Further request for clarification: float64(math.MaxFloat32) != float64(float32(math.MaxFloat32))

https://go.dev/play/p/feXsT2QSRIU

Why doesn't math.MaxFloat32 exactly represent the maximum finite value that can be stored in a float32? It may happen to produce the maximum-finite bit-pattern when stored in a float32, but is it still reasonable to claim that this is the maximum finite value that a float32 holds when it's not exactly that same finite value?

From strconv.FormatFloat:

The special precision -1 uses the smallest number of digits necessary such that ParseFloat will return f exactly.

So the "actual" you're generating here is not the actual value contained in the float. It is the shortest possible string that parses to that float.

fmt.Println I think also does not print with arbitrary precision. (It prints with "default format", whatever that means.)

If you print with %.0f it will give you the exact value. The resulting value is what is listed in comments for float32, and probably would be listed for float64 only it is too long.

	f32 := float32(math.MaxFloat32)
	fmt.Printf("f32:   %.0f\n", f32)
	fmt.Printf("f32    %x\n", math.Float32bits(f32))
	f64 := float64(math.MaxFloat64)
	fmt.Printf("f64:   %.0f\n", f64)
	fmt.Printf("f64    %x\n", math.Float64bits(f64))

Ah. I misunderstood. Thanks for the explanation!