Recent searches
Search options
https://gcc.godbolt.org/z/YhrEcb7nz
Am I correct assuming that fmadd and vmul/vadd versions might not give me the exact same results (down in Test)? (Double checking.. )
gcc.godbolt.orgCompiler Explorer - C++ (x64 msvc v19.latest)using __vec4 = __m128;
__vec4 __vdot3ns(const __vec4& a, const __vec4& b)
{
__vec4 product = _mm_mul_ps(a, b);
__vec4 y = _mm_movehdup_ps(product);
__vec4 z = _mm_movehl_ps(product, product);
__vec4 sum = _mm_add_ss(product, y);
return(_mm_add_ss(sum, z));
}
float Pred(const __vec4& a, const __vec4& b)
{
__vec4 result = __vdot3ns(a, b);
return(reinterpret_cast<float*>(&result)[0]);
}
void Test(__vec4* _First, __vec4* _Last, const __vec4& x)
{
if (_First != _Last) {
for (auto _Mid = _First; ++_Mid != _Last;) { // order next element
auto _Hole = _Mid;
auto _Val = (*_Mid);
if (Pred(_Val, x)<Pred(*_First, x)) { // found new earliest element, move to front
//_Move_backward_unchecked(_First, _Mid, ++_Hole);
*_First = (_Val);
} else { // look for insertion point after first
for (auto _Prev = _Hole; Pred(_Val,x)<Pred(*--_Prev,x); _Hole = _Prev) {
*_Hole = (*_Prev); // move hole down
}
*_Hole = (_Val); // insert element in hole
}
}
}
}
... thanks for confirmations.. Practice agrees as well and sometimes the sort will explode :) (this was a copy-pasted bit of some of the <algorithm> sort code)
@msinilo is fp:fast generally worth the trouble it causes? It could lead to even simpler cases like compiler turning (a+b)+c into a+(b+c) which is not the same. And yeah, sorting predicates can and will go wrong with things like that.
