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Henk-Jan Lebbink edited this page Jun 5, 2018 · 13 revisions

ROUNDSD — Round Scalar Double Precision Floating-Point Values

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 4-24. 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 4-18 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 (MAXVL- 1:64) of the corresponding YMM destination register remain unchanged.

VEX.128 encoded version: Bits (MAXVL-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[MAXVL-1:64] (Unmodified)

VROUNDSD (VEX.128 encoded version)

DEST[63:0] ← RoundToInteger(SRC2[63:0], ROUND_CONTROL)
DEST[127:64] ← SRC1[127:64]
DEST[MAXVL-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 precision exception is not signaled.)

Note that Denormal is not signaled by ROUNDSD.

Other Exceptions

See Exceptions Type 3.

Source: Intel® Architecture Software Developer's Manual (May 2018)
Generated: 5-6-2018

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