# ROUNDSD (Round Scalar Double Precision Floating-Point Values)

## Opcodes

Opcode*/Instruction | Op/En | 64/32 bit Mode Support | CPUID Feature Flag | Description |
---|---|---|---|---|

66 0F 3A 0B /r ib ROUNDSD xmm1, xmm2/m64, imm8 |
RMI | V/V | SSE4_1 | Round the low packed double precision floating-point value in xmm2/m64 and place the result in xmm1. The rounding mode is determined by imm8. |

VEX.NDS.LIG.66.0F3A.WIG 0B /r ib VROUNDSD xmm1, xmm2, xmm3/m64, imm8 |
RVMI | V/V | AVX | Round the low packed double precision floating-point value in xmm3/m64 and place the result in xmm1. The rounding mode is determined by imm8. Upper packed double precision floating-point value (bits[127:64]) from xmm2 is copied to xmm1[127:64]. |

## Instruction Operand Encoding

Op/En | Operand 1 | Operand 2 | Operand 3 | Operand 4 |
---|---|---|---|---|

RMI | ModRM:reg (w) | ModRM:r/m (r) | imm8 | NA |

RVMI | ModRM:reg (w) | VEX.vvvv (r) | ModRM:r/m (r) | imm8 |

## Description

Round the DP FP value in the lower qword of the source operand (second operand) using the rounding mode spec-ified in the immediate operand (third operand) and place the result in the destination operand (first operand). The rounding process rounds a double-precision floating-point input to an integer value and returns the integer result as a double precision floating-point value in the lowest position. The upper double precision floating-point value in the destination is retained.

The immediate operand specifies control fields for the rounding operation, three bit fields are defined and shown in Figure 4-20. Bit 3 of the immediate byte controls processor behavior for a precision exception, bit 2 selects the source of rounding mode control. Bits 1:0 specify a non-sticky rounding-mode value (Table 4-15 lists the encoded values for rounding-mode field).

The Precision Floating-Point Exception is signaled according to the immediate operand. If any source operand is an SNaN then it will be converted to a QNaN. If DAZ is set to ‘1 then denormals will be converted to zero before rounding.

128-bit Legacy SSE version: The first source operand and the destination operand are the same. Bits (VLMAX-1:64) of the corresponding YMM destination register remain unchanged.

VEX.128 encoded version: Bits (VLMAX-1:128) of the destination YMM register are zeroed.

## Operation

IF (imm[2] = ‘1) THEN // rounding mode is determined by MXCSR.RC DEST[63:0] ← ConvertDPFPToInteger_M(SRC[63:0]); ELSE // rounding mode is determined by IMM8.RC DEST[63:0] ← ConvertDPFPToInteger_Imm(SRC[63:0]); FI; DEST[127:63] remains unchanged ;

**ROUNDSD (128-bit Legacy SSE version)**

DEST[63:0] ← RoundToInteger(SRC[63:0], ROUND_CONTROL) DEST[VLMAX-1:64] (Unmodified)

**VROUNDSD (VEX.128 encoded version)**

DEST[63:0] ← RoundToInteger(SRC2[63:0], ROUND_CONTROL) DEST[127:64] ← SRC1[127:64] DEST[VLMAX-1:128] ← 0

## Intel C/C++ Compiler Intrinsic Equivalent

ROUNDSD:

__m128d mm_round_sd(__m128d dst, __m128d s1, int iRoundMode); __m128d mm_floor_sd(__m128d dst, __m128d s1); __m128d mm_ceil_sd(__m128d dst, __m128d s1);

## SIMD Floating-Point Exceptions

Invalid (signaled only if SRC = SNaN)

Precision (signaled only if imm[3] = ‘0; if imm[3] = ‘1, then the Precision Mask in the MXSCSR is ignored and preci-sion exception is not signaled.)

Note that Denormal is not signaled by ROUNDSD.

## Other Exceptions

See Exceptions Type 3.