int (*Foo_Ptr)(int);
PROCESSOR p;
ProcessorInfo(&p);
if(p->hasSSE2) Foo_Ptr=Foo_SSE2
else if(p->hasSSE) Foo_Ptr=Foo_SSE
else if(p->hasMMX) Foo_Ptr=Foo_MMX
else Foo_Ptr=Foo;

Example 2: Setting up vectors.