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(* TEST
* native
*)
let ( *. ) x y = Sys.opaque_identity (x *. y)
(* Using opaque_identity should prevent use of FMA. *)
let f x = (x *. x -. x *. x)
(* The expression above can be compiled in two ways:
1. First evaluating x' = x *. x, then x' -. x'
The result is obviously zero.
2. First evaluating x' = x *. x, then x *. x -. x' as a single evaluation
step, using fused-multiply-add (or rather sub here).
FMA computes with increased precision because no rounding of the
intermediate computation happens.
In this case, the result is not always exactly 0.
See issue #10323. *)
let () =
assert (Int64.bits_of_float (f (sqrt 2.0)) = 0L)
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