Microsoft Specific
Emits the Streaming SIMD Extensions 4 (SSE4) instruction roundpd. This instruction rounds a 64-bit value by using the specified rounding control.
__m128d _mm_round_pd(
__m128d a,
const int cntrl
);
Parameters
[in] a
A 128-bit parameter that contains two 64-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)
Requirements
Intrinsic |
Architecture |
|---|---|
_mm_round_pd |
x86, x64 |
Header file <smmintrin.h>
Remarks
r0 and a0 are the low order 64 bits of return value r and parameter a. r1 and a1 are the high order 64 bits of return value r and parameter a.
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 Signaling Not a Number (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 ()
{
__m128d a;
const int cntrl = _MM_FROUND_NINT;
a.m128d_f64[0] = 127.5;
a.m128d_f64[1] = -315.125;
__m128d res = _mm_round_pd(a, cntrl);
printf_s("Original a: %f\t%f\n", a.m128d_f64[0], a.m128d_f64[1]);
printf_s("Result res: %f\t%f\n", res.m128d_f64[0], res.m128d_f64[1]);
return 0;
}
Original a: 127.500000 -315.125000 Result res: 128.000000 -315.000000