Stefano Tommesani

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Home SIMD Detecting MMX and SSE

Detecting MMX and SSE


The MMX instructions are supported by every x86 processor introduced in the market after the venerable Intel Pentium MMX, so it should be fairly safe to assume that the processor that your code is running on has MMX instructions. But checking for MMX instructions is really simple and it avoids embarassing crashes due to unsupported opcodes!
The following C function checks for MMX:

bool isMMXSupported()
  int fSupported;
   mov eax,1 // CPUID level 1
   cpuid  // EDX = feature flag
   and edx,0x800000 // test bit 23 of feature flag
   mov fSupported,edx // != 0 if MMX is supported
  if (fSupported != 0)
   return true;
   return false;

I call ISSE the integer subset of the SSE instruction set that enhances MMX. Click here to see what processors support ISSE.
The following C function works on both Intel and AMD chips:

bool isISSESupported()
   int processor;
   int features;
   int ext_features = 0;
   __asm {
    mov eax,1
    mov processor,eax     // Store processor family/model/step
    mov features,edx      // Store features bits

    mov eax,080000000h
    // Check which extended functions can be called
    cmp eax,080000001h      // Extended Feature Bits
    jb  no_features         // jump if not supported

    mov eax,080000001h      // Select function 0x80000001
    mov ext_features,edx  // Store extended features bits

   if (((features >> 25) & 1) != 0)
    return true;
    if (((ext_features >> 22) & 1) != 0)
     return true;
     return false;


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