROUNDING_MODE_FOR_THIS_INSTRUCTION(EVEX.RC);
        ELSE
            SET_ROUNDING_MODE_FOR_THIS_INSTRUCTION(MXCSR.RC);
    FI;
    IF k1[0] or *no writemask*
        THEN DEST[31:0] := SQRT(SRC2[31:0])
        ELSE
            IF *merging-masking* ; merging-masking
                THEN *DEST[31:0] remains unchanged*
                ELSE ; zeroing-masking
                    DEST[31:0] := 0
            FI;
    FI;
    DEST[127:32] := SRC1[127:32]
    DEST[MAXVL-1:128] := 0

### VSQRTSS (VEX.128 Encoded Version) ¶

    DEST[31:0] := SQRT(SRC2[31:0])
    DEST[127:32] := SRC1[127:32]
    DEST[MAXVL-1:128] := 0

### SQRTSS (128-bit Legacy SSE Version) ¶

    DEST[31:0] := SQRT(SRC2[31:0])
    DEST[MAXVL-1:32] (Unmodified)

## Intel C/C++ Compiler Intrinsic Equivalent ¶

    VSQRTSS __m128 _mm_sqrt_round_ss(__m128 a, __m128 b, int r);

    VSQRTSS __m128 _mm_mask_sqrt_round_ss(__m128 s, __mmask8 k, __m128 a, __m128 b, int r);

    VSQRTSS __m128 _mm_maskz_sqrt_round_ss( __mmask8 k, __m128 a, __m128 b, int r);

    SQRTSS __m128 _mm_sqrt_ss(__m128 a)

## SIMD Floating-Point Exceptions ¶

Invalid, Precision, Denormal.

## Other Exceptions ¶

Non-EVEX-encoded instruction, see Table 2-20, “Type 3 Class Exception Conditions.”

EVEX-encoded instruction, see Table 2-47, “Type E3 Class Exception Conditions.”