_mm_round_ps

Microsoft Specific

Emits the Streaming SIMD Extensions 4 (SSE4) instruction roundps. This instruction rounds a 32 bit value by using the specified rounding control.

__m128 _mm_round_ps( 
   __m128 a,
   const int cntrl 
);

Parameters

• [in] a
  A 128-bit parameter that contains four 32-bit floating point values.

• [in] cntrl
  A constant that specifies control fields for the rounding operation.

Return value

A 128-bit parameter. The result can be expressed with the following equations:.

r0 := RND(a0)
r1 := RND(a1)
r2 := RND(a2)
r3 := RND(a3)

Requirements

Intrinsic	Architecture
_mm_round_ps	x86, x64

Header file <smmintrin.h>

Remarks

r0-r3, a0-a3, and b0-b3 are the sequentially ordered 32-bit components of return value r and parameters a and b, respectively. r0, a0, and b0 are the least significant 32 bits.

The rounding function uses the cntrl parameter to determine how to compute a new value. The following table indicates what rounding mode will be used.

Rounding mode	Value	Description
_MM_FROUND_TO_NEAREST_INT	0x0	Round to nearest (even).
_MM_FROUND_TO_NEG_INF	0x1	Round down (toward -∞).
_MM_FROUND_TO_POS_INF	0x2	Round up (toward +∞).
_MM_FROUND_TO_ZERO	0x3	Round toward zero (truncate).
_MM_FROUND_CUR_DIRECTION	0x4	Use current MXCSR setting.

This table shows how cntrl determines whether an exception should be signaled when a SNaN is detected.

Precision exception handling	Value	Description
_MM_FROUND_RAISE_EXC	0x0	Signal precision exception on SNaN.
_MM_FROUND_NO_EXC	0x8	Do not signal precision exception on SNaN.

The following macros are also available to combine the above two fields:

Rounding mode and precision exception handling	Value
_MM_FROUND_NINT	MM_FROUND_TO_NEAREST_INT | _MM_FROUND_RAISE_EXC
_MM_FROUND_FLOOR	_MM_FROUND_TO_NEG_INF | _MM_FROUND_RAISE_EXC
_MM_FROUND_CEIL	_MM_FROUND_TO_POS_INF | _MM_FROUND_RAISE_EXC
_MM_FROUND_TRUNC	_MM_FROUND_TO_ZERO | _MM_FROUND_RAISE_EXC
_MM_FROUND_RINT	_MM_FROUND_CUR_DIRECTION | _MM_FROUND_RAISE_EXC
_MM_FROUND_NEARBYINT	_MM_FROUND_CUR_DIRECTION | _MM_FROUND_NO_EXC

Before you use this intrinsic, software must ensure that the underlying processor supports the instruction.

Example

#include <stdio.h>
#include <smmintrin.h>

int main ()
{
    __m128 a;
    const int cntrl = _MM_FROUND_FLOOR;

    a.m128_f32[0] = 9.9375;
    a.m128_f32[1] = 5964.125;
    a.m128_f32[2] = -237.875;
    a.m128_f32[3] = -0.125;

    __m128 res = _mm_round_ps(a, cntrl);

    printf_s("Original a: %f\t%f\t%f\t%f\n",
                a.m128_f32[0], a.m128_f32[1], a.m128_f32[2], a.m128_f32[3]);
    printf_s("Result res: %f\t%f\t%f\t%f\n",
                res.m128_f32[0], res.m128_f32[1], res.m128_f32[2], res.m128_f32[3]);
    return 0;
}

Original a: 9.937500    5964.125000     -237.875000     -0.125000
Result res: 9.000000    5964.000000     -238.000000     -1.000000

See Also

Concepts

Compiler Intrinsics