> Are there flaws in some ARM64 instructions? The result of (IEEE 754) operations -- including PLUS, MINUS and FMA -- is specified bit-for-bit, at least for `i

> Are there flaws in some ARM64 instructions? The result of (IEEE 754) operations -- including PLUS, MINUS and FMA -- is specified bit-for-bit, at least for `isnormal()` numbers. It is not a matter of vaguely "more precise" or "less precise". The test performed brings no information towards answering the question, because the loss of precision precision in one particular complex algorithm can perfectly well happen despite one individual operation having better worst-case precision. To check the unlikely event of a flaw in M1's FMA, one would need to compare the output of invidual FMAs with MPFR's output on the same operands. > ARM64 v Intel: I haven’t attempted to look at Intel processor fused instructions Instead, this test could have been a clue. FP64 results follow the spec and hence must be bit-for-bit equal across platforms (as long as one avoids legacy x87 on Intel).