denormals.h

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// Denormals stripping.
// These snippets should be common enough to be considered public domain.
 
#ifndef LMMS_DENORMALS_H
#define LMMS_DENORMALS_H
 
#ifdef __SSE__
#include <immintrin.h>
#ifdef __GNUC__
#include <x86intrin.h>
#endif // __GNUC__
#endif // __SSE__
 
 
namespace lmms
{
 
#ifdef __SSE__
 
// Intel® 64 and IA-32 Architectures Software Developer’s Manual,
// Volume 1: Basic Architecture,
// 11.6.3 Checking for the DAZ Flag in the MXCSR Register
int inline can_we_daz()
{
  alignas(16) unsigned char buffer[512] = {0};
#if defined(LMMS_HOST_X86)
  _fxsave(buffer);
#elif defined(LMMS_HOST_X86_64)
  _fxsave64(buffer);
#endif // defined(LLMS_HOST_X86)
  // Bit 6 of the MXCSR_MASK, i.e. in the lowest byte,
  // tells if we can use the DAZ flag.
  return ((buffer[28] & (1 << 6)) != 0);
}
 
#endif // __SSE__
 
// Set denormal protection for this thread.
void inline disable_denormals()
{
#ifdef __SSE__
  /* Setting DAZ might freeze systems not supporting it */
  if (can_we_daz()) {
    _MM_SET_DENORMALS_ZERO_MODE( _MM_DENORMALS_ZERO_ON );
  }
  /* FTZ flag */
  _MM_SET_FLUSH_ZERO_MODE( _MM_FLUSH_ZERO_ON );
#endif // __SSE__
}
 
} // namespace lmms
 
#endif // LMMS_DENORMALS_H