Given a platform that supports the fused multiply add (FMA)
instruction and the code:
contract MA(t T) {
t * t + t
}
func ma(type T MA)(a, b, c T) T {
return a*b + c
}
Does the compiled-for-any-type version support the FMA optimization
when called with a floating-point type?
If not, does a specialized version, making the two different based on
whether the compiler chooses to specialize the function?
If I specifically want to not use the optimization when instantiated
with floats, can I do:
func maNoFMA(type T MA)(a, b, c T) T {
return T(a*b) + c
}
If I need it to use the guaranteed FMA intrinsic (see
https://github.com/golang/go/issues/25819 ) when instantiated with
floats, I can't do
func maMustFMA(type T MA)(a, b, c T) T {
switch a.(type) {
case float32:
return T(math.Fma(
float64(a.(float32)),
float64(b.(float32)),
float64(c.(float32)),
))
case float64:
return T(math.Fma(a.(float64), b.(float64), c.(float64)))
}
return a*b + c
}
because that misses cases like
type Float float64
so I have to use reflect which can't be dead-code eliminated during
specialization.
I'm sure there are other cases where similar questions could be asked,
but this seems like a good proxy for the whole class.
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