`_set_SSE2_enable`

Article
10/26/2022

Enables or disables the use of Streaming SIMD Extensions 2 (SSE2) instructions in CRT math routines. (This function isn't available on x64 architectures because SSE2 is enabled by default.)

Syntax

int _set_SSE2_enable(
   int flag
);

Parameters

flag
1 to enable the SSE2 implementation; 0 to disable the SSE2 implementation. By default, SSE2 implementation is enabled on processors that support it.

Return value

Nonzero if SSE2 implementation is enabled; zero if SSE2 implementation is disabled.

Remarks

The following functions have SSE2 implementations that can be enabled by using _set_SSE2_enable:

The SSE2 implementations of these functions might give slightly different answers than the default implementations. SSE2 intermediate values are 64-bit floating-point quantities, but the default implementation intermediate values are 80-bit floating-point quantities.

Note

If you use the /Oi (Generate Intrinsic Functions) compiler option to compile the project, it may appear that _set_SSE2_enable has no effect. The /Oi compiler option gives the compiler the authority to use intrinsics to replace CRT calls; this behavior overrides the effect of _set_SSE2_enable. If you want to guarantee that /Oi does not override _set_SSE2_enable, use /Oi- to compile your project. This might also be good practice when you use other compiler switches that imply /Oi.

The SSE2 implementation is only used if all exceptions are masked. Use _control87, _controlfp to mask exceptions.

Requirements

Routine	Required header
`_set_SSE2_enable`	<math.h>

For more compatibility information, see Compatibility.

Example

// crt_set_SSE2_enable.c
// processor: x86
#include <math.h>
#include <stdio.h>

int main()
{
   int i = _set_SSE2_enable(1);

   if (i)
      printf("SSE2 enabled.\n");
   else
      printf("SSE2 not enabled; processor does not support SSE2.\n");
}

SSE2 enabled.

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